This paper proposes a decoupling technology of compact decoupling wall combining split resonant ring (SSR) and grid metal stubs for a two-element wideband and dual-polarized antenna array. By integrating the metal grid stubs and SSR on the same substrate to form a compact decoupling wall. The four identical compact decoupling walls are installed around the antenna array element to reduce the mutual coupling between the antenna array elements. The dimensions of the SRR and the grid metal stubs are optimized to achieve the best decoupling level for the array. The results demonstrate that the compact decoupling wall has the capacity to reduce the mutual coupling of the array from -13.8 dB to lower than -24 dB within 4.25 GHz - 4.98 GHz. In contrast, it almost does not affect the radiation characteristic of the array.

A systematic methodology is introduced for the design of broadband microstrip antennas (MAs) made of two stacked patches that are fed by an aperture coupled to an open-ended microstrip line. The MAs are modelled by an equivalent circuit (EC) consisting of two LC parallel resonators that are capacitively coupled, the EC being connected to the microstrip line by a LC series resonator that models the feeding. The circuit parameters are de-embedded from Momentum antenna simulations by using a novel technique based on the total least squares method. The EC of the MAs is adjusted as a second order filter with quasi-Chebyshev response, and the filter bandwidth is maximized so as to achieve broadband MAs. A MA has been designed with a center frequency of 5.57 GHz and a bandwidth larger than 30%. The MA has been fabricated and measured, and good agreement has been found between simulations and measurements.

We present the design of a wideband wide-scanning phased array for mobile communications. The array elements are connected slots in a dual-polarization configuration, radiating in the presence of a superstrate made of artificial dielectric layers (ADLs). Two interchangeable ADL superstrates have been designed, the former one allowing narrowband operation from 6 to 8 GHz (NB), and the latter one operating over a wide band between 2.3 and 8 GHz (WB). The performance is analyzed in terms of unit cell simulations, including the feeding structure. The NB design achieves an active reflection coefficient lower than -10 dB for scanning up to 60 degrees in all azimuthal planes. The WB design exhibits an active reflection coefficient lower than -6 dB for the same scan range. The designed feeding networks, based on microstrips and striplines for the two polarizations, respectively, are also presented.

This paper presents an ultra-wideband (UWB) compact size printed monopole antenna with improved gain and efficiency. This broadband printed monopole antenna contains a cup-shaped radiator fed by a coplanar waveguide (CPW) technique. The designed UWB antenna is fabricated on a less-priced FR-4 substrate with relative permittivity of 4.3, loss tangent of 0.025, and a standard height of 1.6 mm, sized at 31.68 mm × 23.76 mm × 1.6 mm suitable for wireless communication system. The designed UWB antenna works with maximum gain (peak gain of 5.5 dBi) across the whole UWB spectrum (3-11 GHz). The S11 results are simulated and measured and the results are debated in detail.

A methodology based on the design of antennas with the use of unit cells is presented in this paper. The methodology is applied to a previously presented 4-port cavity-backed MIMO antenna which is split in 4 identical unit cells due to its symmetric geometry. In the presented study, it is demonstrated that with the analysis of only the unit cell of the antenna the behaviour of the whole design can be predicted. Thanks to this methodology, the design of complex N-port antennas is simplified to the analysis of a unit cell and opens a new via for designing symmetric N-port antennas for massive MIMO applications.

A dual frequency (433 MHz and 2.45 GHz) circularly polarized MIMO rectenna with dual-branch rectifiers and a common power management unit is presented. For the lower frequency a dual-layer, four-element, monopole antenna array is implemented. The four monopoles are oriented along the perimeter of a square and are fed with 90° phase difference resulting in a circularly polarized antenna array. For the 2.45 GHz antenna, an elliptical patch is used implementing it in the middle of the square substrate that is used for the 433 MHz monopoles. The coaxial cables are connected on the dual-branch, dual-frequency rectifiers. The combined use of both frequencies results in RF-to-dc efficiency up to 70% for input power close to 0 dBm. The dual rectifiers have a common load since they are terminated with a common power management unit circuit.

The goal of this work is to study the performance of the Wireless Power Transfer (WPT) to inside the human body, while respecting the Specific Absorption Rate (SAR) limits. Therefore, the levels of absorbed power in different body parts were verified by simulation, in order to reach conclusions about the user's safety. More specifically, two biological models that represent the thigh and the arm were considered. The simulation results led us to conclude that it is possible to transmit approximately 140 mW on the limbs location, while respecting the SAR limits. In turn, it is possible to receive a power superior to 93 µW inside the human body. Additionally, real tests were also carried out in three subjects to verify the power attenuation related to each body structure.

In this work, the authors demonstrate the potential of 5G/mm-wave signals, coupled with wide-coverage Rotman-lens-based harvesters (a.k.a. tag) to achieve efficient and long-range powering. First, the rationale for the approach is described, before the elements of the harvester and their design specifications are presented and their performance is reported. Finally, the emitting system is detailed, followed by the presentation of its use with the tag to demonstrate long-range wireless power transfer (WPT) at mm-wave frequencies. For the first time, a relatively-compact rectenna system is shown to be able to collect 5G signals at ranges exceeding 16 m with a wide angular coverage, thereby extending the range relative to previous efforts by more than 5x and demonstrating a pathway towards the emergence of the Wireless Power Grid (WPG), a key to enabling the accelerated deployment of energy-autonomous wireless sensors ubiquitous constellations for digital twinning, smart cities, and intelligent infrastructure.

In this paper, a compact broadband CPW-fed circularly polarised elliptical-slot antenna with an inverted-L tuning stub is proposed. The antenna impedance is optimized for broadband operation from 1.62 GHz to 2.97 GHz. The measured CP bandwidth is 934 MHz (1.747-2.681 GHz), that covers common wireless communication bands GSM 1800, GSM 1900, 3G/LTE 2100, 3G/LTE 2300, 4G/LTE 2500, and 2.4G Wi-Fi bands. This makes the designed antenna an appropriate candidate for ambient RF energy harvesting purposes.

In this paper, we propose a novel radial line planar phased array in which helical antenna elements are individually rotated by their respective connected micromotors to realize dynamic beam-scanning. We designed, fabricated, and evaluated a 7-circle array with 168 helical antennas fabricated using molded interconnect device technology. The prototype antenna exhibits dynamic and accurate beam-forming performance, and also exhibits a low reflection coefficient of less than −17 and high antenna efficiency of 77%.

ERA5 reanalysis provides meteorological parameters that can help to predict atmospheric propagation effects. We investigate the accuracy of using ERA5 single level parameters, TCWV and TCLW, to calculate water vapor and cloud attenuation, respectively, in El Alto (4065 m.a.s.l, Bolivia) and Madrid (633 m.a.s.l, Spain), locations having different climatological conditions. The assessment is performed using as reference the attenuation predicted by physical models combined with atmospheric vertical profiles from radiosondes: 4 years (El Alto) and 8 years (Madrid). The most recent global prediction models from ITU-R are also implemented to complete testing analysis: P.676-12 and P.804-8 global maps based methods. The results obtained show that water vapour attenuation from TCWV predict statistics than can be used with small errors. Cloud attenuation from TCLW show large discrepancies in El Alto. However, in Madrid, good agreement with RAOBS-based statistics is observed when using Salonen08 Tunned model as cloud detection model.

The objectives and the preliminary results of the RadioSatMet numerical simulator are here described. The simulation chain is aimed at assessing the radio-propagation channel over the coverage region of a geostationary satellite communication (SatCom) system, featuring adaptive techniques as smart gateway diversity, through link quality estimates provided by its ground terminals as well as numerical weather prediction data. The RadioSatMet channel assessment system generates short-term statistical nowcasts and forecasts of the propagation conditions in each point of the coverage area. The RadioSatMet channel assessment output feeds an end-to-end system simulator, which evaluates the performances of the SatCom system with a particular focus on its gateway stations, in terms of data throughput, number of gateway switches and availability gains that can be achieved by using these methods.

The power spectra associated with wideband transionospheric signals received at Ascension Island (7.93oS, 14.25oW) during an observational campaign in October 2016 displayed flat and selective fading. The present contribution will combine the Method of Moment with the thin amplitude and phase screen formulation, in an attempt to identify structures that could be responsible for the observed behavior.

With increasing data rate requirements on SatCom systems there is a push to use higher frequency carriers. Although free space optical communications would meet these demands, they are severely limited by the weather conditions affecting the ground stations. Therefore, it is important to model these phenomena to predict the possibility of link outages so that an appropriate fade mitigation technique can be applied. This contribution aims to extend a model in the literature (Stochastic Model of Clouds) to include the time variability of the cloud field. The temporal evolution is studied using satellite observations and is introduced into the model by inputting ERA5 data chronologically, which has been linearly interpolated to a temporal resolution of 1 minute. The new model is then used to study the effect of site diversity for the mitigation of cloud attenuation on a GEO-Earth optical link operating at 1.55 μm.

The internal structure of small solar bodies are not well-known yet. The imaging of the interior of asteroids and comet will provide important information about their formation. In this paper, we aimed to provide a fast and efficient method to roughly image the shape and the interior of small bodies of the Solar system. We focused on monostatic measurements on two analogues of the 25143 Itokawa asteroid. The back-propagation technique was applied to promptly image the shape and internal structure of the analogues. The result shows the external shape of the analogue and that the inner void core can be reached and distinguished.

The topology optimization based on iterative changes of discretization is introduced. The optimal solution on coarse discretization is translated and enhanced on dense discretization. The similarity matrix used for solution translation is defined. Two examples of Q-factor minimization are shown to depict improvements in evaluation speed.

The problem of computing 2D EM wave scattering from rough surfaces is addressed using an integral equation formulation discretised using the method of moments. Successive Symmetric Over-Relaxation (SSOR) is applied to the governing matrix equations along with eigenvalue deflation which is designed to separately account for the effect of those eigenvectors of the iteration matrix that have eigenvalues greater than 1. Numerical results are presented applying the method to a variety of scattering profiles and examining the resultant convergence performance.

We present a boundary element method for electromagnetic scattering analysis, formulated in terms of the magnetic vector and electric scalar potentials rather than electromagnetic fields. The proposed potential-based formulation does not rely on the mutual coupling between electric and magnetic fields, and is therefore able to simulate dielectric objects over a wider range of frequency than is possible with state-of-the-art field-based methods, as demonstrated via numerical examples.

For waveguide devices, Mode-Matching represents one of the most widely used tools to compute the electromagnetic behaviour of structures due to its ability for the accurate modelling of discrete discontinuities. As devices with higher-order symmetries appear in the literature, it becomes relevant to study how it would affect the technique to use sets of modes which also have higher-order symmetry properties, such as discrete rotational symmetry. In this paper we provide a tailored Mode-Matching formulation which is capable of handling rotationally symmetric modes, while also discussing its most important properties. It has been used to analyse a variety of devices appearing in existing literature, in all of them greatly reducing the computational time and amount of modes needed for their correct modelling with regards to general-purpose Mode-Matching.

The physical optics (PO) approximation is widely used for scattering analysis involving electrically very large objects. A key step in its application is structural shadowing determination with respect to the source field. This requires determining which parts of the scatterer are visible (line-of-sight) to the source. The results presented in this paper are concerned with plane wave illumination shadowing determination for mesh-based PO. The authors have been developing a multi-level field-of-view buffer-based shadowing determination algorithm with the objective of yielding linear (optimal) runtime scaling even under very extreme circumstances. This paper reports the most recent results obtained with this algorithm, comparing it with a multi-level quadtree-based reference scheme, for a challenging example featuring both severe mesh inhomogeneity and grazing incidence. Linear runtime scaling is demonstrated. Further results will be presented at the symposium.

This paper reports the conceptualization, and analysis of a geometrical approach to determine the shift in the in-phase reflection of three conformal meta-surfaces (MS). For the proposed approach, a planar array consisting of MS unit cells (MS-UCs) of a given dimension is drawn on a circle of desired radius (r). The path traveled by the reflected and incident EM wave in terms of an electrical length results in the shift of reflection angle. For the validation purpose, the conformed arrays are simulated under x- and y-polarized EM waves. The sum of the incident and reflected phases resulting in total shift is determined theoretically and compared with the simulated shifts of the three arrays. Furthermore, one of the conformed arrays is experimentally evaluated under the TEM incidence and compared with the theoretical and simulated result. The excellent agreement between the theoretical and measured results demonstrates the effectiveness of the proposed work.

In this paper, the scattering of a Bessel beam by PEC and dielectric circular cylindrical scatterers is analyzed and discussed. In particular, it is shown that the scattering by nondiffractive beams is in general spatially localized in both cases, due to the remarkable focused beam features: the wavefront inside the main beam is locally planar, and the sidelobes are not so high, due to the abrupt amplitude shaping of the zeroth order Bessel distribution. The inherent localized scattering process paves the way to novel applications in microwave imaging and ground penetrating radar design.

In this paper, a substrate integrated waveguide (SIW) loaded with three pairs of modified complementary split-ring resonators (CSRRs) is presented, in which the subwavelength waveguide passband can be significantly increased due to the appearance of new electromagnetic couplings between the different resonators. The obtained results are compared to those provided by a more classical topology based on CSRRs periodically etched along the waveguide wall, showing a significant bandwidth improvement, while maintaining a good matching level.

A novel design of a dual band metasurface unit element using two diodes for independent phase shifting in two frequency bands with low reflection losses is presented. Control of the capacitance and thus of the reflected phase can be achieved by independently applying a reverse bias to the two air-bridged Schottky diodes that are embedded on the phase-shifting element. Simulations of the proposed design are presented and the currents and losses are studied. CST Microwave Studio was used to evaluate the tuning range and reflection characteristics of the proposed design.

This paper presents a 2-bit unit cell for reconfigurable intelligent surface (RIS) applications of beamforming and beam-steering in the frequency range 2 (FR2) from the fifth generation of mobile communications (5G). The proposed unit cell is based on a printed split-ring resonator (SRR) loaded with a varactor diode. The SRR-based structure comprises two circular loops connected by a varactor diode at the top and a ground plane at the bottom, resulting in a 0.245x0.245λ0 total area. The complete unit cell element encompasses four conducting layers, in which the first two ones form the SRR. RF chokes are printed at the middle layer to isolate the DC circuit, and the bias lines are routed at the fourth layer. The unit cell has been conceived using the full-wave electromagnetic solver ANSYS HFSS. Its numerical results demonstrate a reflection phase shift up to 270º and reflection magnitude higher than 0.5 at 24.5 GHz.

This paper presents a detailed investigation of the propagation of noise generated by a switch mode power supply (SMPS) across an automotive sensor Printed Circuit Board (PCB). The noise propagation is simulated using a full 3D model of the board. CST Studio Suite was used to import the PCB and component models, perform the simulations and visualize the surface current distribution and the corresponding noise distribution. The paper demonstrates how the ground vias arrangement is critical for full understanding of propagation of the noise and its mitigation.

We propose an alternative metasurface-based approach for the synthesis of Bessel beam launchers at microwaves/millimeter waves, based on an inward cylindrical traveling wave aperture distribution. Our approach simply allows the outward-to-inward cylindrical feeding wave conversion by metallic dihedrons. Although more involved from the manufacturing viewpoint with respect to single layer devices, it can in principle avoid the computationally-heavy design of holographybased Bessel beam launchers. The preliminary numerical results show the effectiveness of the proposed technique.

Additive manufacturing offers new possibilities in the design of innovative antennas. In order to fully exploit its potential, it is necessary to fully use the capabilities offered by the 3D printing technology. 3D-printed structured dielectrics are currently receiving a lot of interest in this respect. However, the characterization of the dielectric properties of such crystal structures is not easy and often assumptions on such properties need to be done. This paper shows a characterization of additively manufactured structured dielectrics in terms of their permittivity and loss tangent in a simple cubic (SC) and face centered cubic (FCC) crystal geometry with different fill fractions. Measurement results are compared to values predicted by the Maxwell-Garnett effective media approximation or by the effective refractive index extracted from a three-dimensional plane wave expansion method (PWEM) in the long wavelength limit.

A single-layer frequency selective surface (FSS) polarizer is proposed as a linear-to-circular polarization converter, operating at 5.2 GHz for 5G applications. The analyses are based on the magnitude and phase of the transmission coefficient of two orthogonal electric field components. The four-arms star geometry used in the FSS polarizer is simple to design, and equations are provided. The design approach is validated by a good agreement between numerical and measured results.

The problem of electromagnetic plane wave scattering by doubly periodic dielectric structures composed of spherical radially inhomogeneous absorbing elements of black hole type arranged on a perfectly conducting screen is considered. An algorithm accounting for the features of the black holes is developed on the basis of the hybrid projection method for solution of the problem. A number of numerical results characterizing both the effectiveness of the algorithms themselves and the properties of the black-hole-based absorbing structures are presented and discussed.

This paper presents the design of an AFSR backed low RCS dipole antenna. The polarization-insensitive AFSR structure consists of a reflection notch within the two broad absorption bands. A dipole antenna having operating frequency synchronized with the reflection notch of the AFSR structure is integrated with the 6 x 6 array of the AFSR unit cell. The AFSR backed dipole exhibits an RCS reduction of more than 20 dB at the side-bands of the operating frequency for TE and TM polarized incident waves without any significant degradation in the antenna performance. The AFSR integrated dipole shown an enhancement in the gain by 1.27 dB in the broadside direction. The proposed AFSR being polarization-insensitive, can suitably be employed for the RCS reduction of a dual-polarized/circularly polarized antenna in future works.

This paper presents a 3-D printing-compatible wideband absorber with high angular robustness. A periodic structure, composed of Hanoi-Tower shaped resonators, is fabricated with a lossy 3-D printable dielectric material using additive manufacturing, and glued on a magnetic elastomeric material. Exploiting the resonating modes in the periodic resonators, high absorption is achieved over a large bandwidth. The resonators' shape and dimensions are chosen accordingly to the material properties so that a high angular robustness is reached. Moreover, the presence of a magnetic support enhances the absorption capabilities of the structure, specially for the TM polarization, where a reflectivity below -10 dB for most incident angles over the 4-12 GHz band is reached. Finally, diffraction phenomena happening at high frequencies are studied, showcasing that high-order diffraction can be avoided by reducing the size of the structure and increasing the permittivity of the dielectric material.

In this study, we propose a multi-functional unit-cell that integrates reflectarray and linear polarizer functions together. The unit-cell is composed of a multi-layer structure and depending on the polarization, it can perform as a reflectarray or transmission type linear polarization converter. Our results demonstrate that in the reflection mode, the unit-cell shows high reflection magnitude around one and a nearly full phase coverage of 310° at 14GHZ. In the transmission mode, the unit-cell functions as a highly efficient linear polarization converter with PCR more than 95% in the broad frequency range of 3 GHz to 14 GHz. Our results reveal that the proposed unit-cell is suitable for multi-functional applications such as bidirectional wireless Communication.

A MLFMM-FFT based strategy for the computation of electromagnetic (EM) radiation and scattering in dielectrics is presented. The objective is to reduce the computational resources required for the application of the method of moments (MoM) to problems with electrically large dielectric structures. For this purpose, the storage of the near-field couplings in the MLFMM algorithm is reduced taking advantage of the Toeplitz symmetries present in regular hexahedral meshes. Therefore, the rigorous MoM matrix becomes smaller, thus significantly reducing the amount of memory required for the computation in this kind of problems. The FFT is employed for a fast computation in the convolutions required in the near-field part of the algorithm. In addition, a new approach for the numerical treatment of the transitions between dielectrics and dielectric and the free space is introduced.

A volumetric method of moments (V-MoM) for the analysis of integrated antennas is presented here. The developed numerical procedure discretizes the domain with a uniform and hexahedral mesh. For antennas radiating in the presence of dielectric slabs or lenses, the discretization required for the dielectric materials is typically coarser than the one required for the antenna. To enable a uniform mesh, a technique is proposed that allows efficient simulations of the dielectric together with the antenna feed. The antenna is first analyzed in a homogenous infinite medium. Subsequently, an auxiliary antenna is defined that is equivalent in terms of impedance, but characterized by much coarser details. The auxiliary antenna is then analyzed together with the finite size dielectrics, with a computationally efficient simulation.

The paper reports a second-order approximation of the transition boundary condition for not very thin layers of non-dense materials. It allows reconstructing with an error of less than 1% the scattering from a dielectric slab characterized by a thickness of the order of a tenth of wavelength, even when the relative dielectric constant is 2. Furthermore, the independence of the formulation from the incidence angle of the impinging wave allows its implementation in a numerical method as the method of moments.

Fundamental bounds play an important role in antenna design. Using method of moments and electric field integral equation, this paper shows a formulation of fundamental bounds based on quadratically constrained quadratic programs. This methodology is applied to two representative and challenging examples. The first example examines Yagi-Uda antenna and compares it with performance limits on Q-factor, radiation efficiency, and directivity. The second example shows how to determine fundamental bounds when a designer has far-field constraints. In their entirety, the examples demonstrate variability and generality of this treatment and also recall the existence of an open-source computational package, which can be used for evaluation of fundamental bounds on various metrics including their mutual trade-offs.

This article presents a simple matching technique to control surface-waves (SWs) by using a finite metasurface matching section. The approach is based on a sub-wavelength array of patches which are employed as a simple and effective approach to control and guide SWs on a grounded dielectric slab (GDS). In order to excite the fundamental TM0 SW mode, a horn-shape surface-wave launcher (SWL) in substrate integrated waveguide (SIW) technology is employed. The structure and the matching metasurface are modeled with an equivalent circuit.

This paper presents a novel technique to implement crossed dipole antenna fed by Substrate Integrated Coaxial Line (SICL) technology. The inherent advantage of out of phase surface current of the SICL transmission line is utilized efficiently to excite the two dipole antennas. The crossed dipole is implemented to obtain dual band response at 26 GHz and 28 GHz. Two 45 inclined dipoles are printed on the top/bottom of the substrate and simultaneously fed by top/bottom plate of the SICL line. SICL 1:4 power divider is employed to feed four crossed dipole antenna to form an array. The array exhibits a gain of 9.7 dBi and 10 dBi at 26 GHz and 28 GHz respectively exhibiting wide 3.1 GHz bandwidth . The cross polarization better than 20 dB is obtained for the proposed design. The proposed antenna finds its suitability for the much focused 5G millimeter wave frequency bands.

The design and numerical simulations of a microwave sensor for the moisture content of traditional Carasau bread is presented in this paper. The results highlight the ability of a simple patch antenna to discriminate small percentage variations in water content in the food product, avoiding misinterpretations due to other parameters modifications, such as distance of the sensor and thickness of the bread sample.

The Industry 4.0 paradigm calls for engineering solutions for monitoring the industrial production and quality of food products. Microwave devices can be powerful tools in this scenario. This work deals with the preliminary design of a double ridge waveguide to perform indirect measurements of the complex permittivity of a traditional food product from Sardinia (Italy), i.e. the Carasau bread, produced in a small bakery industry. To this aim, the complex dielectric permittivity of doughs was measured with open-ended coaxial probe in the range 0.5-8.5 GHz. The dielectric spectra were fitted to a third-order Cole-Cole model. Then the data were used to numerically study the microwave signal propagation in the double ridge waveguide investigating different sample configurations. With our full-wave simulations, the thickness of the sample holder, the occupation length of the sample in the waveguide, as well as the inclination angle were determined to achieve suitable transmission performance.

In this paper, a Chipless RFID tag design based on Radar Cross Section (RCS) operating principle is proposed. The tag is implemented using a series of circular ring resonators to enable tag identification. The resonators are simulated and then fabricated on an FR4 substrate. A calibration technique using a ring resonator to improve the detection of 8-bit data is proposed and demonstrated. The fabricated tag is measured at a distance of 160 mm using the monostatic RCS method. The measurement results verify the simulation results and show accurate detection of the encoded information.

The technological advances in electronic devices and the Internet of Things bring us to be surrounded by multiple sensors in the coming years. These devices should be conformable and adapted to small or irregular shapes and surfaces. This is why flexible materials are becoming important in this field thanks to their lightness, stretchability, and robustness especially in wearable electronics to get integrated on clothes for biomonitoring. Our proposal in this paper concerns the design, printing process, and performance of a novel antenna on a polyimide flexible substrate. It is based on a loop antenna and has dimensions of 40 mm × 35 mm × 0.127 mm. Its very wideband behavior from 2.4 GHz to 4 GHz allows targeting S-Band applications such as LTE and Wi-Fi. Interesting performances are also achieved in terms of radiation patterns. At 2.45 GHz, the maximum antenna gain is about +2.6 dBi with an omnidirectional pattern but at higher frequencies, the antenna is more directive with a higher gain.

A compact and broadband coplanar waveguide (CPW) fed ring pair slot antenna is presented in this paper. The designed antenna operates in the frequency range from 2.6 to 7.13 GHz (93%) for |S11| ≤ -10 dB with a peak gain of 5.06 dBi at 5.6 GHz. The designed antenna is uniplanar having the size of 0.39λ0 × 0.3 λ0 ×0.007 λ0 (λ0 is the wavelength at the lowest operating frequency in free space). The proposed configuration has a stable radiation pattern over the operating frequency band. The designed antenna is fabricated and simulated results are validated with measured results.

The procedure of estimating the angular dependent delay of an Ultra Wideband (UWB) antenna, directly in frequency domain, is presented. It is shown that in this approach any occurrences that can lead to inaccurate results, such as the windowing effect, can be entirely avoided. It alleviates the need to design a specific pulse, since the transfer function can be obtained by a frequency sweep. Moreover, polarization mismatch is accounted in the analysis. To this end, an UWB monopole antenna is designed and it is simulated with time and frequency domain solvers. The simulation results demonstrate that only frequency domain analysis is sufficient for the delay estimation. The outcome of this work provides a clear procedure for obtaining the angular dependent delay of an antenna in an accurate way.

This paper presents an Ultra-Wideband (UWB) patch antenna which is aimed to be an Anchor-antenna in UWB localization systems. It can operate distinctively in two different UWB frequency channels. Both of these channels have 500 MHz bandwidth, the lowband channel is centered at 4 GHz and the highband channel at 6.49 GHz. Reconfigurability to switch from one channel to another is achieved by changing the size of the radiating element. Additionally, this UWB antenna is aimed to be circularly polarized over both channels, which is realized through two branchline couplers placed on a bottom layer. Results of reconfigurability and circular polarization operation are verified by simulation and measurements.

A compact low-loss reconfigurable phase shifter based on gap waveguide (GW) is proposed. The phase shifter is realized by controlling the different lengths of the transmission line. A movable metal block is placed on the transmission line, and different phase shifts can be obtained through different moving distances to realize reconfiguration. In this paper, the possible errors in practical application are considered and the solutions are given. The use of GW technology enables the design to achieve low-cost manufacturing and simple implementation. The simulation S-parameters show that the impedance matching bandwidth with reflection coefficients below −15 dB is 19.1%, covering 71 − 86 GHz, and the maximum phase shift of 180° can be achieved.

A feasibility study to design a complex X/Ka-band feed system that also incorporates a Ka-band Radar function is undertaken. An unconventional wide-band Ka-band polarizer design was needed due to the high-power nature of the application.

Reflector antennas systems use struts in order to antenna structural parts such as feeders or sub-reflectors. Struts' presence generates scattered fields that affect the antenna performance. In this paper, a comparative study between different struts' materials and cross-sections is presented. For the analysis, a Cassegrain configuration was used, designed for X-band operation. Struts' analysis was conducted through simulations at 8.425 GHz. Two different struts' positions (setups) were also studied. Detailed discussion on performance results is presented.

To reduce the coverage holes from the base station, reflectarray has gained attention for 5G mobile wireless communication. This paper proposes the design method for dual frequency and dual polarization reflectarray operating at 28 and 39 GHz. The proposed method combines the modified phase and pattern mask, which can reduce the sidelobe level of the dual frequency and dual polarization reflectarray. This paper demonstrates the reflectarray designed by the proposed method in simulation and measurement.

Broadband Pancharatnam-Berry (P-B) phase and dynamic phase hybrid unit cells for realizing dual circularly polarized (DCP) independent beam control reflectarrays is proposed. The unit cells present independent reflection phase shift for left hand circularly polarized (LHCP) and right hand circularly polarized (RHCP) incident waves, which are achieved by simultaneously utilizing P-B phase and dimension vary dynamic phase. A broadband P-B phase unit cell with reflection coefficient greater than -0.5 dB in the range of of 6.9-15.7 GHz (bandwidth of 77%) is designed, and then independent dynamic phase achieved by adjusting the dimension of the unit cell. Simulation results reveal the P-B phase shift range and dynamic linear phase shift range of the single-layer unit cells are 360◦ in the range of 8-12 GHz (bandwidth of 40%).

Estimation the reflected field phase, admittance and unknown basis functions coefficients are presented for the case of single-layer rectangular slot element in unit cell. The analysis is based on a solution of an integral-equation system with the Method of Moments in spectral domain. Only one basis function is used for the analysis. It is shown that this approach provides satisfactory accuracy for the development of the slot reflectarray antennas. Characteristics of the unit cell and reflectarray antennas obtained by proposed approach and full-wave simulations are presented.

An integrated lens antenna (ILA) is desired to have high directivity and a wide steering range. The directivity of an ILA is proportional to its diameter. In this work, the relation between the diameter and the scan loss of the elliptical and hemispherical ILAs is studied using the ray-tracing simulation. The simulation study finds that the scan loss of an ILA, both elliptical and hemispherical, is proportional to the diameter. In addition, the optimum extension lengths of the extended hemispherical ILA are presented for various diameters and relative permittivities which serve as the design guideline for ILA designers.

A gradient index flat lens with a directive beam-steering radiation pattern and configurable dual circular polarization is discussed in this contribution. The dielectric lens, designed to operate at W band, is perforated to achieve a radial decreasing dielectric permittivity characteristic, so high-directivity beam with planar wave front can be obtained. A precisely designed stereolithography 3D structure is adhered to the surface of the lens to turn the vertical or horizontal electric field polarization into RHCP (Right-hand circular polarization) or LHCP (Left-hand circular polarization), respectively. An open-ended square waveguide is used as feeding structure to generate the vertical and horizontal polarization exciting the two degenerate modes TE10 and TE01. The system can achieve a wide beam-steering range of ±30° in both azimuth and elevation planes, attained by applying precise displacements to the feeding square waveguide position. In order to experimentally validate the antenna performance, the design is manufactured and measured

In this study, a simple decoupling method using parasitic elements (PEs) connected by a bridge line (BL) for multiple planar inverted-F antennas (PIFAs) is proposed. The PEs and BL only need to be loaded in close proximity onto the PIFAs. Thus, redesigning the original antenna elements is not necessary. This feature is useful when design conditions make it difficult to redesign the original antenna, for example, to redesign small modular antennas. For the case of two PIFAs, using PEs and BL reduces the mutual coupling from −6.6 to −16.7 dB, and simultaneously maintains the resonance at the desired frequency (2.0 GHz), resulting in an improved total antenna efficiency from 77.4% to 96.0%. In the case of four PIFAs, the proposed method still showed its efficiency in decoupling, but some deteriorated efficiencies are also observed compared with the case of two PIFAs. This deterioration will improve in the future.

In this paper we present a technique to broaden the beamwidth of conventional patch microstrip antennas by using parasitic elements. This technique allows to keep the main advantages of microstrip antennas while increasing their beamwidth. We provide guidelines on how to tune the shape of the pattern from directive patterns to broad beam by tuning a few key parameters. The antenna that we propose operates in the ISM band at 2.4GHz and is compatible with linear and circular polarization. Using this technique, the beamwidth of a regular patch antenna can be increased from the usual 70º up to 200º, and is compatible both with linear and circular polarization.

In this article, three dual circularly-polarized K-band horn antennas are designed and experimentally validated. All designs are based on a common topology: a square waveguide input, a bowtie-shaped polarizer, and a flare section. Either left or right-handed radiation can be achieved by exciting either mode in the square waveguide. The bowtie polarizer outstands as a simple, easy-to-manufacture way of obtaining circular polarization. The three designs differ just in the flare section: a circular aperture, a square aperture and a bowtie-shaped aperture have been considered. The advantages of each aperture type will be discussed. The prototypes have been manufactured by Direct Metal Laser Sintering, allowing a single-block assembly. Over 20% bandwidth with axial ratio under 3 dB and gain around 19 dBi has been experimentally obtained.

This document follows a previous article \cite{eucap2021} which present the design of a Dielectric Resonator Antenna (DRA) developed by ANYWAVES with the support of the French Space Agency (CNES) and the help of an academic partner XLIM. This antenna is circularly-polarized, dual-band (Upper-L-Band (1.559 - 1.61 GHz) and TT\&C S-Band (2.025 - 2.29 GHz)) and designed to be integrated on a CubeSat or Nanosatellite. The particularity of this DRA is that the dielectric part is a structured 3D-printed block of Zirconia with two different permittivities. Two different feeding lines have been designed: with and without an integrated diplexer. Two breadboards of this antenna had been fabricated and measured in the premises of XLIM.

Parallel electromagnetic solvers require efficient strategies to distribute the mesh of large structures encountered in advanced antenna designs. In addition, parallel solvers based on the adaptive integral method (AIM) require processes to access additional mesh entities that lie within the near region of their mesh partition. In this paper, we propose a parallel solution for loading, processing, partitioning, and redistributing the mesh of AIM-based solvers. The proposed method is demonstrated on problems as large as 200 wavelengths, with up to 200 million unknowns, and up to 8000 cores involved.

This article presents a study of the tunable impedance matching to our recently reported compact self-matched triple-band brain-implantable planar-inverted-F antenna (PIFA). It operates at Medical Device Radiocommunication Service (MedRadio) band (401-406 MHz) and Industrial, Scientific, and Medical (ISM) bands (902-928 MHz and 2400-2483.5 MHz). To achieve this, we investigated the optimal reflection coefficient characteristics of PIFA at desired frequencies by employing four π- and T-type matching circuits. Our results show that a T-type circuit selected for further assessment provides suitable fine-tuning possibilities for all combinations of desired upwards and downwards frequency-tuning of the three operating frequencies to ensure reliable wireless implant communications.

With the exponential advancements realized in communication technologies, synthetic biology, and nanotechnology, now it is time to aim high and design new generation implants. To achieve this vision, this paper presents a novel sensing platform based on genetically engineered bacteria and a repeater antenna system, including a biodegradable in-body reflector antenna and on-body reader antenna. The biodegradation process is controlled by the engineered bacteria which in the future will be utilized to sense a molecule of interest. The biodegradation, hence, the sensing can be wirelessly tracked. In this paper, we present the control of biodegradation experimentally by the engineered bacteria and show the wireless tracking numerically. The sensing at 1 cm implant depth in fat tissue in the 2.4 GHz ISM band is demonstrated.

Two different bidirectional periodic leaky-wave antennas (LWAs) are presented for the millimeter-wave (mm-wave) band with suppressed stopbands and orthogonal radiation directions: a bidirectional side-fire antenna with left/right in-plane radiation and a bidirectional slot-pair antenna with top/bottom out-of-plane radiation. The operations of these antennas are confirmed using full-wave simulations, with a broadside frequency of approximately 28 GHz. These antennas can be individually engineered to form various radiation patterns in each of their radiation planes, and can further be combined to design a tetra-directional periodic LWA.

Compared to conventional uniformly spaced arrays, sparse arrays are effective and economical for many application scenarios. For example, sparse arrays can help to save on the number of antennas, and the supporting hardware costs, as well as improve the angular resolution which is useful for automotive radar systems and target identification applications. This paper will focus on implementing a hybrid approach to numerically determine an optimal 4x4 multiple-input multiple-output (MIMO) array considering simulated annealing and particle swarm optimization (SA-PSO). Results will show that the technique can achieve lower peak sidelobe level (PSLL) or narrower main lobe half-power 3dB beamwidth (3dB BW) with 8 fewer elements when compared to a corresponding 16 element uniform linear array (ULA). To the best knowledge of the authors, this is the first time that such a design technique has been applied to MIMO arrays whilst considering a hybrid SA-PSO synthesis algorithm.

With the application requirements of wireless technology in implantable bioelectronics, knowledge of the fundamental limits for implanted antennas becomes critical. In this work, we investigated the variation of maximum power density within simplified body phantoms, caused by changes in the operating frequency, implantation depth, body phantom radius, and source size. Both spherical and planar body models are studied, and the corresponding results are compared to an efficient approximation method. The summarized results are used to derive design rules and can be used as benchmarks for the design of most implanted antennas, especially for shallow implants.

A transparent spherical spiral antenna for endoscopy capsule systems for gastrointestinal monitoring is presented in this article. The capsule antenna is designed for operating in the Medical Implant Communication Systems frequency band (i.e., 401-406 MHz) and has an impedance bandwidth of 397-409 MHz. The transparency of the antenna allows it to be implemented in front of the camera. This leads to more available space inside the capsule for embedding more subsystems. The proposed antenna also has a circularly polarized omnidirectional radiation pattern. These characteristics allow a stable wireless communication link during the monitoring operation.

A circularly polarized implantable antenna working at 915 MHz industrial, scientific, and medical (ISM) band is presented. A meander line is used for miniaturization purposes, while a U-shaped structure is used not only to guarantee circular polarization performance but also to shift the band to lower frequencies. The designed antenna shows an impedance bandwidth of 20 % from 809.4 to 989.8 MHz and an axial ratio (AR) bandwidth of 27 % from 770 to 1010 MHz. The proposed antenna has a compact size of 5.2 mm × 5.6 mm. The proposed antenna achieves an acceptable gain value of -23 dBi. Furthermore, the geometry of the proposed antenna remains simple with a full ground plane and without using any via holes. Finally, the fabricated prototype has been experimentally tested inside minced pork, salmon fish, and beef meat, and the measured results show good agreement with the simulated one.

This work focuses on the investigation of the degree of possible detuning that may be observed in the impedance response of ingestible antennas during the transition through the gastrointestinal tract. For this investigation, two antennas are used: a meandered dipole and loop antenna. The antennas conform to the inner surface of the biocompatible capsule shell. They are optimized in spherical homogeneous time-averaged gastrointestinal phantoms at 3 frequencies of interest: 434 MHz, 1.4 GHz, and 2.4 GHz. Next, the optimized antennas are simulated in 3 different phantoms, each mimicking electromagnetic properties of one of the tissues in the gastrointestinal tract. The impedance response of each design in 4 different tissues is discussed. The results show that the maximum shift in the operating frequency is 7 MHz, indicating that the presence of the encapsulation layer makes the considered antennas robust against the changes in the electromagnetic properties encountered through the gastrointestinal tract.

This paper presents a possible solution to enhance electromagnetic transmission to an implantable/wearable device in wireless power transfer systems. Based on an analytical approach we have developed, we show how it is possible, using wearable dielectric cylindrical scatterers, to increase the intensity of the transmitted field to a possible receiver, which may be arranged in the textile fabric of a garment or implanted in the underlying biological tissue. In particular, we show some parametric studies on the dielectric constant of scatterers, which can be easily integrated into a fabric, showing which configuration achieves the greatest increase in electromagnetic transmission. The electrical parameters of the biological and textile tissues are considered in the millimeter frequency range (f = 24 GHz).

In this paper, a novel textile star-shaped supershaped patch antenna is proposed for 5G applications, operating at 3.5 GHz. The Gielis Formula, also called Superformula, was used to design the antenna and thus minimize its patch size. The characteristics of the antenna, such as return loss, realized gain and radiation pattern are simulated, and the return loss is compared with the measured results. The designed antenna attains a -45.48 dB return loss at 3.5 GHz, with operational bandwidth from 3.43 GHz to 3.56 GHz for -10 dB, with the peak gain around 8.5 dBi for 3.5 GHz.

A low-cost single-layer substrate-integrated waveguide (SIW) cavity-backed slot antenna is proposed for millimeter-wave applications. The structure is designed to operate at the W-band. The T-shaped slot antenna is placed on the back-side of the SIW and fed by a grounded coplanar waveguide (GCPW) transmission line. A transition between the (GCPW) and the SIW is also designed. The simulated results provide that the antenna has a stable gain over the frequency range (98.79-100.56) GHz with a maximum value of around 6 dBi also high radiation efficiency.

In this paper, a compact wideband antenna-inpackage (AiP) for 5G mmWave applications in the 39 GHz frequency band is presented. The proposed 1x2 antenna array consists of two identical patch antenna elements, which are designed, simulated and fabricated using a multilayer PCB substrate technology suitable for chip embedding. To improve the antenna bandwidth two U-shaped slots are etched in each patch element. The fabricated 1x2 U-slot patch antenna array exhibits a measured impedance bandwidth of 3 GHz at 39 GHz frequency band, and a measured peak gain of 8.8 dBi.

This paper presents an innovative and advanced miniaturized 5G module of wideband dual-polarized (pol.) millimeter-Wave (mm-Wave) antennas-in-package as non-mm-Wave antennas (AiPaA) for handsets. That is, the module of mm-Wave antennas-in-package (AiP) can also function as virtual equivalent non-mm-Wave antennas. This AiPaA module can cover 3GPP mm-Wave bands n257, n261, n260 and the mm-Wave band (24.75-27.50 GHz) in China. Moreover, without physical non-mm-Wave antennas, the module itself can operate in 3GPP non-mm-Wave bands n78 and n79. Thus, this AiPaA module can serve as a miniaturized compelling 5G antenna total solution to handsets without expanded volumes for physical non-mm-Wave antennas.

An innovative and practical integration of 5G millimeter-Wave (mm-Wave) antennas and 5G non-mm-Wave antennas based on the flexible printed circuit (FPC) for mobile phones is proposed. Therefore, the integrated antennas are well conformal to the curved phones shapes due to the flexible substrate. The integrated 5G mm-Wave antennas are in a 1 × 4 array which covers the 3GPP band n261 (27.5-28.35 GHz) and the two 5G non-mm-Wave antennas are integrated in an equivalent form by reusing the ground of the mentioned 5G mm-Wave antenna array to achieve MIMO function in the 3GPP band n79 (4.4-5.0 GHz). The FPC-based integrated 5G antennas (with a total length of 26.07 mm) can be attached on the inside of the curved edges of back covers to attain the elegant applications to mobile phones.

In this paper, we present an innovative sensor for non-invasive detection of millimeter inclusions by using a microwave radiating system. The proposed device consists in a microstrip self-resonant spiral coil inductively coupled to an external concentric planar probe loop, working at a frequency of 570 MHz. The microwave sensor configuration is the result of an optimization process of the spiral coil Q-factor maximization, required to obtain a millimeter resolution for the inclusions detection. In particular, the detection is achieved by observing the amplitude and frequency shift variation of the external planar probe input impedance. We performed full-wave simulations to design and evaluate the radiating system performance. Numerical results validated the introduced theorical approach, encouraging further analysis for the potential use of such sensor in biomedical applications.

One of the most common symptoms of respiratory pandemics, like COVID-19, is cough. Its monitoring is useful to trace the progress of the disease and to evaluate its severity. Traditional measurement methods are bulky and wired. Instead, wearable and wireless technologies such as the Radio Frequency Identification (RFID) could allow the implementation of platforms able to monitor patients remotely. The monitoring of the respiratory function has already profited from the operation of temperature sensors put close to the airways as well as from the sensorization of facemasks, widely used in case of respiratory viruses. In this paper, a UHF RFID temperature sensor tag integrating auto-tuning capability is integrated inside a FFP2 facemask to retrieve temperature profiles used to count and detect three different types of coughing. All the cough shots are consistently detected by the system, and their periodicity and duration can be determined.

This paper addresses the complete process of design, optimization, manufacturing and testing of a vector array of eight longitudinal slots, devised to work on the W band with a uniform amplitude taper distribution. Comparison between simulations and measurements are shown, revealing an almost perfect match in both radiation pattern and return losses.

In this paper, we present an all-metal antenna element with multiple feeding points for wide-scan angle arrays. The antenna element is composed of two slots feeding two stacked patches backed by integrated cavities. Dielectric material is used only in the feeding part of the antenna as a substrate supporting four asymmetric striplines feeding the slots. The radiating part of the antenna is built entirely from metal and air ensuring stable thermal behaviour of the antenna for high input power levels. The array supports wide-angle scanning up to a maximum of θ=60o for all φ-planes over almost ~16% bandwidth. The antenna element may find its application in the areas involving high radiated powers, e.g. communication systems, radar systems.

An ISM band sectorial compact antenna working at 868 MHz is presented in this paper. The antenna is designed to have very low perturbations in terms of radiation pattern, bandwidth and input impedance when mounted on different environments at the rear (i.e. wood, plastic or metal support). Furthermore, the PIFA topology of the antenna allows an easy matching either to a 50 Ohm input impedance for IoT/LoRA applications or to a complex impedance value for RFID applications with the help of a simple matching circuit.

This work presents an additively manufactured helical antenna for X-Band. A comparison between stereolithography and selective laser sintering processes is made. The proposed antenna concept includes a transition from the helix coil to an X-band waveguide, which allows for matching of the antenna to the waveguide. In our measurements, the proposed antennae featured a -10dB-bandwidth of 2.8 GHz and a -20 dB-bandwidth of 0.28GHz respectively. The suggested manufacturing and de- sign process is, therefore, a major step towards enabling complex antenna geometries.

In this work, additively manufactured pyramidal horn antennas are presented which are fabricated from UV-curable polymer resin by a DLP 3D printing system and subsequently coated by copper electroplating. In order to improve printing and metal plating quality, the models are adapted following the slotted waveguide approach and build orientation is discussed to cope with support of overhanging structures. The manufactured specimens reveal almost identical performance compared to a commercially available equivalent. This way, successful application of the slotted waveguide approach is demonstrated with horn antennas for mm-Wave frequency range.

This paper proposes a dual-linear polarized compact feeding system that generates surface waves with low transmission loss. The proposed feeding system is designed for compact size and dual-linear polarized characteristics by using pillbox structure, and the hologram pattern for generating surface waves. The feeding system obtained the transmission loss of -0.74 dB(lossless material), -3.41 dB(lossy material), and reflection loss below -10 dB from 21 to 27 GHz.

This paper discusses a novel PCB transition to feed an H-plane sectoral horn array intended for use with highly integrated mm-wave beamforming devices. To maintain the half-wavelength element spacing necessary for grating-lobe free operation, the signal launch into rectangular waveguide is oriented such that the waveguide 'b' dimension aligns with the PCB edge. The fabricated design achieves a good impedance match over a 14 GHz bandwidth centred at 64 GHz.

This work proposes a 4x4 double slot antenna array based on ridged gap waveguide feeding network for 39GHz. The antenna system is comprised of three independent layers. The top layer is the radiating layer with a 4x4 pair of slots configuration, the middle one is the resonant cavity, and the bottom layer involves the ridge gap waveguide. The use of pair of slots on the radiating layer achieves an alternative solution to radiating energy, as compared to previously published work, reducing the return losses and mutual coupling between the resonant elements, in the desired frequency operation. The presented design provides high gain and directivity over 18dB, due to the planar and multilayer structure, while the reflection coefficient is below -10dB over the operating frequency range 37.4GHz-40.2 GHz, covering a 7.2% bandwidth.

A dual circularly polarized (CP) slot array antenna is proposed for V-band applications. A sliding mechanism based on the groove gap waveguide is employed to achieve the left-hand circular polarization (LHCP) and the right hand circular polarization (RHCP). Due to the use of gap waveguide technology, there is no electrical contact between the different parts of the switch and the leakage of the electromagnetic wave is suppressed. The simulation results show that the proposed antenna has axial ratio (AR) below 3 dB, and pick gain of 14 dB in the desired impedance matching bandwidth from 58-62 GHz.

The aim of this paper is to investigate the steering mechanism of the beam pattern of a helical antenna using a half-cup plasma reflector. To this end, variations of the radiation characteristics and also the direction of the main beam of the antenna due to changes in the dimensions of the half-cup plasma reflector, including its diameter and height, are numerically computed and analyzed. The simulation results show that using this structure, the beam direction can be altered in 3-D space within a solid angle of ±10o. Also, it is highlighted that the half-cup plasma reflector may adversely affect the polarization of the helical antenna. Therefore, a trade-off between polarization and performance of an antenna based on a parametric study has to be made. Good agreement between the numerically calculated and measured results validates the presented study.

A high isolation and high gain antenna designed with polarization-dependent partially reflective surface (PRS) and polarization conversion surface (PCS) is described in this paper. It is observed that no matter what polarized source is employed, the final polarizations of the proposed antenna are identical. For demonstration, a dual-polarized square patch antenna operating at 9.0 GHz is simply employed as a TE- or TM-polarization source. The simulated results demonstrate the peak gains for two polarizations are all up to 14.4dBi, and the isolation between the two ports are more than 15 dB at 9.0 GHz. The experimental measurement results match well with the simulated ones verifying the effectiveness of the proposed antenna.

Next-generation weather radars are expected to be implemented with electronically-scanning planar phased arrays. Their scan agility could enable higher update rates and improved forecasts. However, application requirements on the polarization purity are hard to satisfy with a planar structure. Previous works in the literature have indicated a requirement of -22 [dB] on the Cross-Polarization Level (CPL) on scan under Ludwig's 2nd definition. This work presents a novel radiating element that approximates a magneto-electric dipole and has a printable planar structure. Preliminary numerical results show that the radiating element satisfies the CPL requirement in more than 98% of the scan directions of interest.

This paper introduces the DS-DMAS (double-stage delay multiply and sum) algorithm for 3-dimensional microwave breast cancer detection. In contrast to conventional confocal microwave imaging approaches, the DS-DMAS method performs the focusing twice which overcomes the limitations of conventional digital beamformers in terms of low image resolution and low contrast. This work presents image reconstruction examples based on numerical simulations with a comparison to DAS (delay and sum) and DMAS (delay multiply and sum) beamformers. Image analysis metrics have been implemented and discussed to quantitatively analyze the image quality. A significant improvement of DS-DMAS compared to both other techniques can be found.

In this paper, we investigate the gain switching performance of the software-defined radio USRP X310 with the TwinRX daughterboard and propose a method to optimize it for fast transitions. This receiver uses a complex structure of two switchable amplifiers and two digital step attenuators to realize the wide gain setting range of up to 92 dB. Our measurements of the settling time show that the bulk of transitions between two gain settings take below 1.5 µs, but some require more than 50 µs, caused by the power-up of the switchable amplifiers. Based on this knowledge, we propose a modified switching regime, in which the amplifiers are not toggled in time-critical phases, e.g., during a running measurement, so that a transition time of 1.5 µs can be reliably realized. Thus, a gain switching range of 62 dB is achieved, within which, for example, a fast automatic gain control can be realized.

Millimeter wave (mmWave) coverage is relatively limited due to high path loss (PL), that makes radio frequency planning difficult especially for the non-line-of-sight (NLOS) scenarios. In this work, we are looking to improve mmWave signal coverage in NLOS indoor scenario using passive reflectors. Measurements have been performed in L-shaped hallway using a vector network analyzer (VNA) and the path loss is evaluated with and without reflector. Experimental results show that in the presence of the passive reflector, the path loss can be reduced up to 24 dB. This type of configuration could be an economical solution to expand the mmWave coverage area. Moreover, a study is provided to compare the path loss when the reflector is placed horizontally to the path loss obtained when the reflector was placed vertically.

Current HF communication systems use sequential probing and scanning of narrowband (typical 3kHz) channels and transmissions in a single frequency band resulting in low efficiency.. In this paper we extrapolate the ideas in the HF-XL("Salamandre")-system and study a system where both the ALE and transmission procedures are fully parallel, i.e. channel probing and data data transmission can occur simultaneously in many channels on many available bands ("Channel aggregation"). An interesting problem is how distributed spectrum management for multiple links can be done in a meshed HF-network. We propose the simple "Constrained Greedy" channel allocation schemes and study the performance of a sample network in terms of throughput and message delay for various time-of-day and seasons. Result indicate that performance improvements up to an order of magnitude are possible compared to conventional systems. Finally, implementation aspects and constraints are discussed.

In this paper a simple deconvolution process for angle of arrival (AoA) retrieval is applied in a environment composed of up to five metallic poles to mimic a cluster of scatterers in the vicinity of the receiver. A measurement campaign was performed inside an anechoic chamber in two different configurations and a deconvolution process is applied to the measured signal. Preliminary results at K-band show that the proposed technique can be used to effectively retrieve the angle of arrival in a controlled environment as well as the relative power between the direct and the reflected components, that are of most importance for angular spread evaluation so that the refinement of existing and new propagation models can be achieved. In future works the algorithm will be tested within a polarimetric modelling of the propagation channel and will also be used to obtain the angular spread (AS).

Microwave hyperthermia as therapeutic modality in oncology can be the next breakthrough technology if translated properly to the clinical practice. For deep-seated tumors such as bone cancers, antennas and radiating sources fails in achieving therapeutic temperatures without overheating healthy tissues. In this framework, magnetic implant to be used as thermoseeds exposed to a several kHz magnetic field were studied. So far, the possibility of using magneto-dielectric biocompatible implant for performing microwave hyperthermia was not studied. In this work, we propose a simplified monodimensional electromagnetic model to study the propagation in a multilayer structure by means of the wave-amplitude transmission method. The model is aimed at finding suitable properties of the bolus, to be used as matching medium, while determining a set of working frequency. Then, we investigate the temperature evolution to determine, preliminarily, the feasibility of this innovative treatment modality.

A method to obtain the three-dimensional (3D) model of a hand for an antenna-hand interaction analysis of a mobile phone is presented. The radiation and reception performance of millimeter-wave signals is more susceptible to intervention by a user's hand than that of legacy below-6 GHz radios. Hand models representing a wide range of natural handgrips of mobile phone users are therefore essential. The 3D modeling is based on the photogrammetry using a video footage of a hand. Multiple 3D models of natural handgrips can be obtained with reasonable efforts. The radiation performance of a canonical antenna array implemented into a mobile phone sized chassis is evaluated using a developed series of 3D hand models, showing the uncertainty of repeatable antenna-hand interaction analyses.

Fat intra-body communication (Fat-IBC) is a novel concept of communication through the low-loss fat tissue layer of the body. This new data transmission approach is promising for the implementation of wireless, in-body, bidirectional Brain-Machine-Body connectivity, which will profoundly impact different fields, such as brain implants with read/write capability and human-like artificial sensors and limbs. In this paper, we apply an evolutionary algorithm combined with a full-wave electromagnetic solver to optimize a flat epidermal antenna, to improve the radiation coupling into the body and favor the signal transmission in the subcutaneous fat layer. The application of this method to a skin-fat communication channel shows satisfactory results when both the antennas of the link are considered and materials with high relative permittivity are used. A good radiation coupling into the body is observed, and transmission losses lower than 5 dB/cm are achieved.

In this paper, a circular polarization based wireless power transfer system is proposed for implantable medical devices (IMDs). Initially, a sequentially rotated left-handed circular polarization (LHCP) array operating at 2:4 GHz is designed for transmitter. Similarly, for receiver a miniaturised LHCP implantable antenna is designed inside a skin box to develop the WPT link. To improve the power transfer efficiency (PTE) of the WPT link a parasitic patch is placed near the receiver antenna. Parasitic patch improves the transmission coefficient by 8 dB thereby increasing the PTE by 6:7% for separation distance of 100 mm between transmitter and receiver. It is also verified that the proposed WPT system is insensitive to the angular rotation and lateral shift of the transmitter while keeping the receiver stationary. Finally, the specific absorption rate (SAR) of the implanted device is evaluated to ensure the safety limits of the proposed system.

Modular, passive and static metasurfaces are employed for the realization of a smart electromagnetic skin, a device embedded in the facade of buildings aimed at improving the communication performances through the intelligent reflection of the signal towards otherwise "blind" areas. The proposed design methodology considers an admissible surface area on the building facade and divides it into tiles (i.e., the minimal sized building blocks of the smart skin). A binary multi-objective genetic algorithm is then paired to the analytical model of the smart skin to optimize its layout (i.e., the tiles position and number), in order to satisfy a desired field threshold inside specific areas under consideration in the urban scenario. The final result is a Modular Reflecting Smart-Skin (MRSS) design methodology capable of providing an entire set of solutions, each one offering a trade-off between the complexity of the MRSS and the coverage of the blind area.

The LoRa framework has been recently proposed to foster search and rescue (SaR) missions in mountain environments. The target to be rescued could wear a LoRa radio embedded in a safety helmet so that an unmanned aerial vehicle (UAV) can localize it based on the transmitted signal strength. However, radiohelmet-to-UAV links in a real mountain area have never been characterized. This paper reports measurements of the excessive aerial path loss (PL) seen by a UAV overflying a mountain canyon to derive an equivalent model with the final aim of applying signal-strength-based localization. The angle-dependent fitting well describes the excessive aerial PL, and, despite the iced canyon's walls, no significant seasonal difference in the PL is experienced.

In fifth-generation millimeter-wave mobile terminal communications, the user body blockage will significantly shadow the radiation pattern and severely affect communication performance. In this work, the antenna is moved on the mobile handset to find a suitable position to suppress the user shadow. The investigation is conducted with the user in data mode. The shadowed antenna power ratio (SAPR) and shadowed cumulative distribution function (SCDF) are used to characterize the user blockage. Both simulations with whole-body phantom and measurements with the actual user were conducted to validate the results to provide a large degree of repeatability. A significant improvement can be confirmed when moving the antenna to the top of the handset plane than the bottom. An average of 7dB in simulation and 5dB in measurement in SAPR can be improved. The proposed method can be applied in the 5G handset antenna construction to reduce the deterioration caused by the human blockage.

Pyramidal absorbers used in anechoic chambers are one of the primary components in the measurement and performance assessment of antennas. To achieve absorbers with predefined specifications, optimum design and best material selection is an indispensable requirement. The proper material for fabricating an absorber has often been selected based on heuristic and intuitive approaches. Here, we introduce a process to find the most suitable electromagnetic material properties for achieving a target performance in an absorber with certain geometry. The method is based on using full-wave numerical simulations to obtain lines of equal absorption in the complex plane for material permittivity at certain frequency points. By locating the permittivity of available materials in the obtained plots, the best material to fabricate the absorber of interest is found. The example of 60-inch absorbers is taken into account, and the best carbon loading for fabricating such an absorber is gained through the developed process.

In this paper, the trade-off between the quality of the plane wave spectrum synthesized in the test zone of the hybrid over-the-air (OTA) chamber and factors affecting the dynamic range of this measurement system is investigated. The hybrid chamber performance is compared to a plane wave generator (PWG) in free space. The performance evaluation is focused on the field radiated into the test zone (TZ) while maintaining its quality according to the 3GPP specification. It is demonstrated that good quality can be achieved for the synthesized plane wave spectrum.

This paper investigates the characterization and calibration procedure of the hybrid over-the-air (OTA) measurement chamber. We present a prototype of the hybrid chamber and analyze its capabilities to generate a plane wave spectrum in practice. A planar field scanner is used to acquire the embedded element fields of the chamber array for test zone (TZ) synthesis in post-processing. The repeatability of the field acquisition is evaluated. It is shown that the synthesized TZ meets the 3GPP specifications for TZ field variations for plane wave generators (PWG) in the presence of acquisition imperfections.

In wireless systems, the realised characteristics of antennas in their operational environment are of major interest. This is especially true for wireless remote-control systems in combination with unmanned aerial vehicles (UAVs). In this paper we discuss measurement-based evaluations of a commercially available multi-band long term evolution (LTE) antenna mounted to the fuselage of a UAV. In comparison to the same antenna operated without the UAV, we observe an impact on antenna impedance as well as shadowing effects caused by the geometry of the UAV. Both lead to a reduced performance of the antenna and subsequently a reduction in communication reliability and range may be expected.

This paper introduces a novel approach for the measurement of time averaged Specific Absorption Rate (SAR) for multiple emitting antennas. The proposed approach is based on the use of the phase information of the E-field phasor given by radiofrequency vector SAR measurement system, for the retrieval of the instantaneous input RMS power injected in the emitting antennas from a small number of SAR measurement points. The approach is presented for the case of two emitting antennas. Numerical validation was performed in the case of two dipole antennas radiating coherently at a single frequency.

Ray-tracing methods can be applied to evaluate the wave propagation in anechoic electromagnetic environments, in order to improve measurement concepts. The accuracy of the data obtained from such a chamber model depends crucially on the modeling of the microwave absorbers. Often the scattering off the absorbers is simplified by specular reflections, ignoring the actual direction dependent scattering properties of the absorbers resulting from their geometry, arrangement, and material. In this paper, the scattering of 18" absorbers with pyramidal and wedge geometries is analyzed and expected scattering patterns are described. Based on an existing shooting-and-bouncing- rays software, a simulation approach is introduced and used to relate the analytical findings with results of measurements of the angle-dependent reflectivity. In addition to the primarily specular reflection for wedge absorbers and scattering in many directions off the pyramidal absorbers, the results show that nearfield effects influence this scattering pattern, as confirmed by the simulations.

In wireless communication systems, in order to respond to the perception of risks related to electromagnetic field exposure and allocate radio resources, the estimation of the received power and exposure map is an essential task and a challenge. This paper proposes an algorithm for estimating electromagnetic field exposure maps using U-net architecture based on convolutional neural networks. The power map estimation is transformed into an image reconstruction task by image color mapping, where every pixel value of the image represents received power intensity. The designed model learns wireless signal propagation characteristics in a realistic indoor environment while considering various positions of the Wi-Fi access points. Results show that indoor propagation phenomena and environment models can be learned from data producing an accurate power map to measure the electromagnetic field.

Numerical dosimetry is an essential procedure in designing and optimizing propagating EM-devices that confirm to the recommended limits of Specific Absorption Rate (SAR). However, as frequencies go higher, the complexity of the computational problem increases substantially. Moreover, the high heterogeneity of the human body and the uncertainty in its tissues properties add to that complexity. Furthermore, as the numerical domain becomes very large, the impact of numerical dispersion becomes more visible leading to decrease the mesh-size even more. This article sheds some light on the 3D-simulation of such computational problems, and revisits the necessary mesh-size condition that ensures convergences and accuracy of results. Comparisons between FIT and TLM methods are presented to show the speed of convergence for both methods.

In the vision of smart railways, a seamless high-data-rate and dependable wireless connectivity both for communication and sensing will be required. It is of primary importance to generate realistic channel data in order to do properly all the application layer end-to-end tests for all the relevant use cases that will be enabled by these wireless systems in railways. In this talk, we identify the major challenges and present the state-of-the-art solutions towards realistic channels of smart railways, especially for high frequencies, such as the millimeter-wave and THz bands. Moreover, future research trends are pointed out towards a thorough understanding of the propagation and wireless channel characteristics to support the design and evaluation of future smart railway wireless sytems.

The study of stratified media, defined as layered configurations of material substrates, is of paramount relevance in many scientific and technological areas like Acoustics, Geophysics and Lightning. In Electromagnetics, the first treatment of these problems is due to Arnold Sommerfeld who, more than one century ago, solved the most basic of all stratified media geometries, i.e. the two semi-infinite media problem. In doing so, Sommerfeld developed the fundamentals of a mathematical method, which is now known as the spectral domain approach (SDA). After many decades of latency, the analysis of stratified media using SDA knew a strong regain of interest, due to the introduction of printed technologies (microstrip and striplines) and the development in the 70s of the first planar antennas. Nowadays, SDA is used in many other areas of Electromagnetics, like Ground Penetrating Radar, satellite-based Remote Sensing and Optics&Photonics. This tutorial will review the stratified media problem and its formulation through the so-called Sommerfeld Integrals. Some tricky points, like complex square roots definitions, the relevance of a ground plane at infinity and the existence of a Sommerfeld pole (and hence of a surface wave) will be discussed. Numerical techniques will be briefly discussed and used to illustrate some recent discussions in the literature about the behavior of electromagnetic fields as a function of radial distances and of elevation angles (radiation patterns).

In this talk the quest for the "final" expressions for the energy stored in a radiator is overviewed. First, the several forms of power and energy that have been defined and used in electromagnetics over the last 100 years are briefly summarized, and their most important characteristics are discussed. In a first step, frequency domain is considered. Starting from two power balance equations, a field based reactive energy is formally defined and compared to the numerous "definitions" already available in literature. Then the concept of recoverable energy is introduced. The differences with reactive energy are pointed out. Moving to time domain, it is possible to write unifying expressions generalizing the concept of reactive energy. It is shown that recoverable energy is just a special case for a specific current evolving in time. Illustrative examples are given where these energies can be used to solve practical problems. The paper clearly illustrates that the concept of stored electromagnetic energy is still not well-understood when a radiator is involved.

Advanced electromagnetic surfaces (AESs) comprise a spectrum of artificially engineered surfaces for manipulating the temporal and/or spatial dispersion of electromagnetic waves, and include structures such as reflectarrays, transmitarrays, frequency selective surfaces, polarizers, and most recently, metasurfaces / metagratings. The design of such surfaces can be separated into two steps: a macroscopic step, where the surface parameters required to achieve particular manipulations of the incident field are determined; and a microscopic step, where the geometric structure of the underlying unit cells or meta-atoms is determined to realize those properties. This talk will review recent developments in systematic design techniques for both steps. In particular, synthesis methods will be described for carrying out the macroscopic step, particularly for spatially-dispersive AESs used to implement specific radiation patterns. Subsequently, a variety of techniques for solving the inverse design problem associated with the microscopic step will be presented, with emphasis on recently developed techniques based on machine learning. A selection of AES designs developed based on the proposed techniques will be presented, including experimental demonstrators of several metasurfaces.

This contribution presents the design and preliminary results of an electromagnetic wave propagation experiment at G band. The research activity, resulting from the collaboration between Politecnico di Milano and the Huawei European Microwave Centre in Milan, focuses on the design, integration and installation of a custom G-band 325-m terrestrial link connecting two buildings in the university campus. The unidirectional link carries an unmodulated beacon signal at 261 GHz, which allows investigating with high accuracy the atmospheric impairments affecting the propagation of electromagnetic waves. To this aim, the signal attenuation, inferred from the received power, is correlated to the ancillary data measured by the collocated rainfall sensor. The preliminary results reported indicate quite a significant impact of precipitation, which needs to be further studied using the information on the microphysical properties of rainfall.

In this paper, we compare measurements of the millimetre-band propagation channel at 60 GHz using Fujikura prototype communications equipment in an indoor office environment with those obtained using a Keysight N9042B Signal Analyser and simulations performed using Ray Tracing techniques. Based on the IEEE 802.11ad standard, the Fujikura equipment establishes a wireless network to measure the 60 GHz propagation channel. Wireless Insite software has been taken into account to emulate the scenario, where the simulation considers the three-dimensional environment model and proper material electromagnetic parameters. The experimental and simulation results include the Received Power, SNR, and Throughput. We show that there is a good agreement between experimental and simulation results. In addition, we have also verified that the measurements made with a horn antenna connected to the Signal Analyser, present a worse behaviour when there is Non Line of Sight with respect to the results obtained with Fujikura equipment.

The 6th generation mobile communication system requires the realization of ultrahigh speed and high-capacity communication. To meet the diverse communication requirements of individual users, it is desirable to use the terahertz band for communication between user terminals and peripheral devices. For the design and evaluation of stable systems, it is necessary to clarify the propagation characteristics of the blockage loss. In this paper, we investigated the propagation characteristics of the blockage loss for the human body at frequencies up to 110 GHz. Based on the experimental results, we clarified that the characteristics of the blockage loss due to a part of the human body follow the existing model. In addition, the variation in the blockage loss for a stationary human body is attributed to differences in the propagation path length produced by slight movement of the human body, and an estimation method for such a range of variation is presented.

In this paper we investigate the impact of the use of Transmitting Reconfigurable Intelligent Surfaces (T-RISs) on the indoor millimeter wave (mmWave) radio channel characteristics. To this purpose, two measurement campaigns were conducted by employing a T-RIS array and a virtual cubic array (VCA). The multipath component extraction was performed to embed the TRIS based antenna pattern and evaluate the effect on large-scale parameters such as the path loss, delay and angular spreads.

In this paper, we investigate the reflection properties of different interior surfaces in the 92-110 sub-Terahertz (THz) band. The measurements are conducted in an indoor environment by placing the surface in a specular configuration between the Transmitter (Tx) and Receiver (Rx) and collecting a large set of data by offsetting the Tx and Rx in parallel to the surface. The measurements were performed using an Agilent N5230A Vector-Network-Analyzer (VNA). Particularly, we present a statistical analysis in the frequency domain to show how frequency selective each surface is and how constant this behaviour is across the whole data set. We introduce the Power-Delay-Profile (PDP) in the delay domain to characterize the multipath behaviour of the channel and calculate the RMS delay spread. The measurement results provide a good insight for future propagation work to be done for the development of future indoor communications systems at sub-THz frequencies.

Several services associated with Satellite on the move and 5G applications are populating the K and Ka frequency bands. Beam forming networks are crucial components for achieving the necessary beam flexibility and agility of these systems. Rotman lens is being widely investigate as cost-effective solution for overcoming the main limitations of other types of beam forming networks, namely bandwidth, losses, and size. One of the main design challenges is obtaining broadband transitions for the array and beam ports. In this work we used a standard K/KA double ridge (WRD180) for interfacing with the Rotman Lens. The main motivation for this choice is the wide bandwidth (K/KA band) and the avoidance of dielectric losses associated with microstrip implementations. We present a design capable of fully exploring the ridge waveguide bandwidth with wide beam scanning, outperforming previous works. The presented design consists of a 13x7 Rotman Lens with a scanning range of ±50 degrees operating between 17.3 and 40 GHz, validated through full-wave simulations.

In this work a synthesis technique for designing sparse phased arrays of large size is presented. The procedure is based on an iterative convex optimization algorithm, also known as compressive sensing, which is straightforward to implement and efficient in terms of computational cost. It is capable of producing a layout with a significant reduction of active elements for predefined performance. Due to its effectiveness, it can also be employed for the optimization of large arrays. The capabilities and versatility of the algorithm are illustrated by different case studies. In particular, the possibility to reduce by 45% the number of elements in a large array is shown in details.

This paper presents an efficient design of an SIW horn antenna array for upper part of the Ka-band. The array is formed by a corporate network in substrate integrated waveguide (SIW) technology which feeds eight SIW horn. Impedance matching between each SIW horn and the free space is carried out by using a SIW-to-air transition that efficiently matches with the rest of the antenna elements. The array feed is based on an end launch connector over grounded coplanar-waveguide (GCPW) technology that makes an efficient transition to SIW. The corporate network has two-by-two electromagnetic (EM) field splitting levels through the use of H-plane T-splitters and waveguide bends. Thus, an in-phase and equal power symmetrical array structure is achieved from 34 GHz to 41 GHz (18.6% of bandwidth). The simulated results present a high stable gain of 14 dBi in the H-plane along the whole frequency range.

A novel partitioning scheme based on Penrose tessellation subarrays has been proposed for phased array design. More in detail, the radiating elements of a phased array arranged on a regular and periodic lattice are grouped into irregularly-shaped tiles by exploiting the features offered by the aperiodic Penrose tessellation. The preliminary results reveal that the novel array architecture ensures a remarkale reduction of the Transmit/Receive modules without compromising the performance in terms of scan angle and peak side lobe level.

The paper deals with the diagnostics of realistic array antennas by exploiting phaseless measurements. Provided the number of faults is not small with respect to the overall number of elements, the proposed approach allows performing the diagnostics whatever the kind of radiating elements even if the measurement surface is located in the near-field zone. Despite the high non-linearity induced by the adoption of phaseless measurements, the underlying optimization problem can be cast as a Convex Programming one taking decisive advantage of the Compressive Sensing theory. Examples concerning 1-D array diagnostics are given for both cases of ON-OFF and phase faults.

A compact monopole antenna for ultra-wideband (UWB) and beyond applications has been proposed. The radiator is based on the monopole topology. The super-wideband behavior has been achieved using a combination of spline-based modifications applied to the driven element, as well as utilization of a tapered feed and a slot-modified ground plane. The electrical performance of the structure has been tuned using a numerical optimization algorithm. The proposed design features reflection below the level of -10 dB within 2.8 GHz to 30 GHz range, as well as a footprint of only 404 mm2. The proposed structure has been compared in terms of bandwidth and size with the state-of-the-art antennas from the literature. The numerical results are supported by measurements of the fabricated antenna prototype.

The metasurface inspired antenna chip developed by the KIT EOE Laboratory (MACKEY, RFID 920 MHz) is an electrically small antenna that is sufficiently robust to metal objects. However, there have been demands for miniaturization of the available model, which has a length of 200 mm at 920 MHz. Therefore, a new model called the MACKEY type H (RFID 920 MHz band) is proposed herein and is miniaturized to the size of a card. The type H antenna can extend the current path in a meandered manner through slits cut along the long sides of the grid plate. This paper presents the characteristics of the MACKEY type H antenna and its measurement results.

In this paper, a miniature frequency-agile antenna is presented. The antenna is of balanced structure, composed of a driven element fed differentially, and a parasitic loop element loaded with a varactor. The antenna maximum dimension is 28.8 mm, electrical size ka=0.3, designed to operate near 1000 MHz. A prototype is fabricated and measured to validate the simulated performances. The measurement results show continuous eight states tunable bandwidth of 5.05% at the central frequency 1010.5 MHz corresponding to -10 dB |S11| maximum-acceptable input reflection coefficient, and a radiation efficiency of more than 34% over the tunable bandwidth.

In this paper, an orthogonally polarized antenna with a small diameter and low profile is proposed for mobile communication. The proposed antenna is composed of a Halo antenna loaded with two parasitic elements as the horizontal polarization element and dipole and sleeve antennas as the vertical polarization elements inside the Halo antenna. The simulation results show that the proposed antenna with the sleeve antenna has a relative bandwidth of 6.9 % (VSWR ≤ 2) and an isolation between polarizations of about 30 dB within the operating frequency. In addition, the antenna diameter and height of the proposed antenna are 0.14λ0 and 0.49λ0, respectively, and a low profile orthogonally polarized antenna is obtained.

There are some challenges in effectively producing low frequency electromagnetic waves, such as the need of large scale antennas, particularly for submarine communications. Due to hardness and challenges of building low frequency antennas, some solutions are provided. Using acoustic wave is one of solution which is the most common alternative for low frequency electromagnetic waves. A new solution which is in the researching level, is known as Mechanical Antenna. This sort of antenna which enables us to propagate low frequency electromagnetic waves, has the advantage of being extremely small in comparison with common electrical antennas. Some efforts have been done on analyzing and testing this type of antenna in order to estimate the pattern and propagated power of mechanical antenna. In this paper, initially parameters affecting the power radiated in past researches has been investigated and a novel solution is provided in order to increase the propagated power.

Heart valve replacement is one of the most common life-saving surgery procedures. Although valve prostheses can restore heart functionality and life expectations, they often suffer from to structural deterioration that can lead to the failure of the implant. Conventional diagnostic tools include minimally invasive and operator-dependent examinations. Alternative remote monitoring approaches would be extremely useful for evaluating the valve status from outside the body and for early detecting possible failure events. In the framework of Health 4.0 this paper proposes a method to extract an antenna mode out of an aortic valve so that it can be provided with communication capability without any need of battery. By minimal modifications of the mechanical layout, the valve integrates an RFID sensing IC capable to passively, sample the temperature in the surrounding tissues and communicate with an external reader. Numerical simulations and early experimental tests demonstrate the feasibility of the communication link.

Abnormal breathing can be a symptom of an unhealthy status. Conventional diagnostic exams involve cumbersome and intrusive instrumentation that are overall uncomfortable for the user. Ultra High Frequency (UHF) Radio Frequency IDentification (RFID) devices, instead, enable non-invasive wireless monitoring of respiration by means of epidermal antennas with embedded temperature sensors. Two sampling points in the same device could be useful to independently measure the respiratory flow of the two nostrils, which are known to work differently. At this purpose, this paper proposes a two-channel flexible epidermal sensor for the bilateral monitoring of nasal breathing based on temperature measurement. It compactly adheres on the prolabium, and comprises two coupled T-match asymmetric dipole antennas whose ICs are placed at the exit of the nostrils. The sensor can be read up to 60 cm. Experimental tests on some prototypes demonstrated that, thanks to negligible cross-sensitivity of the two ICs' temperature data, the breathing rate can be accurately estimated independently for the two nostrils.

The viable and safe application of wireless power transfer for powering bioelectronic implants requires understanding the wave propagation in heterogeneous and dispersive media, the electromagnetic exposure assessment, and the optimum design of the system parameters to achieve a trade-off between efficiency and specific absorption rate levels. Therefore, based on the case study of a wirelessly charged deep-implanted pacemaker, a parametric analysis on the transmitter dimensions and electromagnetic properties is carried out to achieve such a trade-off. The results show that the system reaches the maximum efficiency without increasing SAR levels when the transmitter is composed of an electric source, an air-like substrate, and a superstrate matched to the wave impedance in the skin with a thickness of half the wavelength in this medium. Furthermore, this configuration is compared to a magnetic counterpart, and the reasons for its suboptimal performance are investigated in terms of near-field, reflection, and attenuation losses.

Radiofrequency finger augmentation devices (RFADs) are hand-worn systems based on the RFID (radiofrequency identification) that can sense the objects touched by the wearer while preserving the free-hand gestures. A pressure-sensing R-FAD could be useful for applications in physiotherapy, orthopedy, and even more with the upcoming Tactile Internet (TI) paradigm, which aims at extremely low-latency communications and the transmission of human senses through the internet. This paper proposes a pressure-sensing fingertip tag that is manufactured using a robust conducting thread. Following preliminary tests on a prototype, the tag was demonstrated sensible enough to swiftly detect small discontinuities of the human body, like the back-hand knuckles.

This paper discusses a method to improve the resolution of microwave biomedical sensors. Usually, the frequency response of these devices is relatively wide as compared to its ideal shape. Furthermore, only a finite number of its samples can be acquired in the measurement stage. Accordingly, to have an accurate estimate of the resonance frequency, high performance systems with high sensitivity are required. Thereafter, in order to overcome these drawbacks, an iterative algorithm is presented which aims at sharpening the microwave sensors response. The algorithm assessment is performed on measured data referred to a real scenario, which is inherent to return loss measurements of a microwave patch antenna submerged in a water-glucose solution with various glucose concentration levels.

A key issue facing the 5G Evolution and 6G eras is expected to be expanding the communications area to any place where its benefits can be enjoyed. To expand the communications area, we are focusing on implementing a communications area from the sky using satellites and a high-altitude platform station (HAPS). In particular for HAPSs, the use of broadband millimeter-waves is expected to enable the timely provisioning of the required high-speed high-capacity low-latency access in any location including at sea, in the air, or remote areas. Before using an actual HAPS system, we performed an initial experiment to measure the propagation characteristics in the 39-GHz band using a small aircraft. The experimental results assuming HAPSs in an urban area, a forest, and a remote island show propagation loss in the 39-GHz band in various environments under the influence of aircraft turning.

A reproducible semi-virtual test drive system for C2C/C2X-transmission is shown in its application on a new antenna diversity circuit at 5.9 GHz. The correct functionality of the system itself and the time-varying property of the output signal is verified. By help of this test drive system a new parallel sniffing diversity circuit is investigated. Due to the advanced circuit design, the diversity function is possible without the need of a cooperative receiver. Characteristic RF-functions of the RF-diversity circuit are explained and its performance in a typical driving scenario is shown. The antenna diversity shows a significant reduction in package error rate and moreover increases received signal strength.

This paper presents the study of a multi-layered timber barrier of periodically arranged logs with the purpose of enhancing the electromagnetic (EM) shielding or transparency to radio propagation through the fine-tuning of the barrier's parameters for applications in road electromagnetic barriers. Simulations were performed and analysed in 5.9 GHz band, where spacing between centre of wooden poles is parametrised in a EM simulation environment. Such tunable EM fence may find applications in roads where C-V2X communications are subject to high EM interference or low radio propagation exposures, which are intended to be controlled.

In this paper, the measured median pathloss between the ports of a pencil-beam antenna as a base station antenna near the railway track (i.e., antenna corridor), and a dipole antenna onboard a train wagon is presented. The selected wagon is an ordinary Swiss inter-city double-deck wagon recently equipped with RF-friendly windowpanes. Here our focus is the port-to-port median pathloss at around 3600 MHz band. The results highlight that the excess pathloss into the wagon compared to the line-of-sight free space pathloss with similar antennas is within the range 15-38 dB. We further address the polarisation pathloss imbalance present inside the wagon and quantify it. This imbalance is an outcome of the presence of non-rich multipath inside the wagons equipped with RF-friendly windowpanes. In the end, we show that the paths through the closest windowpane to the user equipment are likely the dominant ones and thus determining the pathloss.

Considering the fuselage posture and antenna pattern of unmanned aerial vehicle (UAV), a three-dimensional (3D) multiple-input multiple-output (MIMO) geometry-based stochastic model (GBSM) is proposed and the spatial-temporal correlations of UAV-to-vehicle (U2V) channel are studied. Based on the fuselage posture matrix and antenna pattern matrix, the temporal autocorrelation function (ACF) and spatial cross-correlation function (CCF) are deduced and investigated in detail. The simulation results show that variation of fuselage posture and antenna pattern has significant impacts on spatial-temporal correlations. In addition, the consistency of theoretical and simulation results verified the correctness of the proposed model and derivation.

This paper proposes a novel circular polarized microstrip array with high gain for satellite communication in X-band. In order to extend the impedance bandwidth, the novel single-feed unit element is created without adding the profile. The proposed antenna employs the sequential rotation technique to improve the axial ratio bandwidth with high circular polarization purity. The final design, with an overall size of 91.6 mm×45.8 mm×1.7 mm is simulated. The proposed antenna can provide an impedance bandwidth of 62.1% from 8.83 GHz to 16.78 GHz, and 3 dB axial ratio bandwidth from 9.84 GHz to 11.52 GHz. The realized gain at the center frequency is 16.4 dBi (with 3-dB gain in band ranging from 9.70 GHz to 12.18 GHz, covering the whole axial ratio bandwidth). Thus, the proposed low-profile circular polarized antenna is suitable for X-band satellite applications.

This paper presents a full-metal unit cell for reflectarray antenna. This unit cell has been designed to work in space environment and is versatile to a large range of frequencies from X-band to Ka-band. In this paper, An X-band 3-panel reflectarray for small satellite has been developed as an example of application. The size of each panel is 200x350 mm². The reflectarray has been designed for the [8-8.4] GHz band and shows a good stability on the band. The maximal gain is 28 dB and the half-power beamwidth is 8°.

Design, development, and measurements of X-band patch antennas for a CubeSat platform are presented in this paper. The challenge was in the design of circularly polarized patch antennas suitable for building an array since the goal is to achieve highest possible radiation efficiency. Therefore, six antenna designs were developed which can be differentiated by the number of PCB layers and by the method of excitation. Also, for achieving circular polarization two shapes were considered, a corner truncated square patch and a nearly square patch. The characteristics of the developed antennas were analyzed and measured showing the advantages and disadvantages of certain designs. Based on the analysis of measured results we reached guidelines that will be used further for designing the full X-band array.

In-Flight Connectivity services through satellite systems is expected to grow exponentially throughout the 2020 decade. The deployment of high throughput satellites and mega-constellations in low and medium earth orbits will result in higher demand and lower running costs. However, in addition to harsh environmental conditions, antenna systems must overcome important challenges derived from heterogenous scenarios and the associated regulations. This paper focuses on these aspects and proposes smart apertures based on electronically steerable antennas to enable multiple beam and fast steering capabilities and to mitigate the restrictions of emission in the geostationary arc.

In small volume instruments, such as CubeSat spacecraft, the realization of wideband THz spectroscopy instruments is challenging, since a practical antenna gain typically results in a large antenna form factor or small bandwidth. In this work, a low-profile submillimeter-wave lens antenna, operating over a broad, 20% fractional, bandwidth from 450 GHz to 550 GHz, is presented with a gain of 50 dB and aperture efficiency of 65%. A multi-layer leaky-wave stratification is synthesized to efficiently and uniformly illuminate a 7.4 cm diameter hyperbolic silicon lens over a wide angle, resulting in an overall antenna height of only 3 cm. The antenna is fabricated and currently in its measurement stage. Preliminary measurements in the WR2.2 frequency band are presented.

The results of the study of the large deployable reflector antenna for a SAR study project being conducted for the European Space Agency are presented. The antenna is fed by a large feedarray, and the effect on the antenna patterns of the different feeders are shown. Comparison between the ideal antenna surface and its deployable configuration are presented. An initial study of the rms errors of the deployable antenna configuration is presented.

Future applications in sensing and communications will benefit from having large integrated coherent arrays at THz frequencies. The use of lens arrays will enable the fabrication of integrated antenna front-ends with many potential independent beams as well as dynamic scanning capabilities. For certain types of applications such as MIMO communications, interferometric arrays and Tx/Rx duplexing capabilities, a key parameter is the mutual coupling between the integrated antenna front-ends. In this contribution we model such mutual coupling using PO techniques combined with a bi-directional forward ray-tracing, and compare its accuracy to full wave simulations. The proposed technique is then used to evaluate the mutual coupling for an example lens array architecture. A more complete study comparing several lens array architectures will be presented in the conference.

This paper presents the design and optimization of a transmit-array (TA) operating at 10 GHz. This TA is based on a new Unit-Cell that allows to easily generate phase rotations required for TA design, while keeping insertion losses to a minimum (0.3 dB) and a relative working bandwidth of 9% at 10 GHz. The proposed unit-cell is a simple three metallic layer structure, in which two identical patches are interconnected through an inner via. The optimized structure has a low profile with a total thickness of 3.2 mm. To demonstrate its performance, a 1-bit transmit-array with 20x20 cells is simulated and manufactured showing a high gain of 21.01 dBi and low side lobe levels (-20.93 dB). Finally, to reduce its overall profile, a multiple feed TA is conceived using an particle swarm optimization algorithm to define the phase compensation distribution and allow a reduction of 50% of the focal length.

This work provides an assessment in terms of computational speed and accuracy at the radiation pattern level of a database to characterize the reflectarray unit cell for use in analysis, layout design and crosspolar pattern optimization. Details of an efficient implementation of the database are provided, and its performance is compared to that provided by a machine learning technique based on support vector regression (SVR). A method of moments based on local periodicity serves as the baseline for the comparison, both in terms of accuracy and acceleration. The results show that, even when the database uses a simple N-linear interpolation, accuracy is similar to that provided by the SVR technique while accelerating the analysis and layout design of reflectarray antennas.

A high gain slot array antenna with 5 waveguides and 60 elements is proposed. The antenna is balanced fed by a sectorial horn. The antenna is matched for VSWR = 1.8 between 9.7 to 10.7 GHz. The directivity of the antenna is between 22 to 24.5 dBi with low loss. The antenna can be easily optimized in the E-plane and in the H-plane beamwidths.

In this paper, we present the design of a reconfigurable transmitarray operating in the D-band. The transmitarray unit cell has a relatively simple structure with three metal layers and two quartz dielectric substrates. The active transmitting patch of the unit cell ensures a 1-bit phase shift resolution by alternating the states of two innovative switches. Here, we overcome the small dimensions challenge in the D-band by introducing compact switches that are compatible with the dimensions of the proposed unit cell. The switches are made of phase change materials that alternate between the amorphous and the crystalline states under the effect of heat. We present a full-wave simulation of the unit cell, which shows an insertion loss that is below 1.5 dB over a relative frequency band of 27%. Furthermore, we synthesize a 16×16 elements transmitarray using an in-house MATLAB tool and compare its theoretical results to a full-wave HFSS simulation.

This paper presents a circularly polarized dual-band shared aperture antenna for satellite applications. The antenna achieves dual S- and Ka-band operation by housing both a circularly polarized high-frequency reflectarray and a circularly polarized low-frequency patch antenna array in the same aperture area. The high-frequency reflectarray part of the antenna has unit elements within the aperture area of the low-frequency patch antenna array which allows for a high realized high-frequency gain. The antenna has a layered structure with a middle layer of Polypropylene, this enables the low-frequency part of the antenna to achieve a wide impedance bandwidth and a high realized gain. The antenna has a total size of 136x136mm and the three layers of the reflective surface have a total height of 4.624mm. The antenna has an impedance bandwidth of more than 415MHz(12%) and 4.75GHz(19%) and a peak realized gain of 14.80dBi and 26.68dBi at 3.5GHz and 25.4 GHz, respectively.

A metal-only reflectarray unit cell to independently control two polarizations is proposed in this paper. The unit cell is based on a nonresonant cross-shaped geometry backed by a metallic plate. Unlike previous metal-only nonresonant unit cell, the metallic arms of the proposed one are not connected to its neighboring unit cells. This fact enables the propagation of the incident wave along the longitudinal direction of the unit cell more specifically, along parallel-plate waveguides formed between unit cells. Depending on the polarization of the impinging wave, the propagation occurs in the waveguides located at vertical or horizontal directions. The simulated results for a designed unit cell at 60GHz show the independent modification of the phase response for one polarization being unaffected the phase response of orthogonal one. Moreover, phase linearity and a phase shift range over 360o are achieved along a operating frequency range with good phase stability under oblique incidence.

This paper presents the development of a reconfigurable vanadium dioxide (VO2) based reflectarray antenna using a novel 1-bit split patch element. The thermally actuated unit cell, composed of a quarter wavelength copper patch and a VO2 thin film switch is able to achieve 180° of phase at 35 GHz with a maximum loss of 0.35 dB. Such a design exploits the reversible metal to insulator transition properties of VO2 at 68 °C. The simplicity of such an element provides a low cost practical reconfiguration strategy that can be extended to large apertures. A full-wave 40 × 40 element simulation of the switchable device demonstrated a maximum gain of 21.1 dB at 0° and 1D beam scanning performance covering - 60° to +60° with a 4.5 dB reduction in peak gain over the full scanning range.

A dual-polarization reflectarray cell backed by a frequency selective surface is proposed for the design of coverage-enhancing panels in 5G networks at the 28 GHz band. The FSS-backed reflectarray cell suppresses the undesired reflections of impinging signals which propagate at the frequencies of other mobile communications systems, such as the sub-6 and 39 GHz bands of 5G. Several FSS topologies have been evaluated for the design, seeking to get the structure to behave as a metallic ground plane at the 28 GHz band, while being transparent at the sub-6 and 39 GHz bands. The reflectarray elements have been placed on top of the FSS, and the performance of the FSS-backed reflectarray cell has been compared with that of a conventional reflectarray cell backed by a metallic plane. The simulations confirm the potential of the proposed structure to design reflectarray panels with suppressed out-of-band reflections to enhance coverage in 5G systems.

This paper presents a comparative study of different antenna array architectures for achieving ultra-fast Point to Point wireless links for potential use in future 6G backhauling applications. This study analyzes both focal plane and phased array architectures that can lead to higher throughput via Multiple Input Multiple Output architectures. It is found that to reach ultra-fast and radiated energy efficient Point to Point (PtP) wireless links, the antennas should exploit the multi-mode capacity of radiative near-field links. The study presents the theoretical achievable capacities based on the channel matrix estimated in the radiated near-field and the application of the Shannon formula. The study focuses in the 220-320GHz spectral bandwidth defined by the new IEEE 802.15.3d standard and reports the curves versus the link distance. It is found that capacities well above Tbps can be theoretically achieved, even without the use of interference mitigation techniques.

This paper proposes a novel full-wave methodology for estimating the channel state information (CSI) in massive multiple-input multiple-output (mMIMO) applications. Our approach is based on a hybrid implementation of the shouting and bouncing rays (SBR) and finite-element (FEM) methods. Numerical simulations using FEM are carried out for designing a patch antenna, which provides 1.15 GHz bandwidth centered at 26 GHz and 7.5 dBi gain. The antenna is used to represent the user equipment (UE) and the antenna array element of a base station (BS). The antenna results are imported into the SBR solution region as linked sources. The chosen scenario is the Research Laboratory WOCA from Inatel (Brazil), with a 91-m² area, concrete walls and furniture made of wood and metal. Numerical SBR simulations are presented and a 16-order MIMO channel is successfully estimated in terms of magnitude and phase.

Orbital angular momentum (OAM) can provide an additional multiplexing degree for millimeter wave multiple-input multiple-output (MIMO) communication. However, the performance of OAM link will suffer a great loss in non-ideal propagation scenarios, i.e. misalignment and incomplete receiving UCAs, since the divergence of OAM waves. In this paper, a partial receiving and beam steering scheme is proposed to improve the performance of millimeter OAM-MIMO link. While the beam steering scheme can direct the OAM beam to the receiver area, the partial receiving scheme can derive the complete receiving matrix by partial antenna array elements and demultiplex OAM signals. Numerical results show that the partial receiving scheme based on beam steering greatly improves OAM propagation and the system capacity.

This paper proposes a 2x2 MIMO microstrip patch antenna for application in the ultrawideband frequency range. The design makes use of a metamaterial structure to enhance the isolation (S12/S21 parameter), keeping it well below -20dB. The impedance bandwidth of the proposed MIMO is from 2.06 GHz to 15.21 GHz, encompassing the entire UWB bandwidth. The proposed antenna's performance has been validated by measuring five MIMO diversity parameters throughout the impedance bandwidth. CCL is < 0.2 bps/Hz, DG is nearly 10, ECC is < 0.0014, TARC < -10 dB, and MEG stable around -6.25 dB. The overall dimensions of the proposed antenna are 89mm x 30mm x 1.6mm.

This research study proposes a 3.5 GHz array system that demonstrates a hybrid combination of beam-forming and beam-switching schemes. As basic antenna element, a printed ESPAR antenna is employed, with capability to direct its radiation pattern by means of PIN diodes switching. Furthermore, the antenna element impedance matching technique is investigated. Consequently, a four element ESPAR antenna array (MuPAR) is formed in order to exhibit the beam-switching operation of the elements, in combination to the beam-steering technique through a phase shift on the array elements. As a result, a novel hybrid beam-forming array system is implemented, demonstrating multiple scanning capabilities.

The establishment of 6G networks is being actively pursued worldwide. 6G will require extremely high-speed and high-capacity communications exceeding 100 Gbps, and one solution is to utilize new frequency bands above 100 GHz. However, specific new radio- interface technologies and service frequency bands have not been determined yet, because propagation characteristics above 100 GHz in various environments have not been studied sufficiently. In consideration of exploiting new frequency bands for 6G, path-loss characteristics from the microwave to sub-terahertz bands in an urban microcell environment were investigated. Also, the dominant paths that affect the path-loss characteristics were clarified on the basis of the measured power angular profiles.

An approach to estimate a radar cross-section (RCS) of a tree through numerical simulations is studied. This paper covers bare trees with a trunk and branches and without leaves. Recent advancements in three-dimensional (3D) modeling of trees and electromagnetic solvers allow simulation of field scattering from a whole tree. There are open issues in performing the simulations: 1) obtaining 3D models of tree trunks and branches, especially whether they have to be multi-layered or not; 2) knowing dielectric parameters of tree trunks and branches, especially for higher frequencies than 10 GHz; 3) using a right field solver depending on the electrical size of a tree. We propose suitable 3D models of tree trunks and branches, show our present knowledge of dielectric parameters of living trees, and finally demonstrate impacts of branches in addition to a trunk on the estimated RCS through numerical simulations at 1000 MHz to 0.1 THz.

High-capacity bandwidth makes sub-THz spectrum a key element of beyond-5G or 6G networks. However wireless communications at frequencies such as in W-band, D-band or above do suffer from strong constraints at the physical layer, they may be greatly beneficial for adequately chosen ultra-broadband applications and network topologies. Multi-hop backhauling and Fixed Wireless Access (FWA) networks are both candidates that we decided to assess as a combination. The physical-layer performance is estimated from LiDAR-based ray-tracing predictions and by considering a sub-THz polar-QAM modulation. The site placement is optimized by an automated heuristic method. Finally, analysis of a case study in a North American residential area demonstrates that a FWA design at 150 GHz is challenging due to propagation, but feasible. The comparison between a coverage-constrained sub-THz design and a capacity-constrained 5G design shows interesting complementarity.

This paper presents an overview of the vector network analyzer (VNA)-based phase-compensated channel sounder at sub-6 GHz, mmWave and sub-Terahertz (sub-THz) bands. The optical cable solution can enable long-range channel measurements for all these three bands, since it can effectively minimize the cable loss. The phase compensation architecture and principle are also discussed in this paper. The phase compensation scheme could stabilize the phase change introduced by optical fiber of the channel sounder to enable accurate phase measurement, which is essential for application in multi-channel/antenna measurements. We summarized the performance of the designed channel sounder under two types of cable effect condition, namely thermal changes and mechanical stress. Under these two cable conditions, the phase compensated channel sounders are validated in back-to-back measurements. The compensated phases demonstrate the robustness and effectiveness of these channel sounder for the frequency bands of 1-30 GHz, and 220-330 GHz.

In the present paper we introduce the empirical results of measurements with an over-the-air based propagation artifact for verification and validation of sub-THz and THz channel sounders and parameter estimation algorithms. This experiment produces a fixed number of multipath components with traceable propagation properties in the different domains that can be used to test resolution and performance. Because of the inherent characteristics of the measurement hardware, we have introduced an adaptation on a parametric high resolution estimation algorithm to account the imperfections of the channel sounder. The results have shown to account for a relative good performance of the sounder and the tested parametric and non-parametric estimation algorithms.

The sixth-generation wireless communication research activities were launched worldwide. A tendency of some researchers to use the sub-terahertz frequency band for 6G is noticed. This frequency band is selected as a candidate for 6G due to its remarkable wide unused frequency bandwidth. In this paper, typical indoor environment material transmission measurements from 2 GHz to 170 GHz are presented. These measurements aim to further understand and compare wave-material interaction for above and below 100 GHz frequencies by providing a continuous measurement up to 170 GHz of 16 different materials e.g. glass, plasterboard, concrete, and wooden materials. The measurement system is based on a vector network analyzer, with frequency extension modules for frequencies above 50 GHz.

A need for measurement data for frequencies above 100 GHz has increased. In this paper, we present the measurement system for millimeter wave frequencies (30-300 GHz). It is based on Keysight PNA-X vector network analyser with frequency extenders mounted on custom built 3-axis rotation stages (both the transmitter and receiver sides). We present some initial results from measurements conducted in an office corridor. Both line-of-sight (LOS) and non-LOS (NLOS) cases are included in the measurement set-ups. The results show that in all cases the channels are sparse with clear clusters from large reflecting surfaces, such as walls and floors. The measured power levels are rather strong indicating relatively low reflection losses. While the channels were sparse, there were still typically relatively large numbers of distinguishable paths. The numbers of observable paths as well as the delay spread of the channel increase with increasing beamwidth.

This work presents an empirical indoor sub-THz channel characterization. The frequency aspect is studied through measurement campaigns conducted for different frequency ranges: 125-155 GHz, 235-265 GHz and 270-300 GHz, allowing to compare the channel of the D-band range with the channel above 200 GHz. Two different laboratory scenarios are taken into account. A double steering of the antennas at the transmitting and receiving side allows to perform a double angular characterization. The multipath components detection results are provided and path loss and delay spread models are reported. Finally, a clustering of the detected paths is also presented.

In this paper, we compare radio propagation channel characteristics of the 28, 60 and 140 GHz bands in one indoor and one outdoor hotspot scenario. The paper concludes that the excess loss, i.e., the loss in addition to the free-space path loss, is very similar for 28, 60 and 140 GHz as long as the measurements are conducted in open areas or where only one or two reflections are needed to get coverage. In areas requiring multiple reflections or wall penetration to achieve coverage, the excess loss increases for the higher frequencies.

Due to the large available bandwidth, wireless communications in the THz range are foreseen to provide high data-rate transmissions. Compared to transmissions at lower frequency ranges, wireless communications in the THz range are inherently more robust against eavesdropping attacks due to their propagation characteristics such as a high free space path loss. It does not connote, however, that eavesdropping is not possible. In this paper, ray-optical methods and confirming channel sounder measurements at 300 GHz are used to show that even common, ordinary features such as door frames or a TV screen in the selected meeting room scenario can have a significant influence on the wave propagation at 300 GHz. Thus, such objects can provide opportunities for eavesdropping signals even at unexpected locations outside of the main lope of the antenna diagram and behind the transmitter and cannot be neglected.

A near-field resonant parasitic (NFRP) active electrically small transmitting antenna is reported in this paper. It consists of an electrically small NFRP antenna and an operational amplifier (OpAmp). In the design, the NFRP element serves as the main radiator and the feedback pathway of the OpAmp simultaneously. This configuration significantly increases the effective gain of the electrically small antenna (ESA) without consuming any additional real estate. The overall electrical size is extremely small with ka = 0.15. The measured results of this active ESA, in good agreement with simulated values, demonstrate its effective gain can be dynamically tuned within a 6.01 dB range. Compared with its corresponding passive counterpart, the measured maximum effective gain and hence, the effective isotropic radiated power (EIRP) of developed active ESA witnesses 9.152 dB (8.23 times) improvement. Thus, the measured gain-bandwidth product (GBWP) surpasses the corresponding passive Bode-Fano upper bound by approximately 15.2 times.

Additional antennas are needed in smart phones to support 5G bands. The metal rim, which is the most attractive position for antennas, is already fully occupied by antennas supporting legacy bands. Therefore, there is a growing interest in new, more challenging antenna locations, such as the back cover of the phone. In this paper, we introduce a dual-polarized frequency reconfigurable wideband planar multiport antenna to the back cover of a mobile phone. The antenna has a height of only 0.5 mm. The simulations show that the introduced antenna achieves better than -5.8 dB efficiency from 3.3 GHz to 4.2 GHz.

This paper presents a design of water-based flexible, optically transparent and frequency reconfigurable antenna having a unidirectional radiation pattern. The proposed antenna incorporates a dipole radiator on top of a reflector plane that makes the radiation unidirectional. The reflector is constructed from pure water enclosed inside a circular cavity made of polydimethylsiloxane (PDMS), which consists of several ring chambers arranged concentrically. Frequency tuning operation is achieved by an innovative mechanical tuning mechanism involving controlling the water configuration inside the circular cavity. Depending upon the presence or absence of the water in different chambers, the resonance frequency changes accordingly while maintaining the radiation pattern unidirectional. Detail simulation investigation of the proposed technique is presented in this paper.

This work proposes compact multiport antennas for directional modulation (DM) on wrist-wearable devices to improve the secrecy and privacy of the transmitted data. The DM performance is investigated using the antenna in free-space and with a human forearm-phantom. The system achieves a low Bit Error Rate (BER) < 10^(−1) with 54° beamwidth, in a unique steerable secure direction over the entire azimuth plane. Full-wave simulations, including the phantom at 5 GHz, show realized gains of up to 4.26 dBi. The specific absorption rate is below the standard limits, with maximum values of 0.487W/kg and 1.42W/kg for the wrist-worn and next-to-mouth conditions, respectively.

Mutual coupling between antennas is a key parameter in multi-antenna systems. The present paper describes a method to map contributions to the magnitude of the mutual coupling spatially on surfaces between the ports. The method utilizes the reaction theorem for electromagnetic fields to obtain the contribution of the coupling from different regions. The derived result is valid for and applied to the strong-coupling regime, where the mutual impedance is of the same order as the self-impedance.

A new wideband and miniaturized metal rim antenna is developed based on a frequency-variant material for smartphone applications. The proposed antenna has a small clearance of 2 mm and uses a simple feeding method without impedance matching networks. This compact antenna, like a small module, can be designed at the top side of the substrate without extending to the long side which will reduce the user hand effect significantly. Three cases with/without new material are investigated and compared to demonstrate that the proposed antenna based on the new material is a good candidate for modern smartphone antenna applications.

This paper presents a network characteristic modes based method for parasitic superdirective arrays matching. The proposed method is used for designing a two M-monopole array with a separation distance of d=0.1λ. that achieves a near 50 ohm input radiation resistance, resulting in a matched input impedance, and therefore, a substantial increase in realized gain or total efficiency. The designed array shows a maximal directivity of 7.37 dBi and an impedance bandwidth of 23 MHz. The array present a -1dB bandwidth of directivity, gain and realized gain respectively of 70 MHz, 70 MHz and 31 MHz.

In this paper, a highly miniaturized folded slot-based multiple-input-multiple-output (MIMO) antenna design is presented for Cube Satellites (CubeSats) applications at UHF band. It consists of meandered slot structure folded on both sides of the substrate board. Miniaturization is achieved using a unique combination of meandered slot with folded structure along with reactively loading using a discrete capacitor. The antenna exhibits wide-band operation covering frequency bands from 430-510 MHZ. The proposed antenna is best suited for small satellite especially for CubeSat applications. The proposed antenna design has a total board dimensions of 100×100 mm2.

Beamforming for an antenna array using a modal technique is presented. The approach is suitable for the antenna array consisting of arbitrary elements in any mutual arrangement since its full-wave characterization is employed. The technique is demonstrated on an example of a planar antenna array with linear polarization.

Attaching a dipole antenna to dielectric material of largely different permittivity leads to strong variation of antenna feed impedance. The performance of a connected transceiver may deteriorate drastically. The proposed antenna provides three feed-points, which show respective feed-point match to 100 Ohm balanced feeds for three different dielectric environments (free-space and half-spaces of permittivity 4 and 42, respectively). The antenna is compact and implemented into a mechanically flexible foil. The three feed-points are very close to each other to accommodate a single RF chip. The antenna design for frequency of 5.5 GHz is supported by measurements, which agree well with simulations.

This paper proposes a bio-degradable antenna design well-suited for the 5th generation (5G) wearables. This antenna has a graphene patterning instead of conventional metallization on a textile substrate to make it eco-friendly as it avoids copper corrosion due to repeated washing of the wearable garments. The antenna design incorporates coplanar waveguide (CPW) feeding and directive stubs to converge the radiation pattern. The antenna patch footprint is reduced by fitting the radiating length into a small area by inserting the cut-outs through an iterative design process. The proposed antenna offers a bandwidth that covers the proposed newly launched 5G band (i.e., 3.4-3.8 GHz) with a resonant frequency at 3.55 GHz, realized gain of 4.11 dB, and an efficiency of 83%.

Monitoring of the breath rate is important for assessment of patients' health condition, sleep quality, sports monitoring, operational health, safety and early detection of potential serious respiratory system infections. Despite the need for continuous respiratory rate (RR) monitoring, wearable RR sensors are highly demanded in the relevant application fields. In this article a wearable breath rate sensor based on a planar spiral resonator (SR) is presented. The SR is accommodated on a textile substrate allowing the sensor to conform to non-planar surfaces making it suitable for integration in garments. The respiration rate is retrieved by using the SR and a wireless reader probe placed close-by. The working principle is based on tracking the movement of the chest wall or abdomen during respiration. The proposed device is can measure the respiration frequency by analysing the modulated signal at the probe. The sensing concept was verified experimentally using a breath simulator.

One of the challenges in development of body-centric communication and sensor systems is to design wearable antennas that are technically and aesthetically acceptable to be worn. This paper describes a novel wearable antenna design

• textile realization of slotted waveguide antenna. In order to characterize the proposed antenna solution, the measured antenna parameters were compared with the parameters of the equivalent antenna made from aluminium. The realized antenna is suitable for realization of off-body communication mode and can be integrated into clothing, e.g. as a smart belt.

Boluses with biotelemetry capabilities enable wireless monitoring of animal physiological data (ruminal temperature, pH). These devices rely on antennas to interface with external receivers. Existing antennas typically provide a short-range (1-2 m) communication, which can be improved by addressing the radiation efficiency. In this paper, a novel design approach for in-body antennas for animal biotelemetry applications is presented. The optimal frequency band is studied prior to the design of the antenna based on the dielectric measurements of the antenna environment. A demonstrator conformal patch antenna is proposed for the 434 MHz ISM band. The performance of the antenna is simulated in phantoms with cow's rumen fluid electromagnetic properties. The antenna is integrated in a bolus with 13 cm length and 1.5 cm radius. The proposed antenna has a gain of -20.1 dBi and the radiation efficiency of 0.53% in a spherical phantom with a diameter of 200 mm.

A wearable wideband textile patch antenna with two parasitic shorted strips for off-body communication is presented. The antenna exhibits excellent mechanical resilience thanks to the highly flexible polydimethylsiloxane (PDMS) substrate and textile conductor. The two parasitic shorted strips are introduced to create a new resonance which significantly widens the overall antenna bandwidth. A stabler broadside radiation is generated over the operation frequency from 5.4 to 6.0 GHz for off-body communications, covering some 5 GHz Wireless Local Area Network (WLAN) bands and the 5.8 GHz Industrial, Scientific, and Medical (ISM) bands. The antenna design is fabricated and experimentally validated, the good agreement between simulation and measurement suggests that the proposed antenna is promising for off-body communications.

Future railway applications, e.g., wireless train bus or virtual coupled trains, will rely on train-to-train (T2T) communication. Those future applications require an exchange of safety critical data between trains within one train-set based on wireless communication. Hence, the investigation of the propagation effects and the influence on the wireless communication is tremendously important. Future developments of communication standards and systems demand a detailed characterization and modeling. We investigated the propagation mechanisms based on channel sounding measurements and derived statistics for the propagation effects. Based on the environment, geometry and the propagation statistics we derive channel models for T2T communication. To cope with the movement of the trains, the changing environment and resulting temporal correlation effects we present a geometry-based stochastic channel model (GSCM) for T2T communication in open field environment.

Unmanned Aerial Vehicles (UAVs) have been widely used in military and civilian fields in the recent years, being many of their applications dependent on some strategy for sensing the environment. With full Joint Communication And Sensing (JCAS) support, increased bandwidth and higher frequency bands expected for sixth generation (6G) communication systems, a new horizon on the usage of cellular radio frequency (RF) signals for joint air-to-ground (A2G) communications and precise environment sensing is open. In this short paper, the basics of a Deep Learning (DL)-based approach for environment sensing from an UAV by using RF signals from terrestrial cellular deployments is presented. Preliminary results prove that the achieved accuracy of the location of scatterers on the environment is currently around 1 m. The proposed approach constitutes a totally autonomous JCAS solution for environment sensing whose accuracy could be even further improved by learning from previously captured data.

With the development of fifth generation (5G) mobile communication, unmanned vehicles have become more and more popular, with unmanned aerial vehicles (UAVs) and unmanned surface vehicles (USVs) being the most common ones. Collaborative operation between multiple kinds of unmanned vehicles is the trend for the future development and direct reliable communications between autonomous vehicles are mission-critical in some applications such as communication relaying and heterogeneous ad-hoc networks. This paper presents a measurement campaign for the channel between a UAV and a USV by the seaside. The UAV hovers at an altitude of 50 meters over the harbor, and the USV sails out from the breakwater with a total track length of around 3.1 km. Analyses are made on both large-scale and small-scale channel characteristics, including path loss, shadow fading, and multipath fading. The obtained results are of utmost relevance for the development of communication systems between UAVs and USVs.

Next-generation mobile communication systems employ mmWave frequency bands with high bandwidths to enable high data rate transmissions. Further, the importance of high mobility scenarios, such as vehicular communication or high-speed train scenarios, is steadily increasing. To learn how wave propagation and scattering effects change from classical sub 6 GHz to mmWave frequencies, measurements in both bands have to be conducted. We perform wireless channel measurements at 2.55 GHz and 25.5 GHz center frequency at high mobility. To ensure a fair comparison between these two frequency bands, we perform repeatable measurements in a controlled environment. Our measurement methodology enables measurements at the same transmitter and receiver positions and velocities, but at different center frequencies. We compare measured wireless channels at the two employed frequency bands in terms of the delay-Doppler function.

The risk of mid-air collisions between flying drones has to be minimized to the greatest possible extent as it endangers people in the air and on the ground especially when being integrated into dense urban airspace. For a safe and efficient operation they will need to exchange information in a robust and reliable manner and one essential part will be direct D2D communications. Especially, for dense drone scenarios in urban environments a communication system must cope with the specific underlying channel propagation conditions. In order to characterize the propagation effects between two moving drones in urban environments, we performed a channel measurement campaign and presented an approach to localize the origin of the measured multipath components for a three-dimensional layout. In this work, we apply it on our measured scenarios in three different environments in order to identify the MPCs by assigning them to real-world objects and describe first characteristics.

The emerging technology terahertz (THz) communication is envisioned to provide high-data-rate links. For the design of THz communication system, an accurate channel model is unavoidable. As a typical representative of deterministic models, ray-tracing (RT) method based on optical theory is relevant to the physical properties of THz waves. In this study, with the consideration of real-world use, two cases are made for vehicle-to-infrastructure (V2I) and drone communications. These two cases represent two ends of THz mobile communications from terrestrial to aerial one. The V2I channel is analyzed with the aid of RT. The Doppler effect caused by moving vehicles will be a great challenge for system design. As for the drone communications, the channel model should consider the three-dimensional characteristics, including scenario, velocity, trajectory, antenna pattern, etc. The provided brief survey on the two most relevant scenarios for smart mobility will be fundamental for the THz channel modeling.

The tunnel environment is a semi-enclosed space, the electromagnetic wave propagation characteristics are very different from the typical outdoor and indoor environments. Propagation model of electromagnetic waves in tunnels plays an important role in designing advanced wireless communication systems. In this paper, we firstly establish narrowband channel model for the tunnel in Line-of-sight (LoS) and obstructed line-of-sight (OLoS) scenarios, such as the path loss model, small-scale fading model. Then, we analyze the power delay profile (PDP) and root-mean-square (RMS) delay spread in the tunnel. Results show that the PDP can be well modeled by a single exponential decay with a statistically distributed decay-time constant. In addition, it is shown that the generalized extreme value (GEV) distribution has better fit for the cumulative distribution function (CDF) of RMS delay spread than Lognormal distribution in LoS scenarios. In general, RMS delay spreads in LoS scenarios is smaller than OLoS scenarios.

In this work the antenna propagation has been characterized for a 5G Wireless Train Backbone (WLTB). For this purpose, a train model has been generated and ray tracing simulations have been performed with antennas installed on the roof of the train. In order to obtain the most optimal antenna locations, the position of the antennas has been modified in vertical and horizontal directions. Tunnels have also been simulated, changing their material properties to study their effect on the signal propagation. Obtained results have allowed to identify potential locations for the antennas of the WLTB

Facing the current shortage of radio frequency spectrum resources, visible light communications (VLC) technology has been proposed to be a candidate technology in the sixth generation (6G), especially in the application of Intelligent Transportation Systems (ITS). And the propagation characteristics of VLC channel are critical for VLC system design and optimization. Furthermore, the impact of weather conditions on VLC channel cannot be ignored considering the vehicular VLC in ITS. In this paper, we experimentally investigate the impact of different weather types including fog and relative humidity (RH) on VLC in a laboratory atmospheric chamber. To simulate adverse weather conditions, we change the levels of fog density and water vapor introduced into the chamber, respectively. Then we measure the power attenuation and the bit error rate (BER) performance of VLC system under fog and RH conditions. We find that the VLC system will exhibit worse BER performance in the fog impaired channel than RH conditions. Besides, the results show that the bit errors will not happen until the attenuation reaches the threshold, i.e. attenuated by about 60% for both fog and RH conditions in our experiments. After that, the BER will deteriorate badly even up to 20%.

We propose a probabilistic connectivity model suitable for imitating link connectivity in large mobile ad hoc networks. The model is based on a two state Markov chain and captures the vital aspects that successive connectivity states exhibits dependence, and that link connectivity is a function of distance between transmitter and receiver. The maximum likelihood estimator is used to estimate parameters from measurement data. The model is found to outperform the common fixed range connectivity model.

This manuscript presents a numerical design of two-dimensional switching matrices with triangular lattice of an arbitrary number of beams, improving the overlap between beams in two-dimensional multiple beam coverage. The designs for 2x2-way and 3x3-way matrices are given as examples.

Recent and ongoing researches regarding the developments of fixed beam and reconfigurable circularly polarized (CP) reflectarrays at the state key laboratory of millimeter waves of Southeast University are reported. The CP reflectarrays are designed based on the magneto-electric (ME) dipole or patch elements, realizing wide bandwidth, high efficiency and/or low cost. Three designs will be introduced and explained: a wideband design of CP reflectarray using asymmetric dual-polarized ME-dipole structure, a low-cost reconfigurable CP reflectarray based on pin-shorted patch elements and a wideband high-efficiency reconfigurable CP ME-dipole reflectarray. In particular, the design considerations and preliminary results of the reconfigurable ME-dipole CP reflectarray element will be revealed.

In this paper, we propose a geodesic generalized Luneburg lens operating in the 60-GHz band (57-67 GHz), designed with the goal to improve the crossover level between beams with respect to previously reported fully metallic Luneburg lenses, while providing highly directive beams and wide scanning coverage. We have combined the use of a generalized Luneburg lens and the design of a compact feeding type based on ridge waveguide in order to achieve an optimum crossover level between beams keeping in mind manufacturing simplicity. The numerical evaluation of the final integrated lens design including 21 ridge waveguide feeding ports shows a S11 parameter below -13.6 dB over the frequency band of interest, a scanning range of +/-52°, a realized gain higher than 19 dBi over the whole operating bandwidth, and a crossover level value between -3.5 dB and -4.2 dB from the lowest to the highest frequency of operation.

In this paper, we present a Fabry-Perot (FP) antenna with full azimuthal beam-switching operating in the Ka-band. The system is composed of two stacked cylindrical layers. The bottom layer contains a Reflecting Luneburg Lens (RLL), which generates a plane wave and transmit it to the top part. Then, we place a Fabry-Perot cavity in the top layer that radiates the excited plane wave through a partially reflective surface (PRS) and produces a directive beam. Both the RLL and the FP cavity are azimuthally symmetric and allow one to generate identical pencil beams for any azimuthal direction. Moreover, it is possible to scan in elevation by varying the height of the FP cavity, which provides 2D beam-steering performance. The double-layer approach guarantees the compactness of the device, whereas the full-metal implementation minimizes the propagation losses. Our proposed antenna is well-suited for spatial applications, particularly for communication systems in SmallSats and CubeSats.

In this paper, the design of a continuous parallel-plate lens in multilayer PCB technology is presented. The beamformer consists of a continuously shaped lens doublet made from a stack of substrate layers and an integrated SIW feed system. Asymptotic techniques are used to optimize the lens and feed geometries. The proposed concept is validated by full-wave simulations of a lens design operating in the K-band (17.3-20.2 GHz). The final structure is matched to free-space using a linear flare and provides a total of nine beams over a +/-60° sector with low scan losses in the order of 2 dB.

This paper introduces a fast single-cut near-field to far-field transformation method using amplitude-only data. By measuring the antenna near-field amplitude on two concentric rings, the complex far-field for the corresponding ring plane can be retrieved. This avoids the full spherical scanning of traditional near-field measurements if one is interested in only a few radiation pattern cuts. In addition, the phase retrieval algorithm benefits from the reduced dimensionality of the problem. Because the number of unknowns have been reduced to a single ring, the performance is improved with respect to standard full spherical phaseless approaches. The proposed single-cut phaseless technique is tested using simulated and measured data, showing its potential for fast and more reliable amplitude-only measurements.

For large-scale inverse source problems with millions of unknowns after discretization, iterative linear systems of equations solvers are the method of choice for the solution of the resulting normal linear systems of equations. In order to reduce the related computational workload, a localized and a global preconditioning technique are presented, which speed up the iterative solution process especially for very large and complex inverse source problems. The performance of the preconditioning methods is demonstrated based on synthetic and realistic measurement data.

This work presents a Near-Field (NF) phaseless measurement system for probe-fed broadband antennas based on a flexible freehand acquisition system. The measurement probe is moved by hand in front of the Antenna Under Test (AUT), being its position provided by a sub-millimeter accuracy optical tracking system. Phase retrieval is done by means of an indirect holography technique capable of retrieving the phase of the field radiated by the AUT at each acquisition point coherently for all the frequency band. The Sources Reconstruction Method (SRM) is applied next in order to compute the aperture currents and radiated fields from the nonregular acquisition grid. Time-gating and spatial filtering techniques are employed to minimize the effect of the environment and feeding-probe, respectively, in the computed radiation pattern. The proposed system and techniques are validated by means of measurements of a broadband probe-fed antenna for WiGig applications working from 57 to 66 GHz.

The automotive industry often desires to evaluate installed automotive antennas under variable boundary conditions. This requires a combined approach to test and qualify vehicular antennas; however, facilities deploying variable boundary conditions for measurements are challenging to devise. Alternatively, numerical simulations can be used to perform such investigations; nevertheless, it is essential to verify such simulations through measurements. In the VISTA facility of Technische Universitaet Ilmenau, a new approach to providing variable boundary conditions for antenna measurements is realized to evaluate the impact of different boundary conditions and bridge the gap between numerical simulations and measurements. It consists of a modular and mechanically robust plastic frame carrying a customizable fabric substituting a ground plane. This paper presents and discusses the initial antenna measurement results performed over the conducting fabric. The convincingly good correlation of more than 74% between the measured data and numerical simulations shows the validity of the proposed method.

The experimental validation of a near to far-field transformation (NTFFT) with planar spiral scan for flat antennas under test (AUTs) is provided in this work. Such a technique has been developed by properly exploiting the unified theory of spiral scans for non-volumetric antennas when these AUTs are assumed as enclosed in a disk with diameter equal to their maximum dimension. Moreover, it uses an efficient two-dimensional optimal sampling interpolation algorithm to reconstruct the near-field data needed by the classical plane-rectangular NTFFT from those gathered along the spiral. Since the smaller the area of the modeling surface, the lower the number of near-field data and spiral turns, a further time saving is accomplished as compared to the non-redundant planar spiral NTFFTs using the modelings for quasi-planar AUTs, which instead involve a residual volumetric redundancy in such a case. The reported experimental results assess the practical feasibility of the developed technique.

Full probe compensation techniques for spherical near field antenna measurements have recently been proposed and validated with success. Such techniques allow the use of antennas with more than a decade of bandwidth as near field probes so that multi-service/frequency measurements can be performed dramatically reducing the number of probes and hence decreasing the downtime between measurements. By using dual-polarized probes the measurement efficiency can be further improved since two orthogonal field components are measured simultaneously. The possible differences between the pattern radiated by the two ports of the probe should sometimes be considered to maintain the overall measurement accuracy. A full PC technique accounting for generic dual-polarized probes was validated in a previous publication considering a wideband dual-polarized probe in the 0.4-6GHz frequency band. In this paper the validation is expanded to the 6-16GHz band considering as probe an antenna of the same family of the previous one.

This paper aims to introduce a phaseless near-field- far-field (NF-FF) transformation with planar wide-mesh scanning (PWMS) and to give a numerical validation of the technique. The here considered NF-FF transformation, based on a non- redundant sampling representation of the electromagnetic field developed by modeling the antenna under test (AUT) with a double bowl, allows to achieve a remarkable reduction (about 90%) of needed NF samples, as compared to standard λ/4 sampling. The reliability and stability of the phase retrieval problem is improved exploiting a proper representation of the unknowns and the a priori information on the AUT. Numerical results, assessing the proposed characterization technique, are shown.

Spline-based motion sequences, in contrast to canonical path definitions such as circular or linear paths, represent the optimal mode of operation for robot-based measurement setups. By specifying not a trajectory but a set of required sampling points, the robot controller is granted additional degrees of freedom to optimize the path speed or the smoothness of motion. A comparison of identical spherical near-field measurements based on canonically defined circular trajectories or based on splines yields that the latter enables to increase the average trajectory speed and, thus, to reduce the measurement time by up to 16%. Since one of the spline-based motion trajectories is derived from an irregular sampling grid, a higher-order pointwise probe correction (PPC) is used for all measurements to ensure comparability. It is demonstrated that the averaged equivalent error signal in the far-field radiation pattern is below -54 dB compared to the canonically defined reference.

During the last few years more and more electrical devices are being integrated into automotive vehicles. For this reason, an assessment of the Specific Absorption Rate (SAR) for a person placed inside a vehicle is crucial to comply with human safety regulations. SAR values depend in general on the automotive environment specifically on vehicle models and device design. A method for the preliminary assessment of SAR, that could be used in the design phase of devices by resorting to the link between measurement and simulation, is presented. It allows to reduce design time and cost. The proposed technique consists of a single measurement of a prototype, then the measured device is modeled as a NF source that is imported in CEM tools for SAR calculation. In this paper the SAR assessment is demonstrated on a roof-mounted antenna system designed by Calearo and integrated in a portion of a car model.

Increasing demand for antenna measurements has naturally increased the requirement for these measurements to be performed faster. The theory behind spherical near-field antenna measurements places a certain boundary to the number of samples needed for a complete measurement which, subsequently, sets the minimum measurement time, given a specific mechanical scanner speed. Some papers have appeared in the literature addressing this problem, but most of them assume a priori information about the antenna, in addition to the radius of its minimum sphere. The new and unique method presented in this paper may facilitate an almost 50% reduction of the measurement time in spherical near- field antenna measurements by employing the derivative of the received signal with respect to the azimuthal angle. Since it does not assume anything beyond the minimum radius that encloses the antenna under test, it can be applied universally.

This paper presents a novel dispersion hybrid implicit explicit single-field finite-difference time-domain (HIE-SF-FDTD) method which can be effectively used to simulate the graphene-based absorber. The stability condition of the proposed method is relaxed from the spatial mesh sizes along one direction which makes it a robust tool to simulate structures having fine details in one Cartesian direction such as thin graphene sheet. By applying the Crank-Nicolson (CN) scheme only to the electric field and a new time-splitting scheme to the graphene current density, the proposed algorithm is developed. In this method, not alike most of the FDTD algorithms in which both electric and magnetic fields are updated, only the electric field needs to be solved in each iteration. Thanks to the few and simple updating equations of the proposed algorithm, higher computational efficiency in terms of runtime is achieved.

In this paper, focusing on the frequency domain, we write the constitutive relation and the Helmholtz equation for linear, dispersive, and inhomogeneous time-varying media. Next, by assuming spatial homogeneity, we simplify the equations and explain how to calculate dispersion curves (the angular frequency with respect to the wave vector) for propagating waves. Furthermore, we show that under the simplifying assumption of instantaneous response, the developed general approach provides the same dispersion curves as reported earlier for the dispersionless model of time-varying dielectric media. We believe that this study is important for investigations of wave phenomena in time-varying media, properly taking into account inevitable frequency dispersion of materials.

This paper presents and compares two methods for modeling spatially dispersive metasurfaces as zero thickness sheets. In the first method, the standard Generalized Sheet Transition Conditions (GSTCs) are expanded to account for multipolar surface current densities. The extra terms in the current expansion allow for additional surface susceptibilities to be included which relate the multipolar components to the average fields and their spatial derivatives. The second method accounts for spatial dispersion by expressing the dipolar surface susceptibilities as complex rational polynomial functions of the transverse wave vector. This yields a set of differential equations relating the field differences across the surface to the average fields at the surface, leading to an extended form of the standard GSTCs. The two methods are then compared, and the multipolar modeling method is shown to be a subset of the extended GSTC method for the case of a uniform surface

We present an investigation into phase and polarization singularities of electric fields radiated by a circular electric dipole array with rotational and mirroring symmetries. By numerical evaluation, we demonstrate that the z, the right-circular and the left-circular components of the electric fields carry phase singularities with the orders of 0, 1 and -1, respectively. Furthermore, the interference of the right- and left-circular components gives rise to a V-type polarization singularity with the order of 1 in the in-plane components of the electric fields. Our work reveals the phase and polarization singularities in the circular dipole array, which could inspire further fundamental and applied explorations of electromagnetic singularities in other circular EM systems like circular antenna arrays.

The anomalous refraction of an all-dielectric 3D-printed diffraction grating is experimentally demonstrated in the microwave domain. The dimensions of the binary grating are derived using the coupled wave theory and full wave simulations. A maximum diffraction efficiency of 89% is obtained for a TE polarized incident plane wave impinging the grating at 18 GHz with a 50° elevation angle. This efficiency remains above 50% over a 35° angular bandwidth around 50° in the frequency band 17-20 GHz. Outside this angular range, the device is electromagnetically transparent. A prototype is fabricated with ABS thermoplastic using a fused-deposition modelling manufacturing technique. The structure is experimentally characterized using a near-field bi-static test bench, and the refractive behaviour is demonstrated.

This paper describes the generation of sum and difference radiation beams with a 2-bit polarization-dependent (PD) metasurface. A single-layer and cross-shaped dipole unit cell is proposed to implement the PD metasurface. By appropriately optimizing the dimensions of the unit cell, it can offer a 2-bit reflection phase for two orthogonal polarizations independently. A horn antenna is adopted as the feed source to illuminate the PD metasurface. Sum and difference radiation beams are achieved when the phase shifts of the PD metasurface are appropriately imposed in horizontal and vertical polarizations by mechanically rotating the PD metasurface 90 degrees. For demonstration, a circular PD metasurface is implemented at the millimeter-wave band. The simulations reveal that the PD metasurface-based scheme can offer stable sum and difference radiation beams from 24 to 28GHz, where the null depth levels at broadside direction are all below -20dB.

In principle, both scalar and tensor holographic artificial impedance surfaces (HAISs) can generate circularly-polarized waves. It is found, however, the previously-reported works on circularly-polarized holographic antennas are based on tensor impedance surfaces. This paper studies the generations of circularly-polarized waves by using scalar and tensor HAISs, and compare their performance in terms of design complexity, impedance bandwidth, 3dB axial ratio bandwidth, realized gains, etc. The mechanisms of producing circularly-polarized waves using scalar and tensor HAISs are first formulated and presented. Two right-hand circularly-polarized holographic antennas are then implemented with the scalar and tensor HAISs, respectively, and simulated. The simulations conclude that the tensor HAIS indeed outperforms the scalar HAIS in the generation of circularly-polarized waves. In particular, the peak gain of the tensor HAIS is much higher than that of the scalar HAIS. The conclusions obtained in this paper give a clear answer on designing circularly-polarized HAISs with good performance.

As the frequency of future communication and sensing devices increases, current proposed tuning technologies incorporate additional, and often prohibitive, losses when operating in the millimeter wave and terahertz bands. Piezoelectric tuning offers a promise of removing this inherit efficiency reduction with increased frequency, by removing the tuning element from the millimeter wave circuit and providing microsecond mechanical tuning of internal dimensions. A set of phase shifting surfaces on PDMS substrates have been simulated that operate between 20 GHz and 1 THz, that demonstrate how piezo-tuning maintains its low loss performance over this large range of frequencies. The constructs demonstrate >250° phase shift performance across all frequencies with average losses less than 1 dB. Simulations of devices using more standard substrates have been extracted from the proposed construct, which demonstrate the usefulness of piezoelectric tuning as the best-in-class method when considering loss performance.

Reconfigurable intelligent surfaces show huge potential to provide significant performance improvement for wireless communications. Low cost and power consumption, lightweight, and flexible deployment make them perfect for integration within the 5G mobile network infrastructure. However, the problems of multipath fading interference and radiation losses are prominent at mmWave frequencies. To enable massive connectivity and low-latency communications, one should tackle and eventually exploit the randomness of the real-life wireless propagation channels. In order to enable multi-User Equipment communication broadcasting, achieving simultaneous beamforming on multiple beams is of paramount importance. This paper provides a strategy to control the propagation channel via reconfigurable intelligent surfaces and generate multiple pencil beams for concurrent user access at mmWave frequencies. Compared to simultaneous amplitude and phase surface reconfiguration, this technique requires only phase coding to engineer multi-beamforming dynamically. The proposed technique creates an arbitrary number of beams that are stable among a wide frequency band.

In this paper, sub-wavelength passive periodic structures are used to create high isolation between the transmitter (Tx) and receiver (Rx) antennas designed at 26 GHz. The periodic electromagnetic bandgap (EBG) structures composed of square mushroom shapes are used between Tx and Rx (TRX) antennas for increasing the isolation from 22 dB to 50 dB experimentally. The results are compared in terms of simulation and measurement and a close agreement is found between them. Moreover, the results are further used to extract system performance targeting joint communication and radar sensing (JC&S) applications.

In this paper, Anteral presents a novel dual-band dual-circular polarization antenna feeding network for satellite communications. Circumplexer is the idea of Anteral for compactness of an antenna feeding network by integrating a septum in the common port of a diplexer. Therefore, the new device provides dual circular polarization with excellent axial ratio levels and very high isolation between channels simultaneously. Two different waveguide filters are utilized to provide very high isolation between two different channels while a septum in the common port is used to provide with the dual circular polarization. This kind of components is presented for the first time in the literature. The proposed design example accomplishes measured results with more than 23 dB return loss, 70 dB isolation between channels with an axial ratio better than 0.45 dB. Due to its compact design, it is especially attractive for satellite communications where size and weight are key parameters.

This paper presents some techniques to estimate beamforming coefficients in multibeam array fed reflector antennas with an imaging geometry generating a large number of beams, of interest for very high throughput satellite (VHTS) systems. A comparative study of these techniques is proposed using an antenna configuration designed to meet VHTS system requirements with full earth coverage. The impact of removing the amplitude information from the elements excitations is also considered with different scenarios. Numerical results in terms of carrier-to-interference (C/I) are reported to compare the impact of the different scenarios and techniques on the performance of the satellite antenna system over the defined coverage.

A dual-band (Tx/Rx) multiple spot beam reflector system for high throughput satellites in Ka-band is presented. The configuration is a multiple-feed-per-beam dual reflector Cassegrain antenna with a frequency selective surface (FSS) sub-reflector that separates the response between Tx and Rx frequency bands. Using this configuration, a full multiple-beam coverage employing the four-colour frequency/polarisation reuse scheme can be produced using only a single main reflector. By utilising a modulated FSS sub-reflector, the performance of the antenna system is significantly improved compared to using a periodic element distribution on the sub-reflector.

The design of the feeding system for the focal array in OLAF (Over-Lapped Sub-Array Fed) antenna for SAR Instrument at L-Band is presented. The proposed design consists of a circular patch with a balanced excitation all of it embedded in a ground plane which is connected to the lower ground plane by some shorting pins, reducing the mutual coupling with the neighbour radiating elements of the focal array. The balanced excitation has been implemented with a 180º hybrid using the differential input port. Dual polarization is achieved by using two 180º hybrids within the same layer. The stringent requirements for the system, namely low in cross-polarization, high isolation between the two polarizations (both below the -25dB reference level) and azimuthal symmetry of the radiation pattern are fulfilled within all the working bandwidth.

A miniaturization of a CORPS-BFN (Coherently Radiating Periodic Structures - Beam Forming Network) to properly feed OLAF (Over-Lapped sub-Array Fed) antenna for SAR Instrument at L-Band is presented. The original beam forming network was based on 4-ports Gysel power combiner/divider implemented in a suspended strip-line technology, and in this work a strong miniaturization technique has been applied to fit it in the desired lattice of 230 mm, which is slightly less than a wave-length of the higher frequency of the system (1.215-1.3 GHz). The minimized version still provides low insertion and return losses, high isolation between input/output ports and the required overlapping between the different equivalent beams.

Manufacturing inaccuracies are detrimental to performance of antennas. The effects of parameter deviations are particularly noticeable for narrow- and multi-band antennas and manifests themselves through relocations of the operating frequencies or bandwidth degradation. The ability to reduce the system sensitivity to tolerances is therefore an important design consideration. Unfortunately, robust design is a challenging task, primarily because it has to be carried out at the level of full-wave electromagnetic (EM) simulation models, which generates considerable computational expenses. In this paper, we propose a novel approach to tolerance optimization of multi-band antennas. The objective is to enlarge the maximum levels of geometry parameter deviations that still ensure perfect (100-percent) fabrication yield. The presented approach involves feature-based regression surrogates as well as the trust-region framework to ensure low cost and convergence of the optimization process. Numerical validation of the method, conducted for a dual- and a triple-band microstrip antenna, corroborates its efficacy.

In this study, we developed an efficient microwave wireless power transmission (MPT) system for multiple receivers using an optimization method. The optimization algorithm finds the optimal transmission signal for transferring the desired power to multiple receivers with maximum power transfer efficiency (PTE). We designed a 5 × 5 rectangular patch array antenna and patch element antenna operating at 10 GHz as the transmitter and receiver, respectively. The operating process of the MPT system using the optimization method is analyzed. Additionally, we compared the received power of each receiver and the PTE of the optimization (OPT) technique with that of the multi-receiver time-reversal (TR) technique considering various scenarios. The OPT algorithm generates a multibeam to charge multiple receivers simultaneously. We validated that the OPT technique can deliver power to receivers precisely at desired ratios with greater PTE than that of the TR technique in an MPT system.

A broadband non-periodic mushroom antenna is designed via Bayesian optimization. By tuning the length and width of the 16 patches of a 4 × 4 metamaterial mushroom structure, the non-periodic mushroom antenna achieves a 23.95% fractional bandwidth (|S11|<-10 dB), while keeping the gain variation small at boresight direction. Bayesian optimization is particularly suitable for design and optimization with a large number of design parameters, for example, 32 design parameters in this design, since the conventional exhaustive search becomes infeasible for such a large search space. The proposed antenna is prototyped and measured, with good agreement between the simulation and measurement achieved. The proposed antenna is able to operate in the widely deployed n78 band of 5G New Radio.

This paper proposes an algorithm for the automated design of metasurface antennas. From the objective radiation field and the feeding structure, it allows to obtain a surface current distribution that leads to a passive and lossless impedance profile on the radiating aperture. The surface is modelled by a scalar impedance boundary condition and the electromagnetic problem is formulated as an electric field integral equation. The approach is entirely numerical, based on the gradient descent optimization of a scalar objective function that incorporates passivity and far field requirements. This procedure was applied to the design of an electrically large circular metasurface antenna at 32 GHz, obtaining a lossless impedance profile with satisfactory radiation properties.

We derive a simple and efficient method for designing wave--shaping materials composed of dipole scatterers. We apply our theory to design aperiodic metasurfaces that re-structure the radiation from a dipole emitter in many ways, including increasing the efficiency of a small emitter and re--shaping the far--field radiation pattern. Our proposed technique is relevant to designing metamaterials for a wide class of applications and has the key benefit of including all interactions within the system of scatterers.

A dynamically reconfigurable wave-chaotic metasurface antenna is presented to perform computational polarimetric microwave imaging. The metasurface is synthesized using sparsely distributed sub-wavelength super-cells, each consisting of two orthogonally separated complementary electric inductive-capacitive (cELC) unit-cells. These super-cells radiate selectively (under PIN diode control) in both vertical and horizontal polarizations, ensuring that the synthesized wave-chaotic modes are polarimetric in nature. Leveraging the dynamically modulated waveform diversity of the incoherent wave-chaotic radiations from the metasurface antenna, polarimetric imaging is computed in the near-field region at K-band frequencies and the polarimetric responses of specific targets are retrieved.

In this work, we propose a phase-gradient metasurface reflector for millimeter wave (mmWave) and the fifth generation (5G) mobile network applications. The proposed metasurface is composed of periodically arranged metallic patches loaded with square rings, backed by a ground plane. Numerical simulations and experiments are conducted to validate the designed metasurface reflector, and results show that the RCS and beamwidth are considerably affected by the overall size of the reflector, and in situations when the receiver is in non-line-of-sight (NLOS) with the transmitter, the metasurface reflector can improve the received signal strength by more than 10 dB.

This work presents a state-of-the-art development of an ultrawide absorber for wearable smart electronic textile applications. The design is based on a novel cell geometry that is previously developed and applied for RF energy harvesting applications. Different textile types were considered in this study, namely, Felt, Denim and Polyester and the achieved -10 dB reflective fractional bandwidths are about 42.828%, 43.65%, and 42.834% respectively. A comparison with traditional counterparts (FR-4 and Rogers dielectrics) shows that the bandwidth exhibited by textile materials is greatly wider. The bending effect of the textile materials is considered in this study and found that the -10 dB bandwidth is inversely proportional with the decrease in the surface curvature of the material. Compared to the currently developed absorbers and similar structures reported in the literature show that the current design is more compact, lighter, and more efficient in terms of the absorptivity.

An original numerical approach for investigation of a circular waveguide, containing a co-axially positioned ferrite cylinder of azimuthal magnetization and a dielectric toroid and that propagates normal-TE01mode, is developed. It utilizes certain positive purely imaginary roots in the independent variable of the characteristic equation of the structure, derived in terms of the-complex Kummer confluent hypergeometric and real zeroth and first order Bessel and Neumann functions and specific real numbers (L3_numbers). The latter are connected with other roots of the equation mentioned and have been defined and discussed by the authors in earlier studies. Tables of the roots in question and of the L3_numbers for selected values of parameters of the-configuration are given. Using them the lower and upper cut-off frequencies which specify the boundaries of the area of phase shifter operation of the transmission line are determined. The-discussion is confined to the case of a-thick ferrite and a-thin dielectric layers.

Microfluidic technology has been improving continuously in recent years due to constant research and development in the area motivated by the high efficiency and low cost features. Most of these devices are controlled or triggered using on board power supply, wired connections or specific chemical reactions. In this paper, we propose the wireless electromagnetic triggering for mixing in microfluidic chips. The preliminary results obtained from simulations in COMSOL Multiphysics show that interaction of microwaves with metallic microparticles can generate enough heat to switch thermosensitive valves in a microfluidic chip for enabling microfluidic mixing.

This work is dedicated to the electromagnetic eigenvalue problem for twin dielectric nanorods made of the gain material and coated with graphene monolayer covers. This problem is adapted to the modeling of the optical modes at the threshold of lasing, where they have real-valued frequencies. Each eigenvalue is a pair of numbers: frequency and threshold gain index. Due to two-fold symmetry, twin-rod open cavity possesses modes of four different symmetry classes. We derive separate determinantal equations for each class, using the separation of variables in the local coordinates, the addition theorems for the cylindrical functions, the Kubo formalism for the graphene conductivity, and the resistive boundary conditions on the rod contours. Sample numerical results demonstrate how the plasmon supermodes of graphene-covered twin rods form the quartets made of two doublets with close frequencies. Our analysis will be useful in the design of novel plasmonic nanolasers with graphene resonance elements.

Absorptivity control is a very desired feature in many RF applications as it allows enhancing EM properties such as antenna radiation patterns and reducing radar cross section. In this paper, two Salisbury-inspired structures with absorption level of 20% and 50% in X-band frequencies (8 - 12 GHz) are presented. Both structures are fabricated by electron beam evaporation technique with Nickel Chrome as material for the resistive coating on a PEKK dielectric substrate, which is manufactured by thermal compressing. The characterization in non-anechoic environment confirms the results obtained by numerical computations. For both vertical and horizontal polarizations, quasi-perfect agreement over the frequency band of interest is found with a maximal variation of the absorptivity less than 5% between the center frequency at 10 GHz and the edges frequencies at 8 GHz and 12 GHz. The absorption behavior of the two structures was also evaluated under oblique incidence.

A Dual-band and dual linear to dual circular polarization single-layer transformer Frequency Selective Surface (FSS) in reflection mode for satellite communications is presented. The unit cell proposed provides a low-profile antenna implementation and low-cost solution, achieving an axial ratio below 1dB in a frequency range from 17.7-20.9GHz (16%) at K band and 28.6-30.1GHz (5%) at Ka band. The obtained bandwidth fulfils the ITU frequency band for most of the global region. Besides, the dual-circular polarization is obtained be using a two linear polarization feed with two ports. This reduces feed chain complexity, weight and cost.

In this paper, we introduce a design methodology for passive magnetic metasurfaces with controlled response excited by an active RF coil placed in its near-field region. Starting from conceiving the geometrical parameters of the radiating system, we first create the mask reporting the desired magnetic field distribution to be achieved at a certain plane. After that, the currents, in amplitude and phase, producing the desired field distribution, are evaluated. This step is carried out through an optimization algorithm, based on a magneto-static hypothesis. Then, we determine the capacitive loads required to achieve such behavior, exploiting a single full-wave simulation. Finally, numerical simulations of the overall designed radiating system are performed to validate the obtained results. The possibility to rapidly design and configure a passive metasurface, able to show the desired magnetic field distribution, can be a valuable tool in different applications, like magnetic resonance imaging and wireless power transfer.

A block of digital anisotropic low-visible puzzle-type coating, which also consists of puzzle-type antiphase modules, are offered to improve the diffusion of scattering. The scattering characteristics of this block are compared with the characteristics of a block with square-shaped modules. Both 2-bit meta-coatings (MCs) are made from meta-particles of a dumbbell-shaped form and constructed on the base of block matrices of coding. Simulation shows that the diffraction lobes of the bistatic RCS diagrams of the puzzle-like MC fill the front half-space more uniformly in the sector of meridianal scattering angle of 30°...70°, compared to MC made of square modules. Monostatic RCSs for co-polarizations under normal irradiation are reduced by no less than 10 dB in X-, Ku-bands.

This paper presents a theoretical study that establishes the performance limits for a multi-layer transmitarray unit cell. This is the first study to be applicable to unit cells in which the conducting resonators, on the different layers, are shaped differently. The study enables one to account for the effects of dynamically reconfiguring the resonators on certain layers (e.g. through shape change). Specifically, the paper quantifies the range of phase shift values, available from the unit cell, for a given amplitude of S21. The first step in the study was to derive theoretical calculations. The theoretical calculations predict that, for an S21 amplitude of -1 dB, unit cells having three conducting layers can provide a phase shifting range of 360°. It is achieved when the geometries of the resonators on the different layers are varied independently. Then the theoretical calculations have been validated through computer simulation

We use the exact form of the Green's function for a grounded dielectric slab with a superstrate to derive approximate analytical expressions for the propagation constant of the fundamental surface wave. The result is then used to obtain a closed-form expression for the scan blindness condition in an infinite phased array of printed dipoles with a superstrate. The analytical criterion of scan blindness is validated with a full-wave simulation of Maxwell's equations.

A compact frequency reconfigurable antenna is proposed in this paper for 5G applications. Conventional circular patch antenna was modified using two pairs of open ended horizontal and vertical stubs. Stubs cause the improvement in impedance matching along with increased effective area of the radiator. Afterwards, two PIN diodes were inserted in the vertical pair of stubs to achieve frequency reconfigurability between 24.8 GHz and 28 GHz band spectrum. The antenna was designed and simulated using Higher Frequency Structure Simulator (HFSS) using appropriate boundary conditions with RLC equivalent model of Pin diodes.

In this paper, an equivalent circuit model of an unbalanced fed tightly coupled dipole array (TCDA) is proposed. Unbalanced excitation can be decomposed by even and odd modes excitation. Antenna input impedances of each mode are expressed and their relation to that of unbalanced mode is determined. Herein, determining an even mode circuit is focused on to construct an equivalent circuit of unbalanced mode. Additionally, the unbalanced fed TCDA with shorting vias is proposed, and its bandwidth is compared with that of the balanced fed TCDA.

A new design approach for linear polarization scalar metasurface antennas is presented. The method consists in building up the required scalar surface impedance Zs using the already known phase-matching technique, whereas the novelty resides in achieving linear polarization as a sum of two reverse circular ones. The procedure leads to better antenna performances in terms of sidelobe levels and beams symmetry, using a smoother gradient metasurface comparing it to previous solutions. This approach is suitable for both broadside and tilted beams antennas.

Helical antennas placed between two infinite metallic parallel plates are investigated. This study is concerned with the resonant electrical length of helical antennas. The first resonance appears as the helical antenna is transiting the frequency gap between its well-known normal and axial modes of operation. A parametric study is conducted to calculate the resonant electrical length as a function of the helical parameters, namely the radius and pitch of the helix. The results are validated by comparing the solutions of two independent problems, one is driven with a source and the other is an eigenvalue problem with periodic boundary conditions. The presented results are useful in the design of gap waveguides where the periodic media are made of helical wires.

A new tool for analysing antenna radiation patterns is proposed in this article. This tool consists in applying a spherical wavelet transform to the radiation which is assumed to be known on a regular spherical-coordinates grid. This is an alternative solution to usual plane-waves or spherical harmonics expansions. The interest of using wavelets is to obtain a better analysis in terms of localization in position and/or direction. The direct link between spherical wavelets and spherical harmonics is also highlighted. The properties of this tool are illustrated by means of numerical experiments performed on two typical antennas, a canonical aperture and a pyramidal horn.

This paper presents the design of an Ultra Wideband (UWB) antenna mainly dedicated for Ground Penetrating Radar (GPR) application in the frequency band between 150 MHz up to 550 MHz. With its compact electrical size in the low band, the initial double exponentially tapered slot antenna (DETSA) exhibits a low directivity and Front-to-Back ratio. With the guidance of the Characteristic Modes Analysis (CMA), it was possible to identify the best loading position as well as the optimized load values to enhance these antennas properties. The optimized loaded DETSA demonstrated a significant directivity enhancement and a Front-to-Back ratio that exceeds 4dB inside the band.

A high-gain, Yagi-Uda like, omni-directional antenna is presented. The antenna is composed of a centered dipole, fed from downside and circular directors. No reflector is involved. The directivities of the antenna are 2.1, 2.6, 4.9, 5.5 and 6.0 dBi for the dipole alone and for the dipole with 1, 2, 3 and 4 directors respectively. The vertical height is less than half wavelength.

A Conventional Strongly Coupled Magnetic Resonance (CSCMR) system provides higher Power transfer efficiency and less sensitivity to misalignment compared to a traditional Strongly Coupled Magnetic Resonance (SCMR) system.This paper proposes, for the first time, a physical investigation of the SCMR and CSCMR systems based on the Theory Characteristic Modes.

Planar antennas have been widely used in UHF RFID systems. Placement insensitivity and thin form factor are essential qualities of planar RFID tag antennas. As the antennas become thinner, most of the energy is stored within the region between the antenna and the ground plane resulting in the degradation of bandwidth and radiation characteristics. Serrations can be used as edge treatment to improve the bandwidth of planar antennas. The analysis of edge-treated planar antennas using characteristic mode theory is presented in this article. The effect on serrations on the resonant frequencies and radiation characteristics of resonant characteristic modes of a rectangular plate is presented and guidelines are presented for improving the bandwidth of planar antennas.

In this paper, an ultrawideband microstrip to narrow wall waveguide transition operating at the E-Band is presented. The transition is based on exciting a microstrip folded dipole which radiates into the waveguide. The back-to-back transition provides a fractional bandwidth (FBW) of 20% and measured insertion losses (IL) ranging from 0.65dB to 1.35dB in the whole band of operation.

We present a new integrated wideband dual-polarized magneto-electric dipole antenna array merging the concepts of tight coupled elements and gap-waveguide feeding technology. Our proposal consists of a 4x4 directly fed unit elements, with passive-behaving elements at the borders. The radiating element was chosen as a modified bowtie antenna, with slight transition for good impedance matching control. The antenna is fed by an air filled cavity backed layer, placed directly above two layers of a modified inverted microstrip gap waveguide. The complete device can be easily manufactured by low-cost printed circuit board (PCB) fabrication processes. Numerical results demonstrate an impedance bandwidth of 68.6%(16.1 GHz-32.9 GHz) for the vertical polarization and 73.3%(15.2 GHz-32.8 GHz) for horizontal polarization, considering a VSWR (voltage standing wave ratio)<2.

In this paper, a generalized far-field pattern synthesis technique is presented. This technique is used to design an electrically small directive parasitic antenna array with end-fire radiation characteristic, having an electrical size ka=0.9 and driven with a single feeding port. The CST-MWS simulated super-directivity condition shows 10.1 dBi directivity for a three-element parasitic array with a 28.6% radiation efficiency, resulting in a 4.7 dBi gain. For gain and radiation efficiency enhancement, the way to achieve a super-gain condition is demonstrated, with CST-MWS simulated gain showing 6.6 dBi and 99.7% radiation efficiency for a three element parasitic array.

A novel ultrawideband tightly coupled dipole array (TCDA) unit cell is presented. The proposed design uses spiral based coupling elements between the tips of the dipoles unlike capacitive coupling employed frequently in the design of TCDA's. The proposed unit cell delivers 1:4 bandwidth under -10 dB active S-parameter in the infinite array environment, similar to those with known design approaches. However, this proposed unit cell is capable of better control of resonance condition by employing inductive capacitive hybrid coupling between tips of the dipoles compared to the traditional approach of single discrete capacitive coupling. The proposed TCDA unit cell is optimized such that it provides -10 dB active S-parameter in the 0.5-2.0 GHz frequency band. Finite array characteristics and scanning abilities are investigated.

This paper summarizes the initial phase of the study of the antenna element for a future SMOS radiometer mission. The paper shows the antenna main requirements, the potential antenna candidates and the main design constraints that drive the initial selection of the antenna candidate. A major difference with respect to the antenna element of the current SMOS mission is that the new element should respect the alias free spacing. An overview of the main preliminary antenna performances of the selected candidate is shown.

A compact low-cost series end-fed 1 x 10 array antenna on polypropylene (PP) for imaging applications in the 24.04 - 24.25GHz band is presented. The envisioned use is in a wearable radar system for collision avoidance to aid visually impaired people. The eco-friendly PP substrate is electromagnetically characterized at 24.15GHz for the first time. A modified Dolph-Chebyshev (DC) distribution is optimized in simulation to achieve an improved performance in terms of beam width, Side-lobe level (SLL) and Gain. A prototype of the PP based array antenna is fabricated and tested. The overall size of the antenna is 98.68 x 14.4 x 0.52 mm3. Consistent agreement is achieved between simulation and measurement results. Comparison with literature shows that the proposed array antenna overcomes the state of the art on 24GHz antennas for wearable radar applications.

This paper presents a new stepped-height ridge structure to reduce the guided wavelength of a conventional ridge gap waveguide. Compared to other technology, the stepped-height ridge gap waveguide avoids dielectric loss and reduces the cost of manufacture. The simulation results prove that the guided wavelength could be decreased significantly by adjusting the step numbers and step depth. Based on this structure, a dual circularly polarized inclined slot pair is investigated and simulated. The slot pair is located on the top plate of the ridge gap waveguide and is fed by a traveling wave. The simulation results show that the inclined slot pair could generate a good dual circular polarization with the axial ratio below 3 dB over 76-81 GHz. The discrete models of the inclined slot pair are also shown in this paper.

A dual-polarization array antenna based on over-moded parallel plate gap waveguide is presented in this paper. The antenna has only one metal waveguide layer that leads to simplification of manufacturing process. The antenna sub-array has four patches that are excited by a parallel plate gap waveguide through a cross slot. Two reflectors are utilized to feed the parallel plate gap waveguides in two directions. The simulated results show that the antenna bandwidth is 8.8% while its maximum gain is 25.5 dBi and its efficiency is about 85%.

A new sub-millimeter-wave Validation Standard ((sub)mm-VAST) antenna for use covering frequencies from 89 to 1200 GHz is being developed as a collaborative effort between EOSOL, Radiometer Physics GmbH (RPG), Space Structures GmbH (SPS) and Universidad Politecnica de Madrid (UPM) under contract from the European Space Agency. The electrical and mechanical requirements are discussed, with special attention given to the crucial measurement stability requirements. The antenna must be stable in typical measurement setups both thermally and mechanically due to gravity loads dependent on position and rotation. As well as this, it must present high gain and challenging features, such as asymmetric sidelobes, differing beamwidths and other electrical radiation qualities usually present in satellite antennas. Several antenna types are studied, after which a baseline electrical model is described and its results presented.

Two different alternatives of a dual polarization feeder for Fabry-Perot cavity antennas are discussed. They are based on a cavity baked double slot antenna fed by waveguides running in different directions, so that the double polarization is obtained. Their performance has been found to be similar in terms of return loss and radiation performance.

Photoconductive antennas are devices that provide power up to THz frequencies at a relatively low cost. However, the power radiated by each antenna is typically quite low and arrays have been proposed to increase it. In this paper we present the design of an array architecture that surpasses the state of the art as it operates efficiently for frequencies up to 1THz, without excessive complications in the manufacturing. This architecture demonstrates clean radiation patterns and high bias efficiency.

This paper presents a tilted beam antenna design working at 155 GHz. The proposed antenna is based on a Fabry Perot resonant cavity antenna concept. Using a metallic partially reflective surface the reported antenna is fed by a rectangular waveguide, and as such is designed to be compatible with the available 3D metal printing techniques. The beam tilting is achieved by grading the size of the perforations in the unit cells of the PRS. A beam tilt of 15° is shown with a gain of 18 dBi at the operating frequency. Moreover, a feed offset approach is proposed to further improve the beam tilt angle.

A 4×4 butler matrix based on ridge gap waveguide (RGW) is presented for 60 GHz applications. The proposed Butler matrix consists of four ridge gap waveguide-based couplers, a cross-over and four phase shifters .The simulation results show that return loss and isolation of the Butler matrix are better than 15 dB. Also, power-split imbalance of ±1 dB and phase error of ±7o is achieved over the bandwidth of 59-61 GHz. This wideband Butler matrix design can play a great role while designing wideband beam forming feed network, comparator network etc. for the antenna arrays at millimeter-wave frequencies.

The tendency of customized communication has inspired the fifth-generation (5G) and above technologies, characterized by multi-node and localization. Therefore, high requirements are raised of the omni-directional beamforming of base stations. An omni-directional subarray beamforming scheme is proposed, based on Butler matrix fed array. For this purpose, two array configurations are provided, using circular and cylindrical structures, and fed by multiple Butler matrices, so as to flexibly select sub arrays as excitation. Combined with practical application, the general solution of the connection form of multiple overlapping Butler matrix is derived, based on the circular symmetry. The vertical and azimuth beamforming performance of the proposed array structure is numerically calculated, and the feasibility and superiority of the proposed scheme are verified.

A novel application of the Planar Inverted-F Antenna (PIFA) is shown for operation as an element for a tightly coupled array. 3:1 impedance bandwidth is demonstrated at millimeter wave frequencies, with VSWR < 2.5 from 15-45 GHz. The proposed configuration has only a single substrate and superstrate matching layer. The array is designed for a 75-ohm feed through the ground plane. An additional matching section made through the bottom ground plane is utilized for matching to 50 ohms. Performance analysis is conducted on the unit cell using Ansys HFSS's frequency domain solver and CST Microwave Studio's time domain solver. Further demonstration is performed with a 4-by-4 finite array, where reasonable central-element match and realized gain is obtained.

Many companies are launching a lot of small satellites into the low Earth orbit in order to build the worldwide internet services. The ground stations are required to communicate simultaneously with several satellites. It is impossible for the parabolic antenna to track simultaneously several satellites. Therefore, we are newly developing a ground receiving station using the three dimensional Phased Array Antenna and the Digital Beam Forming technologies, which can simultaneously receive the signals from many satellites. We are developing the MMIC for the three dimensional phased array antenna as the student project. We will make a report on the designs of the MMIC and performances for the phased array antenna at my presentation.

We analyze a loop antenna array proximity coupled to a coplanar feed line using the method of moments. First, a novel-loop array at a uniform proximity distance (PD) from the feedline is investigated versus loop height above the ground plane. It is found that when the loop height is L0/5 (L0: wavelength), a 3 dB axial-ratio bandwidth reaches 11%, which is 3.5 times as wide as that of a conventional-loop array. Subsequently, we transform the uniform PD into multiform PD's to enhance the gain of the novel-loop array. It is revealed that the array has a gain enhancement of 1.8 dB compared with that at a uniform PD and still shows an axial ratio bandwidth of 7%.

In this paper, two innovative 4x4 Butler matrix-based antenna system designs are proposed for mmWave/5G applications which are capable of beam scanning/steering at Ka-band. By utilizing the multilayered substrate integrated waveguide (SIW) structure, the size of antenna system design is miniaturized. Beam forming can be achieved due to the application of beam forming network (BFN) based on Butler matrix. Designed beam steering antenna systems with miniaturized 4x4 Butler matrix show frequency range from 26 GHz to 38 GHz. Overall design structure sizes of two designs are 114.3 mm x 23.8 mm x2.2 mm and 112.3 mm x 18.0 mm x 3.3 mm respectively.

A holographic-inspired one-dimensional leaky wave antenna is proposed, which is capable to control independently multiple radiated beams with a single feed. Contrary to previous implementations, where multiple feeds were used for the excitation of an equal number of beams, or where a metasurface was divided into sectors, each one controlling a different beam, here we offer a reconfigurable single-source metasurface antenna designed with superposition of each individual beam modulation. The unit cell of the proposed antenna is tuned with a low-loss Schottky diode for operation at millimeter-wave frequencies. Simulated results for the novel multiple beam antenna verify the theoretical analysis, and exhibit an independent beam steering at 85 GHz.

A Fabry-Perot leaky-wave antenna with beam steering capabilities is presented.This design utilises a high impedance surface (HIS) as the first layer, a partially reflective surface (PRS) as the second layer and a plain dielectric slab as the third layer. The scanning of the antenna beam is accomplished by adjusting the operating frequencies within the 60 GHz range (58-67 GHz). This simple configuration generates a pencil beam with an S11 bandwidth (BW) of 9GHz, a scan range of 30° in the H-plane and a maximum gain of 24 dBi at 62.5 GHz.

An uniplanar compact array-HIS antenna suitable for imaging in the ISM mmWave frequency band (24.05 GHz - 24.25 GHz) is presented. Collision avoidance system to support blind people is the intended application. Different arrangements of the HIS unit cells are considered in the combination with the basic array, to improve the radiation parameters. Prototypes of both, the basic array and an optimized array-HIS are fabricated and measured in an anechoic chamber. Comparison between simulation and measurement is conducting in terms of impedance matching, bandwidth and gain. The achievements of the optimized array-HIS are compared with the state of the art antennas at 24 GHz

High-gain polarization-reconfigurable antennas in the millimeter-wave (mm-wave) band are of high importance for 5G and future wireless platforms. This paper reports an innovative mm-wave antenna that accomplishes multi-linear polarizations (LPs) with high gains. It employs a TM510-mode cavity etched with a circular slot array on its top surface as the base excitation. A two-layer copper-cladded main substrate is introduced above the base cavity to produce a high gain beam with a low cross-polarization level. Moreover, five reconfigurable LPs can be attained by rotating the main substrate at a 36˚ interval. Simulated characteristics were validated by measuring the prototyping multi-LP cavity-backed antenna. The measured overlapped -10-dB impedance bandwidth ranges from 28.58 to 28.99 GHz for the five LPs. Within this bandwidth, measured realized gains vary between 15.5 and 16.8 dBi.

This article uses a new multi-layer PCB technology to design a low-cost mm-wave circularly polarized broadband antenna array for 5G handsets that operates from 57 to 64 GHz. This band covers many 5G bands. The design strategy is explained to allow the reader to easily design a similar antenna. The antenna is fabricated and measured. Measurement results show matching better than 17 dB across the band, gain greater than 10 dBi, and axial ratio less than 3 dB. Also, the measured radiation patterns for the array show good agreement with simulations.

In this paper, a mechanically steered phase shifter with planar structure is presented for Ka-band satellite user terminals. The proposed phase shifter is composed of a power divider based on ridge gap-waveguide (RGW) and a phase-shifting section based on double-layer groove gap-waveguide (GGW) with a shared rotatable plate. The simulated results show that the phase shifter could achieve 13.6% impedance bandwidth with the reflection coefficient below -15dB. Meanwhile, the insertion losses of all output ports fluctuate around 6 ± 0.5dB and the phase differences remain stably linear over the whole operational bandwidth.

This paper presents a circular-polarized gap-waveguide-based compact monopulse array antenna for millimeter-wave tracking applications at Ka-band (29 to 31 GHz). The gap waveguide planar monopulse comparator network is integrated in a single layer with a 2 x 2 corporate-fed network combining ridge gap and groove gap waveguides. Radiating cavities consist of cubes with chamfered corners. Preliminary results show a bandwidth of 2 GHz with input reflection coefficients better than -20 dB for both ports of the antenna. In addition, the isolation between ports is greater than 50 dB. The design allows for scalability to build higher gain arrays as from the antenna presented in this communication.

A focal plane array of extended-hemispherical silicon lenses coupled to aluminum coplanar-waveguide (CPW) Kinetic Inductance Detectors (KIDs) has been designed to operate at 7.8 THz. Low-dispersive leaky-wave radiation has been used to efficiently illuminate the antireflection-coated lenses. To minimize the radiation loss from the antenna feeding lines at these high frequencies, the CPWs have been miniaturized down to the microfabrication limits and placed on a dielectric membrane. The device is currently being fabricated and its experimental characterization in terms of optical coupling and beam patterns will follow.

A V-band Vivaldi antenna design for beyond-5G base station applications operating within V-band is demonstrated. The device can be used for interfacing with radio-over-fibre links and optoelectronic components through a coplanar waveguide to slotline transition. Simulations show an end-fire radiation with a 3dB gain bandwidth ranging between 46.9-77.4 GHz combined with the reflection coefficients remaining below -10 dB for the same frequency range. A comb structure inspired by optical grating couplers is added providing an increased maximum gain of 12.6 dBi at 68.5 GHz. Measurement results validate the promising characteristics of the planar antenna.

In this letter a new switch matrix topology has been introduced for HF applications. A HF switch matrix is designed and realized by digitally on a Zynq Ultrascale FPGA core. This topology is named as Digital Switch Matrix (DSM). The DSM performs switching between 32 input ports to 32 output ports in full fan out configuration. This structure provides switching any output can be switched to any input without blocking any other output or input. Traditional switch matrixes so called analog switching matrix in this letter, consists of number of distinct RF boards for each input and output channels. These solutions are costly and have a big form factor. The proposed DSM does the same job on a single board. Therefore, it has superior advantages regarding both low cost and form factor. The measurement results of the proposed DSM are presented.

The influence of the diffraction of electromagnetic waves at a limited area in front of the glide path beacon on the behavior of the aircraft approach trajectory for landing is considered. The underlying surface at the coastal airfield is represented by a perfectly conducting half-plane. An asymptotic expansion of a rigorous solution to the problem of diffraction of a spherical wave by an ideally conducting half-plane is used. The calculated results are compared with the experimental results obtained in flight.

Measurements performed by disdrometers are often used in order to study and characterize the impact that precipitation induces into electromagnetic waves. This paper presents the 1D-Video-Disdrometer (1DVD). Thanks to the generous measuring area offered by this device, the sampling effect often associated with the disdrometers available on the market can be attenuated. It was found that the rain amount measured by the 1DVD is affected by an error smaller than 0.6% and the specific attenuation can be derived with an error not larger than 3.5%.

The 0ºC isotherm height is used in rain attenuation prediction models to calculate the rain height, as proposed in ITU-R Recommendations. In a previous study, statistical results on the variability of the 0ºC isotherm were obtained for Madrid from ten years of radiosonde measurements. Such results are compared in this paper with statistics calculated using the 0ºC isotherm height provided by ERA5. The height of the melting layer was investigated previously through the comparison of the 0ºC isotherm height, considered to be the top of the melting layer, with the height of the bottom of the melting layer derived from measurements performed with a vertical Doppler radar (MRR-2). The profiles of the velocity of falling particles provided by this radar have been used recently to calculate both the top and bottom of the melting layer. The first results are presented in this paper.

The protection and safety of vulnerable road users such as pedestrians and cyclists is essential specially in urban areas. Project CYCLOPE aims to provide technical solutions to integrate cyclists and ensure safety for pedestrians in urban areas. Automobile radar technologies are integrated in automobiles for detection of vulnerable road users to decrease accidents. However, targets such as pedestrians and cyclists can have a low radar cross section and hard to detect. Retrodirective metasurfaces can be a key solution when integrated along side targets to enhance their RCS detection. In this paper, we design a dual polarized retrodirective metasurface at a given angle of incidence. Furthermore, we demonstrate a human model and measure its RCS at 24 GHz using an automobile radar system with and without the retrodirective metasurface. The results show a gain of 15 dBm in terms of RCS detection when implementing the metasurface design.

The problem of the estimation of the directions-of-arrival (DoAs) in sub-arrayed planar arrays is addressed in this work by means of a strategy based on the Bayesian Compressive Sensing (BCS). The DoAs estimation performance for different sub-array configurations are discussed and compared, considering different noisy conditions. Preliminary numerical results are reported for single snapshot data to validate the proposed strategy.

Simple surface-wave (SW) excitation by means of a simple parallel-plate waveguide (PPW) for substrate integrated image guides (SIIGs) is proposed. As a proof of concept, a wideband, low profile and fully planar feeding network is designed. It consists of a surface-wave launcher (SWL) based on a truncated PPW with the addition of a sub-wavelength matching section. This method for SW excitation is intended to overcome the feeding limitations encountered when using SIIG based antennas or other non-radiating structures at microwave frequencies. A comparison between the performance of the proposed excitation method and structures that can be found in the literature are reported showing an improved bandwidth of more than 50% with respect to previous studies. In addition, this simple feed system has a reduced volume of more than 95% when compared with other alternatives, demonstrating its compactness. Applications include new SW driven feeds, leaky-wave antennas, sensors, or novel passive structures.

The human appearance can be interpreted as a disturbance, convenience or even necessity, for example, in technical applications with human-robot interaction and humangesture detection. This implies the need for implementing a realistic human digital twin with its positions, gestures and individual movements in ray-tracing simulations. Thus, bringing harmony between simulation and measurement owing to the more realistic assumptions within the simulation environment. In this paper, the human-digital twin combo is primarily realized based on two rationales: Firstly, a 3D human model is generated whose individual segment movement is represented by individual trajectories. Secondly, the inertial measurement units (IMUs) are placed on the human body for capturing the human motion estimation. The data fusion between different human postures and ray-tracing is achieved using a self-written script applying the translation and rotation of joint movements to the corresponding segments of its digital twin. Investigations using terahertz (THz) ray-tracing simulations for in-room environment scenario are carried out for different human gaits and velocities at 300 GHz center frequency. Moreover, upon comparing animated postures of this human model with its digital twin which executes the movements according to the measured data from the inertia sensors, the need to record human individual postures is stressed in order to simulate the interaction between humans and technical equipment whereby small changes in human movement might trigger a major impact.

Cardiovascular disease is the leading cause of premature death globally. There is emerging evidence that the morphology and composition of atherosclerotic plaques is a more reliable predictor of acute plaque events than the degree of coronary stenosis. The currently used plaque diagnostic methods - x-ray angiography, computed coronary tomography angiography, optical coherence tomography (OCT) or intravascular ultrasound (IVUS) - are not capable of delivering accurate risk prediction. Thus the development of a novel and minimally invasive method of assessing plaques and their risk of causing acute events remains critical. One promising alternative is electrical impedance spectroscopy (EIS). Previous studies focused on contact measurement of plaque structures. Herein we investigate plaque detection and non-contact sensing ability with the plaque, aorta and blood phantom models. The results show the feasibility of using this modality as a plaque detection method in non-contact intravascular sensing and imaging.

Electronic devices equipped with high-resolutions display panels with the capability of high-speed, low-latency wireless communication are becoming increasingly popular. State-of-the-art wireless generations such as 5G, ultra-wideband (UWB), Wi-Fi 6 will rely on the implementation of efficient and intelligent radio antennas. However, the evolution of display panels such as foldable, stretchable, breezeless and large-screen displays have triggered the need to reevaluate antenna design strategies and methodologies. Classical antenna theory professes the radiation efficiency of an antenna to be proportional to the effective antenna volume. Given the fact that conventional antennas have been designed and implemented as independent components, antenna radiation and performance suffers as the antenna real estate is further decreased amid the increased portion of display panels within a device. This eventually leads to performance degradation of wireless devices which use the latest display panel technologies. This talk introduces the original concept of incorporating a transparent, optically invisible antenna circuitry within the display panel. Denoted as an Antenna-on-Display (AoD), this approach demonstrates that electromagnetic fields can be generated and controlled within the view area of the display. This concept is applied and demonstrated across a variety of different wireless standards such as GPS, Wi-Fi and millimeter-wave 5G and 6G.

From a theoretical and conceptional point of view, active array technology can be the basis for powerful and flexible antenna solutions for many applications. However, when it comes to the industrial realization, there is always a danger of ending up with a very complex system, suffering from e.g. high material costs, a complex assembly process and/or a heavy weight. Therefore, the industrial design process of active arrays starts with a careful selection of the material baseline in combination with an application specific tailoring of the antenna to the functionality needed. The design process applied is very much based on efficient 3D EM modelling of the whole system including all details of the antenna and the integration scenario. By using a modular approach, one can combine high design and tailoring flexibility with affordable production costs. The presentation gives insight into today's industrial design process and shows several examples of active array antennas realized e.g. in aluminum, plastic molding, organic substrate and LTCC. Based on latter systematic design process, the active array technology can provide very powerful industrial solutions at medium complexity and acceptable costs.

Reliable, high-speed connectivity with low energy consumption and latency is a fundamental need in data centers. The use of wires and optical links in current data centers precludes adaptive scalability and suffers drawbacks in terms of assembly cost, airflow blockage, maintenance, and lengthy service time. It has been envisioned that future data center interconnects would alleviate the aforestated problems and introduce a higher data rate and low-latency communication. In this talk, we will discuss various opportunities, challenges, and current experimental trials in an effort to accomplish this in future data centers with the use of wireless Terahertz (THz) technology. We will show how these performance objectives can be achieved by affording data rates of up to 1.5 Tera-bits-per-second (Tbps) at a low power consumption of about 2.75 pJ/b (Energy-per-bit value), latency of 4.78 ns and good signal fidelity that ensures a Bit-Error-Rate (BER) of 10−12.

The C to Ku frequency bands currently in use are becoming more and more crowded, whereas there is still a need for new services. Increasing the frequency to Q/V band increases the degradation due to the troposphere: not only rain, but also clouds, gases and turbulence are affecting the propagation. Radiowave propagation models for geostationary satellites links are available worldwide in ITU-R Recommendations. In the absence of Earth-LEO propagation measurements, however, only statistical models are available for non-GEO links and they were not validated against measurements. Numerical Weather Prediction models produce meteorological parameters that can be used to simulate the degradation of the GEO and non-GEO earth-space links. The talk will illustrate the results already obtained, their validation with existing GEO measurements and finally underline the potential of this method but also its limitations.

In the present paper we introduce simultaneous multi-band measurements at sub-6 GHz and two mm-wave bands with the objective of characterizing propagation for multi-band channel modelling purposes in industry scenarios. The marginal power profiles show that the dominant scatterers are common in the different frequencies. In addition, a relation of decreasing average delay and angular spreads with increasing frequency is observed. The different measured parameters are contrasted with the 3GPP model for indoor factories.

Measurements at 5G Frequency Range 2 (FR2) and beyond (41.5 GHz and 60.5 GHz) were carried out in order to study how space diversity can be applied to compensate for the challenging conditions at those frequencies. Several indoor scenarios were analyzed, including Line-Of-Sight (LOS) and Non-Line-Of-Sight (NLOS). When considering an outage of 1%, space diversity was found to be a suitable impairment mitigation technique. Improvements in signal signal levels with increments from 7.53 dB up to 14.37 dB, depending on the case study in question were observed.

Propagation graphs (PGs) are a spatially consistent model for multiple-input multiple-output (MIMO) and potentially ultra-wideband (UWB) wireless channels. In this work, we extend the PG model with an existing theory for UWB channels to incorporate the frequency dependency of the involved antennas. The resulting model has very few parameters and allows fast channel simulations in a scattering environment. Static in-door UWB measurements were conducted using a vector network analyzer and virtual antenna arrays to confirm the validity of the presented model. A qualitative comparison between the simulation results and the measurements shows that the presented model fits the considered propagation environment very well.

The use of EHF (30-300 GHz) in terrestrial radio links is one key element in future 5G and beyond 5G technologies. Rain attenuation is the major impairment affecting radio links operating at this band. Due to the lack of experimental measurements for the EHF band, one approach is to estimate rain attenuation by using information about the rain DSD. In previous works, rain attenuation and its variability have been estimated up to 200 GHz by applying the Mie Theory to experimental DSD, considering spherical raindrops. This work goes a step further and provides the derivation of rain attenuation using a non-spherical drop model. To that aim, full-wave electromagnetic software is used to derive the extinction cross section of non-spherical drops excited with horizontal and vertical polarizations. The results show that at such high frequencies the differences between polarizations are not large but the variability of rain attenuation is not negligible.

For the first time, TR experiments are conducted at 273 GHz with a bandwidth that can be as large as 2GHz. Spatio-temporal focusing of pulses are observed through different complex media. The first medium is a 1 m long and 10 mm diameter straight hollow cylinder. The second one, is a 5 m long and 12 mm diameter curved waveguide. Finally, we present results obtained in a cavity of 72cm3 that leaks through a copper grid. The best focusing is observed with the longer waveguide. These results may open the path for electronic beam steering of EM pulses.

This paper proposes a solution that allows reducing the obstruction from the mobile phone frame to electromagnetic waves in two bands of the mm-wave spectrum. This response is obtained by etching longitudinal corrugations of two different lengths in the metal frame. The corrugations are inspired on the hard surfaces principle, which supports the propagation of electromagnetic waves on metal. The proposed structure is matched to a 50-Ohm source in the following bands: 25.4-27.7 GHz, 28.7-29.9 GHz, and 36.4-40.3 GHz. The realized gain of the mm-wave array with the corrugated frame is higher than the one of the array in free space in the majority of the operating bandwidth. The proposed solution can increase the gain of the array with a normal frame up to 10 dB.

This paper discusses the design, fabrication, and measurement of a two layer, 2X10 elliptic, microstrip series fed antenna array operating at 28 GHz 5G and mm-wave user equipment. A branch line coupler (BLC) was used as a feeding network which generates three beams. The peak gain value of each beam was 13 dBi at 28 GHz. The gain value was above 10 dBi within a beam coverage of -45 to 45 degrees, and the peak gain value for the 26.5 GHz to 29.5 GHz band was above 10 dBi. The impedance bandwidth of the proposed design was below -10 dB in the 26.5 GHz to 29.5 GHz band. The dimensions of the 2 X 10 antenna array with coupler were 80 x 40 x 0.203 mm3 on Rogers RO4003 substrate. This design is suitable for 5G mobile user applications due to low cost and compactness.

A nine-element antenna array is presented. It has a flat-top radiation pattern and is matched for use in both the 24.25-29.5 GHz and the 37-40 GHz frequency bands for 5G mm-wave systems. The application of this antenna is for use in over-the-air test systems for mm-wave base stations.

When a dipole is placed close to a ground plane, the induced currents on the ground plane are opposite to dipole currents making the entity a poor radiator. This paper presents a dipole antenna design at the ground distance of only 0.5 mm (0.04(math\lambda_0) at 25 GHz). The dipole-ground interaction is tuned with reactive loading so that induced currents on the ground and those on the dipole arms contribute additively in the far field. Thus, the radiation efficiency is significantly improved when the total current reaches the peak. The value of the components are obtained through a quick circuit optimization and can be easily converted to a discrete form. This method is verified in the simulations with both the lumped and discrete elements. The results show that the proposed antenna has reached a good radiation efficiency, realized gain, and impedance matching at 25 GHz.

A realization of the quasi-optical (QO) feed concept for linear millimeter-wave (sub-)array antennas is demonstrated in gap waveguide technology. The proposed feed architecture employs an input transition from a ridge gap waveguide (RGW) to a groove gap waveguide (GGW), a radial (H-plane sectoral) GGW section, and a transition to an output RGW array. A design decomposition approach is presented to reduce simulation complexity. Several 20-element QO feed implementations are investigated at W-band demonstrating a 20% relative bandwidth (85-105 GHz), 0.5 dB insertion loss, and a capability of an amplitude taper control within the 10-20 dB range.

A sensor using a Defected Ground Structure (DGS) based on the matryoshka geometry is described. The main idea is to take advantage of the miniaturization and selectivity characteristics of the matryoshka geometry. The proposed DGS sensor geometry is outlined, and initial design equations are presented. A prototype was fabricated and characterized. For the empty sensor, when comparing numerical and measured results, a very good agreement is achieved. Moreover, the resonant frequency determined using the proposed design equations represents a good agreement too. In order to verify the matryoshka DGS sensor sensibility, a mixture of distilled water and isopropyl alcohol was characterized and a calibration curve achieved. Finally, the matryoshka DGS sensor is compared with a dumbbell DGS sensor occupying the same area, confirming the miniaturization and selectivity characteristics of the matryoshka geometry. The achieved results and characteristics instigate the matryoshka DGS sensor research.

Due to increasingly complex and automated manufacturing processes, the demands on the control parameters of these processes are also increasing. One parameter is the fill quantity of e.g. liquids in production plants, whose precise determination is ever of growing importance. Up to now, the exact level determination under difficult conditions, such as high ambient temperatures, has been a particular challenge. This paper demonstrates a novel method by which an M-sequence UWB radar can determine levels of low-permittivity materials in small metal containers. For this purpose, hot melt is used as an example. Thus, the influence of large temperature differences on the long-term stability of level measurement can also be investigated.

Monopiles are one of the most common foundation types for offshore wind turbines (OWT). They are subject to large bending moments which can lead to crack formation and ingress of water in the grout that connects the monopile foundation to the rest of the OWT via a transition piece. It is therefore of great interest to be able to continuously inspect the grout. To characterize the grout material used in this paper in terms of its dielectric properties an open-ended coaxial probe is utilized. In addition, a simplified laboratory demonstrator is designed and manufactured to enable first radar measurements. Grout-filled TEM horn antennas and a stepped-frequency continuous wave (SFCW) radar are purpose-built to enable measurements from 100 MHz to 2 GHz. The antennas are characterized and compared to the simulation. Finally it is shown that water can be detected through one meter of steel-lined grout by analyzing differential signals.

Open-ended coaxial probe (OCP), as a widely used conventional technique for dielectric spectroscopy in the microwave and millimeter-wave regime, suffers from two difficulties when applied to high-permittivity solids. They include high sensitivity to minute gaps between the probe and sample, and reflections from probe boundary when layered samples are measured. In this contribution, we present first a calibration algorithm that aims at measuring the effective air-gap between the probe and sample. The result of this algorithm is later used in the OCP measurement process to cover the effect of this air-gap. Second, we introduce using a lossy platform below the thin sample to mitigate the inaccuracies caused by probe truncation. An exemplary high-permittivity thin sample is outlined and measured using both conventional and new algorithm, which demonstrates a considerable reduction in measurement error when the proposed procedure is followed.

In this paper, dielectric properties of thin-film materials in Fan-out Wafer Level Packages (FoWLP) used for the development of 5G mmWave Antenna-in-Package (AiP) modules are measured in the 5G New radio (NR) frequency bands (26.5-29.5 GHz and 37-40 GHz) in dependency on temperature (0°-150°C).

As an alternative to delta and delta-square patterns usually exploited in the receive mode for the localization of targets, we propose herein to use 'orbital angular momentum' (OAM) antennas. By so doing, it is possible to effectively generate a single isolated null of the pattern rather than a whole row (and/or column) of zeroes in the spectral plane, so that a better localization can be achieved. General considerations are first given showing that the 1 (or -1) OAM vortex order is the best-suited one for such a goal. Then, a Convex Programming synthesis procedure maximizing the localization performance by relying on OAM vortices is given and tested.

Indoor source localization becomes a major challenge for many applications such as beam-steering or MIMO communication. We propose to design a single port Rx antenna based on metamaterial dedicated to angular localization of a wideband source. We take benefit of the strong frequency dependence of the radiation pattern of an open balanced Composite- Right-Left-Hand structure to design the proposed antenna. We experimentally demonstrate with a microwave prototype that an efficient angular localization can be achieved with this approach.

This paper discusses the design and performance of an eight-arm sinuous antenna for analog and digital direction finding (DF) systems. The multimode and dual-polarized capabilities of the eight-arm sinuous are utilized to achieve wideband angle of arrival estimation independent of the incoming signal polarization. The performance is evaluated for the classical analog amplitude/phase comparison and the importance of mode 3 to achieve more accurate estimation is highlighted. Also, the Cramér-Rao lower bound (CRLB) is used to evaluate the performance of the proposed design in the context of a digital receiver backend. The performance of the antenna is experimentally verified over the 1.5-4.5GHz frequency band and low estimation errors are demonstrated over wide field of view

An existing 4.6 meter Cassegrain antenna at the Ottawa Research Lab was modified to augment a passive RF observation space domain awareness capability currently under development. A commercial-off-the-shelf S-band flat panel antenna is now used as a feed to provide joint passive oneway Doppler and interferometry measurements of satellites in Earth orbit. These measurements can be used to improve orbit determination accuracy and contribute to space domain awareness in a very economical fashion. Near-field measurements of the feed, numerical simulations of the feed in the presence of the main and sub- reflectors, details on the RF front-end, and experimental Doppler and interferometry results are presented.

The performance of a multi-mode direction finding antenna depends on the selection of the utilized characteristic modes. A numerically efficient way to determine the correlation of the incident fields reconstructed from these characteristic modes is introduced. These correlations are evaluated for several directions of arrival (DoAs) and assembled in a correlation matrix. This procedure is repeated for different combinations of characteristic modes and the Frobenius norm of the correlation matrices is used to determine the combination of modes best suited for a defined direction finding application. An example setup as well as computational results are provided and it is shown that the proposed method provides insight into the physical behavior of the direction finding setup.

The design of a leaky-wave antenna array in the L-band is presented. The array has been developed to feed a large reflector that is part of a SAR system for Earth observation. The basic element of the array is a differentially fed patch antenna that excites the leaky modes in a resonant cavity that is defined by a metasurface. The performance of a 3x3 sub-array has been studied and is presented in this paper, as well as the individual element. Important aspects of the design that affect the overall performance of the array are discussed together with the measured results of the fabricated prototype.

The European Large Deployable Reflector (LDR) antenna underwent RF test in November 2020, becoming the first 5.1 m antenna in light mesh technology developed and measured in Europe. In this paper we present the correlation between the measured and predicted antenna patterns at 10.65 GHz.

New radiometer technology is a key enabling factor for the upcoming new generation of space missions; earth observation applications, with the use of cubesats and nanosatellites, will benefit greatly from the insight into our own planet these sensors can offer. In this paper, a four-armed cavity-backed radiometer spiral antenna is designed and simulated to capture the 183GHz ±5GHz water absorption line, fundamental for measuring moisture levels in the atmosphere and evaluating the effects of climate change in our planet. Due to the manufacturing difficulties involved, a scaled design centered in 7GHz is also provided. This scaled design is manufactured and measured as a way to validate the EHF design.

This paper reports the design and implementation of a circularly polarized microstrip array antenna operating in C-band. The antenna was designed to upgrade a C-band active reflector to be used with the ESA Sentinel-1 satellite SAR. The use of circular polarization improves the exploitation of the single polarization active reflectors allowing their use for the complete set of linearly polarized radar images available from the SAR acquisitions. This improvement can be done simply by replacing one of its two antennas. High gain, low cost, and a fine axial ratio are the main requirements of this prototype. Results show a good agreement between simulations and measurements, moreover, the close-range operational test done with the active reflector using the proposed antenna demonstrates the feasibility of the idea described in this work.

The electrical architecture of a multibeam hybrid Synthetic Aperture Radar system is presented. The SAR Instrument is a hybrid analogue-digital multichannel radar system intended to provide high resolution and wide swath coverage. To achieve that the system is composed of a large oversize reflector fed by a multibeam CORPS (Coherently Radiating Periodic Structure) feedarray. The architecture of the system corresponds to a distributed semiactive digital configuration that extends along the feedarray length. The paper presents the main characteristics of the electrical architecture of the OLAF SAR.

A detailed analysis of the performance of traditional machine learning and deep learning techniques applied on a representative classification problem of millimeter-wave (mmW) images is presented in this paper. The dataset for training and testing are generated via a developed coded aperture computational imaging physical model. The models are tested with both synthesized as well as experimental data, generated from the physical model and a mmW handheld imager, respectively. Upon testing, accuracy of 90% is observed in the case of CNN classifier. Also, an inference speed test is conducted on all three algorithms. It was observed that CNN is the fastest to predict classes for all of the test samples. These findings establish the fact that when it comes to image classification, CNN-based classifiers perform better than any traditional machine learning algorithms with more accurate and faster predictions, paving the way for various real-time applications such as automatic threat detection.

With the development of irregular antenna array, some fast methods are no longer applicable, and a lot of computation is required for calculation and optimization. This paper proposes a two-dimensional nonuniform fast Fourier transform (2D-NUFFT) method to calculate the nonuniform array pattern, as well as for nonuniform field points, achieved by two steps. First step is a rearrangement of the nonuniform array into uniform oversampled grids. Second step contains the general uniform FFT, as well as an approximation for computing the values at the nonuniform field points. The calculation amount of the proposed method is analyzed which shows superior effectiveness especially for large-scale arrays. The pattern of the nonuniform array example is calculated using the proposed method, with numerical results showing the effectiveness of the applied algorithm.

We present an accelerated source reconstruction method well suited for use in antenna diagnostics applications. A reformulation of the inverse electromagnetic scattering problem has been implemented numerically and is solved using a higher-order method of moments (MoM) discretization. The novel implementation achieves asymptotically better scaling in terms of computational time and memory requirements in comparison to commercially available source reconstruction solvers. A test case of a reflector antenna on a satellite platform was used to evaluate the new method, and significant improvements are observed in comparison to a commercial state-of-the-art solver in DIATOOL 1.1.

Reverberation chambers (RCs) are proposed as repeatable test environments. Often, the mode stirrers inside a RC are operated stepwise, whereby the essential measurements are performed under quasi-static conditions. However, mechanical mode stirrers usually vibrate when arriving on a new position. The influence of this mechanical vibration on the repeatability is analyzed in this paper and the results open up opportunities for future enhancement of mode stirrers movement.

This work investigates the accuracy of the open-ended coaxial probe technique for measuring the dielectric properties of well-characterized liquids. Two different de-embedding models are used for retrieving the properties of materials under test considering different calibration standards. Liquids of interest were both simulated and measured. Optimal calibration setups for achieving good level of accuracy are proposed.

Recently it has been proposed the introduction of an additional layer placed below the Physical Layer of the OSI model, called the "Deep Physical Layer" (DPL), to analyze the communication process at the electromagnetic field level. While the transmission process at the Physical Layer level is focused on bits, information at the DPL level is modeled in terms of distinguishable configurations of the electromagnetic field. In this approach, the numerous solutions proposed for 6G, which include intelligent modifications of the propagation environment, can be seen as "data processing" at the DPL level able to preserve information lost in previous generations of cellular systems.

The smart electromagnetic environment (SEE) is a rapidly evolving paradigm aiming at revolutionizing the design of next-generation mobile communication systems. It is founded on the main idea that the propagation scenario should be no more regarded as an impairment to the overall system performance, but rather as a powerful additional degree-of-freedom (DoF) for tailoring the complex EM propagation phenomena towards an enhanced quality-of-service (QoS). Current trends and future perspectives of such an emerging framework are discussed to provide an overview of the most recent advancements in this field as well as to identify open challenges and promising future tracks of research.

The concept of smart electromagnetic environments has been proposed in the last years as an effective strategy to overcome the detrimental effects of the propagation scenario on the efficiency and robustness of communication systems. Specifically, a smart electromagnetic environment is a complex and properly designed environment able to maximize the efficiency and capacity of one or more communication channels. The environmental engineering has been made possible thanks to the new degrees of freedom introduced by metasurfaces, which allow generalized field transformations and play an active role in achieving unprecedented system performances. In this contribution, we present and discuss some recent applications of metasurfaces in the antenna frame and contextualize them in the scenario of next-generation wireless systems. We show their potentialities in overcoming some undesired effects introduced by conventional environments in wireless communications and discuss their crucial role towards the practical implementation of a smart electromagnetic environment.

For radio base stations enabling massive multiple-input multiple-output (MIMO) and beamforming technologies, using the highest possible power and gain values for all beams result in a very unrealistic assessment of radio frequency (RF) electromagnetic field (EMF) exposure. A more accurate approach, namely the actual maximum approach, has been developed in the past few years and recommended by international RF EMF exposure assessment standards and regulatory bodies. In this paper, we summarize the recent EMF research studies on this approach, including statistical modeling studies, measurement campaigns, and related applications, such as the usage of time-averaged power monitoring and control features.

IRS can control the reflection of electromagnetic wave, so the deployment of IRS can adjust the channel conditions to enhance the coverage and throughput in the 5G evolution networks. Since the IRS is only capable of passively reflecting the received signals, its path-loss modelling method is different from existing two-hop communication networks, such as repeater, or relay. In this paper, the path-loss model for IRS in real urban scenario is proposed. Based on the theoretical analysis, the novel measurement methodology is proposed that the path-loss channel measurement campaign can be divided into separate measurement and cascade measurement, so that the measurement efficiency is dramatically improved under the constraint of modelling accuracy. The measurement data at 3.7GHz verifies the accuracy of the proposed IRS path-loss model with the RMSE as 2.33dB. The work investigated in this paper could be the foundation for IRS-based network link budge calculation and system level evaluation.

The design of antenna arrays forming flat-top beampatterns prefers robust and computationally efficient methods. These features are usually met by analytical techniques or simple optimization procedures. On the other hand, in the flat-top array design, a common requirement is the ability to control the beampattern width and sidelobe level. However, it usually brings the excitation coefficients with high or unpredictable dynamic range ratio. In this paper, the authors propose a straightforward method for the design of symmetrical flat-top arrays with controllable dynamic range ratio. The method is based on the quadratic transform of a Gaussian excitation to the array having maximally flat main beam. In addition, the method deals with zero coefficients, whose positions are used to control the dynamic range ratio. As a special case, flat-top Gaussian arrays with minimum dynamic range ratio can be obtained.

Optimization-based methods for pencil-beam design often incorporate controlling the dynamic range ratio (DRR) of excitation coefficients. However, constraining the DRR causes the deterioration of sidelobe region, in which some lobes may rise and even exceed design specifications. To prevent such behavior, additional requirement can be specified to constrain maximum sidelobe level (SLL). This paper presents a global design of pencil beams with specified DRR and SLL. The design is based on branch and bound method that utilizes convex optimization and feasibility analysis for tree pruning. As a case study, the paper considers design of pencil beams optimum in L1-sense to which DRR and SLL constraints are added. The resulting beam patterns exhibit low DRRs and decreasing side lobes.

The classical noise wave theory is employed in the field of Coherently Radiating Periodic Structures (CORPS). The coherent properties of these type of networks allow the distribution of a signal across the network and the in-phase recombination of each distributed component at an output port. Whereas these distribution and recombination processes are coherent for the signal and hence do not incur in power loss, the intrinsically incoherent noise contributions incident at the port terminations are not sum coherently. This is especially significant in presence of incident noise powers much larger than the intrinsically generated thermal noise. As a result, an enhancement in terms of Signal-to-Noise Ratio (SNR) is demonstrated analytically by means of noise wave theory. The maximum achievable SNR enhancement depends on the internal structure of the CORPS network. Validation of the proposed theory is provided by means of a commercial circuital software.

The nulls in antenna radiation patterns can show the non-trivial Riemann zeta zeros. Here is an attempt at simulating an antenna design that visualise these zeros

This paper presents the design, optimization and simulation of a novel 12x12 W-Band waveguide slotted array antenna. This antenna is based on stacked glide-symmetric metal sheets fed by a groove gap waveguide (GGW). This paper also proposes a new unit cell. The suggested unit cell has serpentine-shaped holes in a glide-symmetric configuration with the goal of minimizing the separation between parallel waveguides. To demonstrate the viability of the proposed unit cell, a 12x12 W-Band waveguide slotted array antenna at 92 GHz was designed and simulated. The results show that the proposed slot array antenna has a reflection coefficient below −10 dB within 91.3 GHz to 93 GHz, and the peak directivity and gain are about 29.7 dBi and 28.8 dB, respectively, at 92 GHz.

Resonant Bessel-beam launchers are azimuthally invariant structures characterized by a circular grounded dielectric slab with an isotropic metasurface on top. Previous works analyzed the launchers performance for some specific cases, assuming TE or TM polarizations, inductive or capacitive metasurfaces, cavities with sub-wavelength or half-wavelength height. We show here with both theoretical and full-wave results that the inductive or capacitive nature of the metasurface has a fundamental role in the radiating behavior of these devices. Results are reported for the relevant TM-polarized case, considering air-filled, half-wavelength thick cavities. The extension of this analysis to the TE-polarized and dielectric-filled case will be discussed at the conference.

In this communication, a half-mode waveguide based on Gap Waveguide technology for rapid prototyping is presented. A power divider is designed for demonstration purposes. The power divider is constructed from two non-contacting metal pieces. The horizontally-polarized power divider is housed in the bottom piece. The height of the groove is about half that which would be required to propagate the fundamental mode. The top cover is a uniform pinned surface that acts as a High Impedance Surface (HIS) over the groove of the bottom plate. The simulated reflection coefficient shows values of less than -15 dB in the bandwidth of interest (28 to 31 GHz). This design stands out for its ease of fabrication and opens a horizon for cheaper and more robust GW designs for mass production.

The use of an eutectic alloy composed of gallium, indium and tin (known as Galinstan) is proposed to implement electronic reconfiguration at different levels in reflectarray elements. This material allows to change the shape of the elements of the array, with direct impact on the reflected phase, frequency of operation or polarization. These properties can be independently or simultaneously optimized though the reshaping of the conductive part of the element. This contribution is focused in demonstrating the viability of Galinstan as a reconfiguration element. The microfluidics-based technology is presented as a key actor in the implementation of these kind of antennas, offering a wide range of micro-devices as valves, mixers, pumps or lab-on-a-chip systems, inherited from years of study in other fields, such as chemistry, biology and medicine. The proposed method opens a promising avenue to reconfigurable reflectarray elements.

Anticipated by 2035, a trillion wirelessly connected Internet of Everything (IoE) devices will be deployed. Therefore, sustainable and low-cost antennas are crucial for enabling an environmentally-friendly IoE. We present the first non-metallic carbon-based microstrip patch antenna implemented on textiles for wearable applications. The antenna is fabricated on a standard felt/woven-polyester fabric substrate using stencil casting and demonstrated for S-band applications. The antenna maintains a wide 10% fractional bandwidth from 3.16 to 3.49 GHz and achieves at least 30\% radiation efficiency, 10.4~dBi measured directivity, and 6.1 dBi measured gain. It is demonstrated that non-metallic carbon-based antennas are suitable for future wearable IoE applications.

This work presents a novel concept of three-dimensional (3-D) full metal Frequency Selective Surfaces (FSS) that is located inside of a circularly polarized conical horn antenna to add frequency filtering properties without an external structure for X-band space applications. Two parallel thicken sheet patches are connected by a self-supported mesh at their centers. In the final step, the designed 3-D FSS is located inside a conical horn antenna to analyze its filtering response, as well as the possible interference of the designed isolated FSS structure when it is located inside the internal profile. The simulated results of this idea prove its appropriated performance for X-band applications, with a 10% fractional bandwidth for a 20 dB minimum return loss value. The antenna directivity is higher than 15 dBi in a field view of ±8º, with axial ratio below 1.5 dB from 7 to 8 GHz.

In conventional ray tracing methods, diffraction calculations for wedges are typically based on the uniform theory of diffraction (UTD). However, UTD is both inaccurate and computationally expensive in the calculation of multiple diffractions. In order to mitigate these shortcomings, a Huygens' principle based method is proposed as an alternative or extension to the conventional UTD. This method captures rays on properly chosen Huygens' surfaces and creates equivalent emitters for subsequent secondary ray launches based on the captured rays. Despite the extra effort of creating a Huygens' surface, compared with UTD, this method has considerably improved flexibility in handling complex geometrical shapes and it preserves the accuracy over multiple diffractions. Furthermore, by properly choosing the Huygens' surface and equivalent emitters, both computational complexity and accuracy can be controlled.

Deterministic channel emulator applicable in both static and dynamic scenarios are essential for testing a performance of a large-scale wireless communication system, such as cyber-physical system, with high accuracy. Despite providing a better accuracy than a stochastic approach, deterministic channel simulation such as ray tracing (RT) is time-consuming especially in the dynamic scenario. Therefore, implementing such deterministic approach in the channel emulator is challenging due to hardware constraint and real-time computation requirement. In this paper, a grid-based architecture is proposed to realize the deterministic channel emulator. Here, RT is utilizing to only generate spatial channel parameters at specific grid nodes and stores in the emulator database. Time-variant channel of a moving mobile station is synthesized by interpolating parameters of the tapped delay line channel at neighbor grid nodes, which has been converted from the spatial ones. Basic building-block of the proposed architecture and challenges will be addressed in the paper.

In Wireless Body Area Networks, the subject characteristics are among the main sources of the channel variability. The objective is to highlight statistically the influence of the anthropomorphic characteristics on the on-body channel. We have simulated five radio links on five homogeneous men subjects with different morphological characteristics. Experimental results obtained for some radio links have been used to support the relevance of the simulations. Within the framework of this first semi-quantitative approach, this communication is limited to the modeling of the Path Loss as a function of two quantitative morphological parameters that are the BMI and the Waist Circumference. The objective is to identify the main trends and to extract "semi-quantitative" models giving the orders of magnitude of the variability for each radio link. The latter typically ranges from 4 to 10.5 dB for the phantoms considered. The importance of the variability obtained justifies the interest of this analysis.

Due to its broadcast nature, the wireless channel cannot be really private, i.e. restricted to the intended users only. Rather, it can always be available also to some unauthorized outsider, and, thus, security in wireless communications is crucial. Protection of communications from possible eavesdroppers is usually achieved through standard cryptography schemes, which nonetheless may not always represent the best solution due to their complexity and power consumption. Physical Layer Security, in particular Secret Key Generation, leverages the fading/dispersive properties of the wireless channel to distill encryption keys with limited computational effort. In this study, ray tracing propagation modeling is proposed as a tool to investigate the performance of the physical layer approach to communications security, thanks to its capabilities to model the channel statistics and the more flexibility compared to a measurement campaign.

With the unprecedented data rates targeted by 5G+, the attention on Free-Space Optics (FSO) is reviving. FSO provides point-to-point wireless connectivity over large and unlicensed bandwidths. However, the severe channel attenuation due to fog limits the maximum path length of optical links when high-availability targets are required. Here, we quantify the effect of radiation fog on the optical channel at two wavelengths, namely 1.550 (\mu)m (near-IR), where most of commercial FSO system operate and 10.6 (\mu)m (mid-IR). The approach adopted here is based on the particle size distribution of fog, which is modelled by both mono-modal and multi-modal functions. if radiation fogs, typical of mid-latitude continental regions are considered, the ratio between the achievable path length at mid-IR and at near-IR ranges from 2 to 3, but it can be much higher due to the sensitivity of mid-IR radiation to the microphysics of fog.

In this paper a new topology for high gain antenna aperture with fixed broadside radiation is presented for 140GHz band. In the proposed structure, two symmetrical sets of leaky wave radiating slots are placed back to back on the broad wall of a metal parallel plate waveguide. A Corrugated surface is also applied in the feeding waveguide in order to deal with the grating lobe problem. The designed aperture provides proper fixed broadside radiation with 27.8-30.2dBi directivity over 142-148GHz frequency band. The aperture efficiency of more than 60% up to about 80% is also obtained over the most of desired band.

This paper presents a dielectric image line antenna array at W-band. The array consists of four dielectric image line rod antennas, fed by an image line multimode-interference power divider, which divides power without the use of y-branches. The whole array, including the power divider, is machined from one piece of low permittivity Rexolite, which is mounted on a ground plane. Gain is up to 21 dBi and the bandwidth is 15 GHz, from 93 GHz to 108 GHz with a nearly frequency-independent pattern. The image line topology proves to be an attractive alternative to fully dielectric arrays, since integration with conventional circuitry and increased gain is possible.

This paper presents a wideband dual-fed/dual-polarized sub-terahertz (THz) array antenna design and D-band measurement system setup. The designed array is 4x1 linear array operating from 136 to 148 GHz. The array is fed by vertically constructed corporate feeding network, and it is fabricated through printed circuit board (PCB) using modified semi-additive process (mSAP). For wideband impedance matching of the antenna element, stub-loaded proximity coupled stacked patch antenna is introduced. By employing two or more open/short stubs on vertical via transition of the proximity coupled line, wideband input impedance matching is achieved, and these stubs can be easily integrated into the antenna element without increasing the element size. A customized probe station is also built to enable probing from the bottom side of the probe station. The maximum gain is measured as 9.1 dBi in the proposed D-band measurement system.

This paper presents the synthesis, design and characterization of a centrosymmetric transmitarray antenna operating at 300 GHz. A broadside pencil beam with reduced sidelobe levels is obtained by fixing the illumination (i.e. feed and focal distance) and using a phase-only array synthesis procedure. The optimal aperture phase distribution is determined by means of an iterative convex optimization algorithm using semidefinite relaxation. Based on this distribution, a 400-element transmitarray comprising eight different unit cells is designed at 300 GHz, fabricated using low-cost printed circuit board technology and characterized. The measured results provide a first experimental validation of the synthesis approach.

We present here the design of a broadband antenna array for photonic beam-steering at W-band. The array unit-cell consists of two stacked microstrip patches that are cavity backed, and fed by aperture-coupling using an hourglass slot. The unit-cell shows a simulated impedance bandwidth of 37% for SWR<2 from 77 GHz to 112 GHz, thus covering most of the W band. The feeding network is designed using a low-loss Substrate Integrated Waveguide (SIW) and respects nearly the same bandwidth as the unit cell for a total SWR<2. Therefore, the structure is well-suited for fabrication by PCB technology. The final array is composed of 4 sub-arrays of 2×8 unit cells and exhibits a broadside directivity of 26 dBi. Each sub-array is expected to be fed by a Uni-Traveling-Carrier (UTC) photodiode, which enables power combining to overcome the low emitted power at mm-waves and also the use of optical phase shifters in the antenna architecture to achieve a +/-5° beam steering with reasonable grating lobes.

Breast cancer is most common, so early diagnosis of tumors is wished for. Microwave (MW) and ultrasound (US) are non-invasive, non-ionizing, low-cost, and can be run without registration for free pending breasts. MW is to yield high-contrast images of low resolution, the converse with US, with the benefit of the common breast structure. That is, fusion of MW and US data should produce images with both high contrast and high resolution. Here a Bayesian formalism is chosen to that effect (Variational Bayesian Approximation or VBA), edges as hidden variables, a number of hyperparameters involved as expected. Once the mathematics sketched, one insists on imaging of a MRI- derived breast model, a tumor added into it. Comparison with a joint edge-preserving contrast source inversion (JCSI-EP) in a deterministic framework will illustrate pros and cons of VBA.

Electromagnetic imaging of dielectric targets at microwave frequencies needs dealing with an inverse problem, whose solution process is further complicated by the unavoidable presence of model error. In this work, the adoption of a neural network based on long short-term memory cells is introduced for the compensation of such an issue. In particular, multistatic measurement settings are considered here for the first time. The proposed network performs a preliminary processing of the scattered field, which is then passed to a multifrequency nonlinear inverse-scattering algorithm formulated in non-Hilbertian Lebesgue spaces with non-constant exponents. The approach is initially validated in a simulated environment.

Microwave imaging can represent an alternative for in-line inspection of food products, to reveal the presence of possible foreign bodies that may have contaminated the product during the transformation and/or packaging stages. To this end, a microwave system specifically meant for such purpose has been recently proposed. With respect to this device, a novel imaging strategy is presented, which allows one to build the image of the target without the need of a contaminant-free item used as reference sample. The idea is still to perform a differential imaging taking advantage of possible symmetries of the object under test with respect to the imaging system. These symmetries only occurred in a contaminant-free item, while are broken by the presence of an inclusion, thus revealing their presence. A quite common case is that of food packaged in circular plastic/glass jars. A simple numerical example is provided showing the capabilities of the approach.

When dealing with high nonlinear ISPs those the scatterers with high contrast and/or electrically large size, the nonlinearity would be increased significantly. The traditional iterative nonlinear inversion modeled by the Lippmann-Schwinger integral equation maybe trapped into local wrong solution or converge slowly and take lots of computation time. To circumstance above the challenges, a learning-assisted inversion approach in virtue of a new recently established contraction integral equation for inversion (CIE-I) is proposed with low computational cost. The preliminary profiles with low-frequency components can be got efficiently by the Fourier bases expansion with CIE-I (FBE-CIE-I) inversion method with only a few low-frequency components. In addition, in order to further speed up the inversion process and realize real-time imaging, FBE-CIE-I is accordingly replaced by a neural network to get the preliminary profile. Numerical examples are used to validate the effectiveness of the proposed method.

This paper proposes a numerical performance assessment of the recovery capabilities in the framework of microwave imaging via deep learning approaches. More in detail, aim of the analysis is the comparison among different convolutional neural network architectures in order to understand the impact of each parameter on the recovery performance for quantitative imaging. To support the analysis, some quality metrics were evaluated and a comparison with a conventional nonlinear approach is considered. The results seem promising, both in terms of computational time and recovery accuracy, especially in very noisy scenarios with a limited amount of data.

A per-iteration processing technique is applied to the Contrast Source Inversion algorithm to project a standard element-based contrast recovery step onto an alternative set of basis functions. For the grain storage monitoring application the alternative basis is advantageously chosen based on problem geometry to improve algorithm performance in resonant enclosures. Results for both synthetic and experimental grain storage problems demonstrate that the proposed basis projections significantly improve imaging results without requiring any major changes to the CSI gradient calculations.

In this paper, we apply the low-frequency data learning scheme to solve highly nonlinear inverse scattering problems (ISPs). High nonlinearity of ISP will cause the optimization process to fall into false solutions. To alleviate the nonlinearity, we can lower the operating frequency to reduce the electric size of the targets. However, low-frequency data are usually unavailable. Therefore, we apply a neural network named U-net to learn the low-frequency (LF) data from measured high-frequency (HF) data. The learned LF data is then inverted as an initial model for HF data inversion, which provides a reliable estimate for the targets and thus helps HF data inversion find the right solution. Furthermore, the U-net is fine-tuned by the inverted model to learn a more precise mapping from HF data to LF data. The effectiveness of this scheme is verified by both synthetic and experimental data inversions.

Food industries are paying increasing attention to new technologies for non-invasive assessment of products, in particular to detect low-density plastic, rubber, wood and glass, unlikely to be located by X-Rays. To this end, we propose a microwave-based device, exploiting the dielectric contrast between potential intrusions and the surrounding medium. This work aims to numerically assess this detection principle to water-based products that are, due to the medium losses, a challenging category at microwaves. An antennas array surrounds the object moving along the line, to monitor signal variations with respect to a reference. The working frequency is chosen by selecting a proper trade-off between penetration depth and image resolution. Then, a procedure, based on the application of the distorted-Born approximation is applied to reconstruct a 3-D image of the contaminant. Finally, the successful detection of a millimetric-sized plastic sphere is presented in the case of a commercial bottle filled with water.

In this paper, we propose a new approach for solving inverse scattering problems (ISPs) by applying the physics-informed supervised residual learning (PhiSRL) to embody the Born iterative method (BIM). Stemming from the mathematical link between the fixed point method and residual neural network (ResNet), PhiSRL fulfills the alternate iteration process of BIM by predicting the modifications of the candidate solutions regarding the calculated residuals. Thus, the proposed approach can perform the inversions of both data and models at the same time.The effectiveness of the proposed approach is further validated by the representative synthetic data.This paper provides new insights for designing the deep learning (DL) based methods with the knowledge of traditional computational electromagnetic (EM) algorithms.

In this contribution, we employ the orthogonality sampling method (OSM) for identifying small anomalies in real-world microwave imaging. It is known that the OSM works well for identifying a single anomaly under the specific location of a transmitter, whereas further improvement is needed for identifying multiple anomalies. Thus, we design an indicator function of OSM with multiple sources weighted by the incident field. Further, we demonstrated the improvements theoretically and experimentally.

This paper presents indoor radio channel measurements and models at D-band frequencies. A Line-of-Sight (LOS) alpha-beta-gamma path loss model is created based on indoor measurements up to 8.5 m in a laboratory and office room, resulting in a floating intercept α of 34.2 dB, PL exponent β 1.9 and frequency dependency γ 1.9. The penetration losses for wood, acrylic, polyvinyl chloride (PVC) and glass are measured, resulting in a respective loss of 8, 3.5, 3 and 12 dB/cm. Furthermore, attenuation due to desk objects obstructing the LOS path is found to range from 3 to 10 dB for one or more universal serial bus (USB) cables, and 8 to 13 dB for a computer keyboard and mouse. A laptop screen completely blocks the LOS path. Therefore, we measured the attenuation of the reflected path when the LOS path is blocked, and conclude that desk objects provide valid fallback paths.

In this paper, we analyze the EMF exposure, in terms of total received power, in the massive multiple-input multiple-output (MIMO) networks. With the recent deployment of 5G networks, the potential risks of electromagnetic field (EMF) exposure are gaining increasing attention. However, most of the current research that focus on the mathematical modeling of 5G networks ignore downlink power control. Therefore, we derive the framework of the average power received at nearest mobile terminal MT(_0) under max-min fairness power control using stochastic geometry. The total received power consists of three parts, useful signal, multi-user interference and inter-cell interference. We propose a tight approximation on the power control coefficient. Based on the proposed approximation, the framework on total received power is then validated by Monte-Carlo simulations. The results show that the average received power monotonically increases as the density of the base station increases and the number of users increases.

With the development of the smart railway, new services need to be supported by fifth-generation (5G) technology. Comparing to 5G technology, 5G-railway (5G-R) is more suitable for complex scenarios and strict requirements of rail transit, with the potential frequency band of 2.1 GHz. An indoor server room containing servers and train control systems is a common scenario in the railway system, and its channel characteristics are still to be studied. In this paper, radio wave propagation in a server room at 2.1 GHz is predicted using the ray-tracing method, and channel characteristics analysis is conducted through the information acquired from the channel model and rays. Electromagnetic parameters of material are calibrated based on the limited measurement to ensure the validity of the model. Different configurations of the 5G-R indoor scenario simulation can refer to this method, which greatly reduces the equipment, time, and human effort required for measurement.

The speed of train in a tunnel is closely related to tunnel size, and the size of tunnel has a great influence on the channel characteristics of wireless communication. Facing the demand of increasing train speed, it is important to choose a reasonable tunnel radius. This paper studies the effect of arch tunnel radius on the performance of MIMO wireless system in 3.5GHz and 28GHz tunnel scenarios. The channel of train communication under ultra-high speed is simulated based on ray-tracing approach. By analyzing the Root Mean Square delay spread and Doppler spread of signals under different arch tunnel, it is found that the delay spread and Doppler spread increase with the tunnel radius increment. Besides, the larger the tunnel radius, the greater the difference of the Delay spread between different frequency bands. These findings will have prolific values for the applications of MIMO channel based mobile communications in underground tunnels.

A metasurface-inspired antenna embedded in a metallic cavity is introduced here. It is expected to be integrated on fast moving platforms enduring harsh accelerations and shocks. The metasurface allows enlarging the antenna bandwidth that is intrinsically reduced for small antennas embedded in sub-wavelength metallic cavities. Circular polarization is achieved using two feed points connected the radiating aperture. The proposed antenna covers the E1, L1, B1 and G1 GNSS bands and exhibits a realized gain larger than 4.4 dBic, a half-power beamwidth of 112° and a cross-polarization level better than -20dB over almost the entire upper hemisphere. The numerical results are successfully validated by measurements.

In this paper a linearly polarized cylindrically conformal cavity-backed magnetoelectric (ME) antenna is presented. This antenna has a wideband behavior (S11 < -10 dB from 1.15 to 1.68 GHz) which covers all the GNSS bands and a small size of 75x75x40 mm3 (0.285x0.285x0.15 λ3 at lowest frequency). It also provides very steady radiation properties with gain of approximately 5 dBi and 3dB Beamwidth over 100° for all GNSS band and for both E and H planes of the antenna. A prototype was fabricated and a good agreement is found between measure and simulation.

Global navigation satellite systems (GNSS) positioning accuracy is nowadays important in many applications. The GNSS ideal antenna should exhibit an hemispheric coverage, in order to be able to receive signals at similar power levels for all positive elevations: this is not really the case with single antennas, exhibiting good coverage of near-zenith directions and then worse performance close to horizon. A conformal antenna for L1/L5 GNSS band is here presented. The antenna is a combination of multiple radiating elements, positioned on a conformal surface, such as to improve the coverage at low elevation angles, i.e. close to horizon. Simulations, manufacturing and measurements are shown in the paper.

A compact dual-band ring-slots with grounded-via integrated square-patch antenna is planned for circular/linear waves radiations. Four small unequal circular-ring-slots with grounded-via are integrated at the square patch corners for CP waves to reduce size of the antenna. These ring-slots with grounded-via offer compact antenna with CP radiation at the L-band. The antenna operates at the GNSS L1-band of 1.6 GHz with CP and 2.07 GHz with a LP for 5G New Radio applications. An integrated ring-slot with via acts as a CRLH structure, so that the four-ring-slots with via can miniaturize the antenna structure at 1.6 GHz. The confirmed outcomes of a prototype antenna with size of 0.32λo×0.32λo×0.0264λo are: the bandwidth of 5.6% (1.585GHz - 1.675GHz) at the L-band and 0.75% (2.04GHz-2.07GHz) at the S-band for 10dB return loss; 2.5% (1.59GHz-1.63GHz) at the L-band for 3dB axial ratio; peak gain of 4.9dBic at 1.62 GHz and 4.0dBi at 2.07 GHz.

To develop a compact distributed array for safe and robust automotive satellite navigation, considerable work on testing prototypes is in progress. Before scheduling resource-hungry outdoor tests, functionality and robustness of a Galileo-compatible compact distributed 4-element L-shaped array receiver has been tested against interference in a virtual environment at E5a frequency band. Such an array consisting of compact quarter wavelength sub-arrays distributed over many wavelengths, fed with a decoupling network, mounted in side mirrors of a mock-up car was measured and evaluated with and without a jammer. The effects of automotive mounting location and robustness of the receiver against the jammer have been analyzed in terms of measured radiation patterns and achieved carrier-to-noise-density ratio of the received satellite signals.

This paper presents a stacked patch antenna optimized to operate over the down- and uplink Ka-band for Deep Space applications. The design of the antenna is performed with a numerical optimization, to control the bandwidth and the impedance matching. A bandwidth of 5.53@33.185 GHz has been obtained, with a gain around 8 dB. On this design, a multiphysics thermal and mechanical analysis is performed to verify the operational stability of the optimized antenna, mounted on a 1U CubeSat satellite. The analysis verified that the antenna temperature patterns can affect the antenna matching, but it still allows correct operation in the [-100◦C,100◦C] temperature range. Moreover, the stress analysis reports a level of mechanical deformation which does not compromise the use and functioning of the proposed stacked geometry in a Low Earth Orbit space mission.

The development of devices for In-Situ Resource Utilization (ISRU) of the lunar surface powder (regolith) by means of microwaves needs regolith simulants with electromagnetic properties similar to the lunar regolith. Electromagnetic properties of EAC-1A and JSC-2A simulants had never been measured before. This document deals with the measurement of complex permittivity, complex permeability, and tangent loss of the aforementioned regolith simulants at ambient temperature from 400 MHz to 20 GHz. The obtained results will be applicable for comparing the measured values of EAC-1A and JSC-2A among them and with other previously measured simulants and real samples. The measurements were carried out applying two different non-resonant techniques. The DAK and EpsiMu kits were used to carry out the measurements according to the Open-Ended Coaxial Probe (OECP) and Transmission Line Methods.

In this paper, a wideband SU-8-based stacked meshed patch antenna is designed for integration with solar cells in CubeSats. The bottom meshed patch antenna is placed on glass substrate Corning 7070, and a thick layer of SU-8 negative photoresist serves as the upper patch substrate. The proposed antenna achieves a balanced compromise between the weight, robustness, transparency, and performance. The antenna bandwidth is 4.3%, from 2.376 GHz to 2.483 GHz, and the maximum gain in the entire frequency range is 5.3 dBi.

Performance verification of low gain antennas on small space platforms are challenging at frequencies below 400MHz, also owing to limitations in the anechoic environment. Spherical near-field measurement techniques are often applied in such cases, enabling different echo-reduction schemes to compensate for the non-ideal test environment. Uncertainties due to chamber reflections are also reduced with a directive probe but electrically larger probes are impractical at very low frequencies because of the resulting physical dimensions. A virtual probe, synthesized from an array of smaller probes, with limited wall illumination has been developed to reduce this error. The concept has been developed for measurements in the ESA/ESTEC HERTZ testing facility of the HERA-JUVENTAS mission with a 50-70 MHz dipole antenna mounted on a CubeSat. In this paper, we present the concept, feasibility and verification by measurements on a 10:1 scaled representation of the CubeSat scenario and the HERTZ facility.

During 2019-2022, ESA and EurAAP are conducting an antenna measurement facility comparison campaign involving 12 European institutions with a total of 13 spherical near-field and compact range measurement facilities. The employed reference antenna is the DTU-ESA mm-VAST antenna in three operational configurations at 19.76 GHz, 37.80 GHz, and 48.16 GHz, respectively. This paper documents the campaign background and organization as well as the first part of its execution. The comparison results will be published separately; this paper includes measurement results from DTU.

This work introduces a penalty-based regularisation to optimise the geometric parameters of a periodic frequency selective surface. A multi-layer bandpass filter with an equivalent circuit is used to illustrate the benefits of the approach for wide band applications. The proposed regularisation is obtained by convolving the frequency response and the desired thresholds before measuring the infraction. We apply bayesian optimisation on the unconstrained optimisation problem and assess the performance of the strategy by the number of objective function evaluations. A faster convergence and better robustness in the initial design of experiment is observed with the regularisation.

A semidefinite relaxation-based optimization framework originally developed for wireless power transfer systems in the near-field is adapted to maximize the antenna gain of reactively loaded antenna arrays in the far-field while simultaneously limiting the backlobe and sidelobe levels. The method is applied to a five-element linear dipole array and is successfully verified by simulation and measurements. The presented framework can be used for other types of loaded antennas as well as for geometrical optimization of dipole arrays.

The field of Computational Electromagnetics (CEM) consists of several techniques used to solve the electromagnetic (EM) response of arbitrarily shaped conducting objects. Selecting the most efficient and accurate solver usually requires extensive user experience and depends on the geometry and setup of the problem. This work aims to simplify this process by using machine learning models to predict whether a given solver would be sufficiently accurate before simulation. The hybrid Method of Moments and Physical Optics technique (MoM-PO) is considered in this investigation. It is found that predicting the accuracy of the MoM-PO when calculating the far field, near field and surface currents is in fact possible with F1-scores of 98.23, 97.61 and 92.26, respectively. Classification models such as Logistic Regression, Decision Trees and Artificial Neural Networks are considered.

The existent technique for shape optimization based on exact reanalysis of method-of-moments models is extended by symmetry operators. Their application is twofold: to prescribe a given symmetry and accelerate the optimization by reducing the number of unknowns, or to penalize unsymmetrical shapes, constraining thus the regularity and simplifying potential manufacturing.

This paper proposes a method for generation of Maxwellian far-field power patterns, to be used as input for a variety of electromagnetic inversion algorithms. Typically inversion source and scattering algorithms require a desired power pattern to reconstruct equivalent currents and/or material properties, but it is more common for the designer to provide only far-field pattern specifications such as beam directions, null directions, or half-power beamwidth. By using a method that represents an aperture antenna with a grid of infinitesimal dipoles, a set of training data is created consisting of current distributions (with varying phase and amplitude) and their corresponding power patterns as well as power pattern specifications. An encoder-only transformer neural-network model is then trained to recreate the full power pattern given only the specifications.

Digital coding representation of metamaterials makes it possible to realize intelligent designs of metamaterials using machine learning algorithms. Recently, there have been some works that have successfully designed the S-parameters of coding metamaterials with the machine learning techniques. However, wide-band reflection phases are much more difficult to design because of the periodicity of phase representation. Here, a machine learning method is proposed to automatically design anisotropic digital coding metamaterials with desired wide-band reflection phase responses (8-12GHz) under both TE and TM polarizations. Meanwhile, a deep learning method is presented to predict the phase curves in real time, in which the phase curves are creatively represented by their sine and cosine curves. A binary-particle-swarm optimization method is then introduced, cooperating with the deep learning prediction module to design the coding metamaterials in seconds, and the testing results show a state-of-art fitness of anisotropic wide-band phase responses.

This paper reviews the recent advances in artificial neural networks (ANN) for electromagnetic (EM) parameterized modeling and optimization. As an advanced ANN-based EM parameterized modeling and optimization technique, the neuro-transfer function (neuro-TF) is discussed further in this paper. The trained neuro-TF parameterized models can be further used for EM design optimization with repetitive geometrical variations.

Machine learning enters the world of medical application and, in this paper, it joins microwave imaging technique for brain stroke classification. One of the main challenges in this application is the need of a large amount of data for the machine learning algorithm training that can be performed via measurements or simulations. In this work, we propose to make the algorithm training via simulations based on a linear integral operator that reduces by three orders of magnitude the data generation time with respect to standard full-wave simulations. This method is used here to train the multilayer perceptron algorithm. The data-set is organized in nine classes, related to the presence, the type and the position of the stroke within the brain. We verified that the algorithm metrics (accuracy, recall and precision) reach values close to 1 for each class.

One of the primary ways that deep learning has been applied to electromagnetics in recent years is for accelerating inverse design. We present one such method for designing metasurface supercells which are robust to structural erosion and dilation, a typical variety of nanofabrication error. A pair of deep neural networks are trained to high accuracy to predict diffraction efficiencies from a supercell mask, and then evaluated exhaustively to find tolerance bounds for freeform supercell designs.

This paper proposes an intelligent beamforming architecture to predict the mapping relationship between codes and three-dimensional patterns. First, the two-dimensional intelligent beamforming (IB) framework is proposed. Then, the one-dimensional intelligent beamforming to realize the fast calculation of P-C and C-P is presented. The IB includes: 1) Substrate integrate waveguide programmable metasurface and automatic measuring systems design, 2) fast prediction from codes to patterns, 3) real-time prediction from patterns to codes, and intelligent beamforming architecture. Finally, the proposed IB is validated by the measured results.

In this paper, an innovative microwave imaging approach that combines deep learning techniques and qualitative inversion methods is presented. In particular, the proposed approach is meant for imaging piece-wise homogeneous targets and aims at providing an augmented morphological reconstruction, which not only retrieves the shape of the targets, but also the spatial variations of the permittivity values. Such an information is not displayed by qualitative inversion methods; however it is efficiently encoded in the gradient of the unknown contrast. In particular in this paper, a physics-assisted deep learning technique, where domain knowledge is given in the inputs of a U-Net architecture, is developed. The domain knowledge is provided by the qualitative image of the unknown targets obtained using the orthogonality sampling method, thus allowing the architecture to provide, once trained, a fully automated and real-time prediction. An initial assessment for the approach with synthetic data is provided.

The solution of inverse scattering (IS) problems supported by artificial intelligence (AI) is addressed. An innovative solution strategy based on the System-by-Design (SbD) paradigm is proposed for the computationally-efficient exploitation of a global optimization strategy for minimizing the data mismatch cost function. Towards this end, a suitable selection, customization, and interconnection of SbD functional blocks is adopted. Moreover, the computationally-unaffordable repeated evaluation of each trial solution during the optimization is bypassed thanks to the exploitation of a digital twin (DT) based on the learning-by-examples (LBE) paradigm. An illustrative numerical example is shown to prove the effectiveness and computational efficiency of the proposed solution strategy when dealing with 2D free-space microwave imaging (MI) scenarios.

The usage of unmanned aerial vehicles (UAVs) as flying base stations (FBSs) for expanding coverage and assisting the terrestrial cellular networks constitutes a promising technology for 5G and beyond. The wide range of a flying base station's movement may stretch the boundaries of path loss at the receiver's site and induce the occurrence of extreme values. Thus, using machine learning techniques may help in accurate path loss modeling for this case. In this paper, we use a combination of the techniques of ensemble learning and oversampling to provide a satisfactory path loss model for FBSs.

Antennas and arrays are indispensable elements of wireless communication systems. The directional characteristics is one of the most attractive features of antenna arrays. This article takes up a case of array pattern synthesis, and adopts two contemporary and highly competitive Evolutionary Algorithms, named Nondominated Sorting Genetic Algorithm III (NSGA III), and Double Niched Evolution Strategy for solving Multimodal Multiobjective Problems (DN-MMOES). The results show the effectiveness of Evolutionary Algorithms for such problems.

A common limitation among many applications involving machine learning techniques is the availability of training data. In propagation modeling scenarios, measurement campaigns are usually undertaken for network planning decisions. However, this can be a challenging task, especially in electrically large environments. In these cases, simulation data generated by physics-based methods, such as ray tracing, can replace or augment the measured data. This paper provides a case study in a typical office environment, where both measured and simulated data are used to separately train two machine learning models. A hybrid model combines the predictions of these two models, to predict the signal levels at any location in the environment. In cases where the volume of measured data is insufficient, the hybrid model is shown to improve the accuracy of the overall predictions. It is also shown that a small number of measurements can improve the accuracy of a solver-trained model.

The aim of this work is to provide guidelines on the design of wideband flat lenses composed of artificial dielectric layers (ADLs). Planar lenses based on metasurfaces or resonant elements are typically narrowband, due to the phase wrapping over the period of 360 degrees that is strongly frequency dependent. On the contrary, true-time-delay (TTD) planar lenses can achieve large bandwidths. One convenient way to design wideband TTD lenses is by means of ADLs, which are periodic arrangements of sub-wavelength patches embedded in a host medium to increase its effective permittivity. Tradeoffs including bandwidth, focal ratio, lens diameter and thickness are discussed and related to the manufacturing constraints of artificial dielectrics, such as number of metal layers and smallest features realizable in printed circuit board technology. An example of design is also presented, for 70-140 GHz operation, with a lens diameter of 11 wavelengths at the highest frequency.

In this paper, single and double ridged waveguides with glide symmetry are analyzed. By the inclusion of holes with semi-circle base in the ridge of the waveguides, the phase constant of the ridged waveguide can be effectively tuned. The value of the holes radii provides a fine modification of the slope allowing to set the desired phase difference in ridged waveguides. In addition, the separation between consecutive holes has been studied showing that when the glide symmetry is not preserved in the unit cell, a stopband appears in the dispersion diagram. The mirror-symmetric configuration of the holes provides the stopband with the largest bandwidth for both single and double ridged waveguides.

To fulfill the need for low-loss, low-cost devices with continuously reconfigurable phase at millimeter-waves, a glide-symmetric substrate-integrated phase-shifter design is presented. It exploits both the contactless guiding properties of high-impedance metasurfaces, and the high refractive index variation of glide-symmetric waveguides. Mechanically moving the substrate-integrated layers yields a continuous phase change due to the effective refractive index variation. Glide symmetry reaches a larger index variation, reducing the length of the phase-shifter.

A microstrip-technology three-way waveguide has been conceived to exhibit exceptional modal degeneracy in the presence of periodic gain and radiation losses. A third order exceptional point of degeneracy (EPD) is obtained in the dispersion relation of a periodic structure consisting of three coupled microstrip waveguides satisfying parity-time (PT) glide-symmetry. A third order EPD exists when three Floquet-Bloch eigenmodes of a periodic structure coalesce at a single frequency, in eigenvalue and polarization state. PT-glide-symmetry is achieved in the proposed structure using periodically spaced lumped (radiation) loss and gain elements. Such a degeneracy can be utilized in the design of devices such as radiating arrays with distributed amplifiers, arrays of oscillators, and sensors.

In this work, we design a planar half-Luneburg lens antenna. The gradient of refractive index is realized using a dielectric slab periodically loaded with air-cavities of varying size. The cavities are glide-symmetrically arranged. It is demonstrated that by introducing glide symmetry, the bandwidth and range of realizable refractive indices are increased compared to a non-glide-symmetric structure. The lens antenna operates from 22 to 32 GHz and can scan its directive beam over a 50 degree range in the H-plane. The side lobe level in this scan range is lower than -10 dB throughout the band. The lens can be produced using additive manufacturing.

This paper reports the application of higher symmetries to the design of a Reflecting Luneburg Lens (RLL) with broadband response. RLLs consist of two circular parallel plate waveguides (PPWs) vertically stacked. The bottom PPW is filled with an azimuthally symmetric graded index (GRIN) medium. Owing to this GRIN medium, the wave launched by a primary feed in the bottom PPW is collimated in the top one, so that a plane wave with a different propagation direction is generated for any azimuthal position of the source. In this work, the GRIN medium in the bottom PPW is implemented by higher symmetry unit-cells consisting of metallic inclusions. This type of unit-cell achieves the required equivalent refractive index profile with reduced frequency dispersion, thus increasing the operational bandwidth of the lens. The proposed architecture constitutes a low-profile beam-forming solution that also provides complete azimuthal scanning in a wide frequency range.

A new type of microwave oscillator arrays based on topological metamaterials is presented. The arrays are built upon a new form of microwave topological insulators consisting of a dual lattice of transmission lines. The proposed structures support extended oscillation modes with remarkable stability against discontinuities and disorder, and arbitrary phase profiles. A comparison with oscillator arrays based on conventional transmission lines is presented, demonstrating a clear superiority for the topological ones. The presented structures create a new direction in the design of microwave oscillator arrays over large areas for applications in phased antenna arrays and time-modulated nonreciprocal devices.

Spatially-discrete traveling-wave modulation (SDTWM) is a form of space-time modulation, in which staggered time-modulated signals are applied to a discrete array of unit cells, referred to as stixels: space-time pixels. SDTWM has been shown to support electromagnetic functionalities like amplification, frequency conversion, beam steering and nonreciprocity. Modeling SDTWM using standard techniques and commercial solvers is complicated by the fact that a single spatial period may include a large number of time-varying stixels. In this paper, a boundary condition, known as the interpath relation is shown to dramatically simplify the analysis of SDTWM structures. The interpath relation arises from the higher-order space-time symmetry inherent to SDTWM. By invoking this symmetry, the field solution throughout space can be determined from the field solution in a single stixel. The application of the interpath relation for computing the dispersion and scattering response of two representative SDTWM structures is reported.

Absorbers play a pivotal role in protecting sensitive electronic devices from unwanted signals. In this work, we present new types of absorbers based on structures that are invariant under the Parity Time-reversal Duality (PTD) transformation. Such structures produce zero backscattering under the illumination of a plane wave at normal incidence. This reflectionless feature is exploited to design wideband absorbers. Numerical results of the proposed absorbers are also discussed.

Efficient and accurate indoor radio propagation modeling tools are essential for the design and operation of wireless communication systems. Lately, several attempts to combine radio propagation solvers with machine learning (ML) have been made. In this paper, motivated by the recent advances in the area of computer vision, we present a new ML propagation model using convolutional encoder-decoders. Specifically, we couple a ray-tracing simulator with either a U-Net or an SDU-Net, showing that the use of atrous convolutions utilized in SDU-Net can enhance significantly the performance of an ML propagation model. The proposed data-driven framework, called DeepRay, can be trained to predict the received signal strength in a given indoor environment. More importantly, once trained over multiple input geometries, DeepRay can be employed to directly predict the signal level for unknown indoor environments. We demonstrate this approach in various indoor environments using long range (LoRa) devices operating at 868 MHz.

We report a method for predicting fading distribution of path loss using GRU, which is a RNN as deep learning. The training data and validation data use path loss measured in Yokosuka City, Kanagawa Prefecture, Japan, and the measurement frequency is 4.7 GHz. By using 100 points of fast fading data about every 0.1 seconds, the median data of path loss and the K factor of Nakagami-Rice distribution after 1 second were predicted. The median data and the K factor are derived using the fast fading data of 100 points (about 10 seconds). According to the prediction method using GRU, the RMSE for the validation data is about 1.7 dB for the median path loss and about 0.5 dB for the K factor. The prediction accuracy was improved by 0.9 and 0.1 dB compared with the case of using latest observed values.

A testbed that emulates wireless communication in a virtual space is needed to efficiently validate a new wireless communication system in large-scale and various environments. For realistic wireless emulation, it is necessary to simulate the radio propagation characteristics site-specifically and accurately. Some modeling methods based on machine learning using map data have been proposed. However, using a single modeling approach in various propagation environments may result in lower accuracy. Also, single modeling in the extensive area has issues of computational cost and model-tuning efficiency. This paper proposes a method for clustering map data and modeling for each cluster using machine learning. This method optimizes the modeling area corresponding to the geographical features and improves accuracy and computational efficiency. The evaluation results using measurement data showed that the proposed method improved the accuracy and increased the speed by approximately 30%.

Within the Marine Surface Boundary Layer, evaporation ducting greatly affects the radar performances. The vertical refractivity profiles are classically computed by bulk models and these profiles can be fitted, with a very good accuracy, by analytical expressions involving four parameters to be determined. With machine learning techniques and particularly a decision tree regressor, we directly obtained these parameters from the physical bulk inputs. The resulting refractivity profiles are generally very closed to the original ones and in terms of propagation results we obtained mean errors around 1 dB by computing the propagation factor for classical radar scenarios.

Radio signals propagating indoors will produce positive bias due to non-line-of-sight (NLOS) conditions, which seriously affects the accuracy of positioning. In order to distinguish between line-of-sight (LOS) and NLOS conditions, we combined the kernel principal component analysis method (KPCA), genetic algorithm (GA) and support vector machine (SVM) classification algorithm to propose a NLOS detection method based on KPCA-GA-SVM. A channel measurement campaign at frequency band from 2.4 GHz to 5.4 GHz was carried out in an indoor environment, and the proposed algorithm was evaluated through the measurement data. The results show that the KPCA-GA-SVM algorithm has a high accuracy for LOS and NLOS detection, and eliminates the correlation between different features, thus shortening the running speed of the algorithm.

We report on progress towards a sparse 4x1 scanning lens phased array at W-band (75-110 GHz) capable of beam steering a directive (>30 dBi) beam towards 15deg with sidelobe levels below -10dB. The lens array relies on a combination of mechanical and electrical phase-shifting to steer the beams. These concepts have been demonstrated separately, but we are working towards the first demonstration of the concept with mechanical and electrical phase shifting. The lens feed achieves high aperture efficiency illumination of the lenses by suppressing the spurious TM0-mode over a wide bandwidth with annular corrugations in a groundplane. We have fabricated a 4x1 W-band array prototype. Preliminary measurements of a single lens are in good agreement with simulations. We present preliminary measurements from a W-band electrical phase-shifting setup using low-frequency IQ-mixers that will allow 20deg scanning of the array. More measurement results from the array will be presented at the conference.

This work introduces a new core-shell lens antenna based on low-cost plastic materials and a leaky-wave in-packaged antenna at 150GHz. The lens antenna is made of an electrically small core lens made of a dense material to enhance the radiation from the in-packaged antenna, plus an electrically large shell lens made of a low loss dielectric material. The proposed lens antenna presents good quality patterns with aperture efficiencies above 80% over a bandwidth of 20%. A single layer feeding network using a coplanar waveguide line for connection to a 150GHz chipset is also discussed. Good impedance matching is achieved over a bandwidth of 25%.

Various aspects of implementing a gradient refractive index distribution using 3D printing are considered. These approaches are applied to two types of lens design: cylindrical Luneburg lens and thick flat lens. Based on simulated and measured results the main constraints for the lens design using additive manufacturing are defined.

New radar architectures employ multiple transmitters and receivers to enhance their performance, combining wide and narrow beams to improve the spatial resolution. In this contribution, two antenna system configurations based on stacked geodesic lenses are compared. These lenses are fully-metallic parallel plate waveguides that present very low transmission losses in the millimetre-wave band. Narrow beams are generated by a 15-port Luneburg-Rinehart lens with a scanning span of 100º and 23.4 dB gain at 77 GHz. For wide beams, two alternatives are proposed. One alternative is a 3-port defocused lens antenna with a scanning angle of 100º and 14.5 dBi gain. The second proposal is a 12-port Luneburg-Rinehart lens fed with 1-to-4 power dividers forming a 3-port antenna with a scanning span of 91 and 16.2 dBi gain.

This paper presents a novel quasi-optical power distribution technique based on a transmit lens array that allows achieving an efficient multi-pixel LO power distribution for submillimeter-wave instruments. This method can distribute the power from one antenna to a multi-pixel lens array in a hexagonal configuration with a power coupling efficiency of nearly 60%. To maximize this coupling, we synthesize a top-hat radiation pattern using multi-mode leaky-wave feeds that feed silicon elliptical lenses. Moreover, the proposed transmit array architecture could be operated in a coherent mode for applications requiring beam steering of highly directive beams. We will present a prototype based on a transmit array of 7 pixels at 450-650 GHz with preliminary measurements showing a good agreement with simulations.

Characteristic Mode Analysis (CMA) is exploited for the design of a metasurface (MS) able to convert a linearly polarized field into a circularly polarized one. A MS is adopted for the design of an antenna aiming to operate in the whole X-band for satellite communications (7.25 GHz-7.75 GHz, 7.9 GHz-8.4 GHz). CMA results provide useful insight for properly tuning the unit cell of the finite MS, which is based on a loop element. A comparison between two different solutions is addressed and an excitation strategy for stimulating the desired characteristic modes is envisioned.

Characteristic mode analysis (CMA) of perfectly electrically conducting (PEC) bodies is very useful for many applications. To develop a robust CMA tool for efficient modeling of large-scale PEC objects, several technical aspects have been considered to systematically implement the tool. Their resultant generalized eigenvalue equations are solved using implicitly restarted Arnoldi method (IRAM) accelerated by multilevel fast multipole algorithm (MLFMA). A sparse approximate inverse (SAI) preconditioner is employed to improve the convergence of the iterative solution process. As an important application of the CMA tool, fast reconstruction of scattering cross-section of complex PEC objects has also been developed for obtaining electromagnetic scattering data.

Characteristic mode analysis (CMA) is very useful for the design of antennas. Antenna performance can be optimized by characteristic mode (CM) manipulation. However, the mechanism of mode manipulation using dielectric materials has not been well revealed. In this paper, the equivalent circuit model (ECM) is used to predict the modal admittance (MA) of the antenna over a broad bandwidth. Parallel-connected lumped components can be used to modify the ECM to reflect the influence of dielectric material on the MA.

Notable sparsity, symmetry, and tracking properties of characteristic modes on periodic systems are discussed. A set of example calculations demonstrate sparsity in reconstructing the reflection tensor from characteristic modes, as well as the multidimensional parameterization of modal quantities infrequency and scan angle.

An insightful approach to single-element beamforming is presented. In order to enhance the understanding of single-element beamforming, a change of basis is used to connect the characteristic modes of a single element to array theory. For the analyzed patch antenna, this allows not only the derivation of new explicit relationships for the excitation, but also enables the use of the array factor and other valuable tools from array theory.

Guided electromagnetic waves have been proposed recently as a novel technique for surface damage detection in metallic structural components. One limiting factor is frequency dispersion, which causes an emitted pulse to spread out in space and time as the wave propagates. This paper presents a dispersion compensation technique, originally introduced in the field of guided ultrasonic waves, that significantly improves localization accuracy by nonlinear mapping from time to distance domain exploiting a-priori knowledge about the dispersion characteristics. The method compresses the dispersed signal to its original shape. An application of the technique is presented in this paper considering damage localization in a complex WR28 waveguide covering the frequency band from 20-40 GHz. Therefore, the fundamental dispersion relationships for phase and group velocity have been derived. The results show a strong compression of the waveforms through dispersion compensation leading to an improved localization with an error of less than 1%.

In this paper, we propose a comprehensive low-power and low-cost Angle of Arrival (AoA) estimation system. The proposed system consists of a hardware architecture and an AoA estimation algorithm. The proposed hardware captures the phase values of the received signal and transmits them to the nearest LoRaWAN gateway. In the cloud, an AoA estimation algorithm will be performed, and the AoA of the received signal will be estimated. The proposed hardware is generic, and it can estimate the AoA of any received signal that is operating at a frequency below 2.7GHz. However, we have validated its performance with LoRa signals that are operating at the 868 MHz frequency band. The experimental validation, which has been conducted in a controlled environment, reveals that the proposed system can estimate the AoA of the received signals from various azimuth angles with a median and maximum estimation errors of 4 and 14 degrees, respectively.

Two receiver structures of phase modulated FMCW signals with low ADC sampling requirement are investigated, namely the matched filter of the dechirped signal and the group delay filter approach. The sensing performance of the investigated receiver strategies are analyzed in application to BPSK modulated chirp. Numerical simulations demonstrate that both techniques provide comparable performance for low to moderate bandwidth of the modulation signal. Matched filter outperforms the group delay receiver for the modulation waveform with large bandwidth, hence with the price of larger computational complexity.

Recent studies revealed that scattering calculations at weather radar frequencies using individual drop shapes result in better agreement between simulated and measured polarimetric weather radar parameters, than if established rotational symmetric shape models are used. In the present work, thousands of individual rain drops that were detected with a 2D Video Disdrometer during a tropical storm, were reconstructed and their individual radar cross sections (RCS) were calculated by automatizing a commercial EM solver software. The calculations were carried out at the common weather radar frequencies at 2.8 GHz and 5.625 GHz, both for horizontal and vertical polarization. It is evaluated to what extend the RCS can differ for drops with an equal volume, it is discussed how the scattering parameters of individual drops scale within S- and C-band frequencies, and it is shown for one sample drop what effect the modelling granularity has on determined radar cross section values.

Harmonic transponders differ from linear transponders by offering higher clutter mitigation and especially when the transponders are placed on highly reflective items or present in reflective environments. This paper exploits the inherent non-linearity in order to clearly sense and localize these transponders. The employed transponder is completely planar with a small footprint of 2 cm (\times ) 3 cm. Furthermore, the transponder consists of two bowtie dipoles that are directly matched to the harmonic generation element at a fundamental 2.45 GHz frequency and also at the corresponding second harmonic 4.9 GHz frequency. In this paper, the inherent non-linearity sensing is exploited with synthetic aperture radar (SAR) in a highly cluttered environment. The proposed method benefits by providing precise information along range and cross-range directions.

The current beamforming strategy for the SKA-Low prototype station AAVS2 is the standard geometric-based array factor approach, as used in traditional array analysis and design. This method is simple, but because it ignores both mutual coupling and the inter-element variation in radiation patterns, it becomes progressively less reliable as the operating frequency decreases and the scan angle off broadside (zenith) increases. In this paper, the maximum directivity beamformer is applied to a computational electromagnetic simulation of an AAVS2 station. This formulation leverages the embedded element patterns and the array mutual coupling matrix. This permits considerably improved beam steering, in particular at the bottom end of the SKA-Low band. The computational cost of the method is also discussed.

A newly developed phased array concept for LOFAR 2.0 radio telescope makes simultaneous Space weather and Radio astronomy observations possible

The design of an all-metal quadruple-ridged flared horn (QRFH) feed antenna for the ngVLA optics is presented. The feed is required to operate over the 1.2 GHz - 3.5 GHz frequency band with an optimization goal of maximizing the receiving sensitivity (Ae/Tsys) at an elevation angle of 45° and minimizing the fundamental waveguide mode reflection coefficient over the specified frequency band. The initial optimization was done on an analytically defined profile for both the horn and ridges, which provided a good starting point for optimizing horns with spline-defined profiles. In the final optimizations, the maximum ridge length was constrained to be about three-quarters of the total horn's length to allow for the addition of thermal and vacuum breaks. The final design has an average sensitivity of 13.4 m2/K over frequency and tipping angles.

Orthomode transducers form an integral part of any receiver system, especially for high sensitivity, wideband applications such as reflector feed antennas for radio astronomy. This paper presents an improvement on the quadruple-ridged OMT that has formed the basis for many high performance reflector feeds systems. The improvement relies on the freedom offered by SLM 3D-printing to design quadruple-ridged waveguides with a wider single mode bandwidth than conventional square/circular ridged waveguides. A prototype quad-ridged OMT is designed and manufactured to operate over 3.5 - 12.3 GHz, the ngVLA Band 2. The manufacturing and measurement of the prototype is discussed in detail with recommendations for future designs. The basic design of the proposed OMT can be customised to attain good performance over more than a decade bandwidth, or used as a basis for high performance narrowband applications.

A complete reflector antenna architecture solution has been developed for Cryorad mission operating from 400 MHz to 2 GHz. This paper analyzes the antenna feed requirements and proposes an array feed solution comprised of two different frequency feeds. The design and analysis of one the proposed conical logarithmic spiral feed have been carried out. More than 10 dB of directivity radiation pattern from 900 MHz up to 2 GHz with a directivity stability of ±0.5dB using only a 130 mm diameter feed has been developed. Single circular polarization is achieved with an axial ratio under 1 dB within the complete operating band. The proposed feed is ideal for use in satellite due to its reduced size and mass.

Literature on antenna gain calibration using extrapolation method has mostly focused on antennas with moderate to high gains where chamber reflections are relatively small. The traditional technique to remove antenna-to-antenna multipath reflections is to apply a moving average over the antenna response before a polynomial fit is applied. For low gain antennas, multipath reflections from surroundings can be much more pronounced. The moving average approach may not provide enough echo suppression. In this study, we investigate two additional techniques for removing the multipath reflections. The first technique is to apply time domain gating. Another method is to use angular spectrum filtering. At each frequency, the antenna response is expanded to k-space, where a filter can be applied to retain the response from the direct path direction only. The three techniques are compared using a set of measured data of broadband dipoles in an anechoic chamber.

Recently the author presented two papers on the use of full wave numerical methods for the prediction of anechoic chamber performance. In the first paper [1] the author argued that full wave analysis while accurate is still dependent on the accuracy of the input parameters, one of which may be the material properties of the RF absorber. On the second paper [2] presented the author stated that full wave analysis should be reserved to evaluating the potential effects of defective absorber of location of lights in different areas of the range. In this paper the author compares the full wave analysis of a taper anechoic range with the measured performance of the implementation of said tapered range.

A possible spatial support for equivalent sources accounting for echoic distortions in measurement scenarios with a moving AUT and a fixed probe location is discussed. In a heuristic argument, an equivalent scenario is introduced, where an unphysical ghost AUT, which is identical to the original AUT except for a constant scaling factor, accounts for the no longer present echo fields. A toroidal ghost source region around the moving AUT is, thus, identified and confirmed by a simulated measurement campaign. In the simulated measurements, the fields from reconstructed sources in the proposed region usually deviate by less than -40 dB compared to the fields from reconstructed sources on a large sphere or an untruncated mode expansion. The newly found spatial interpretation of the additional echo sources adds valuable insights to the mechanisms of echo suppression techniques based on modal expansions or surface current reconstruction.

The physical and electrical size of the parabolic reflector largely determines the usable size of the CATR QZ, with the reflector edge treatment being hugely influential in terms of determining the overall quality and uniformity of the collimated, pseudo plane wave. Recently, it has been demonstrated that modern powerful digital computational simulation technology in combination with evolutionary optimization strategies can be successfully harnessed to optimize the serrated edge treatment of an offset-fed CATR as part of the design process. In this paper, a further enhancement is presented in which the evolutionary computing technique is applied to the more geometrically complex blended rolled edge (BRE) treatment of a rectangular CATR reflector. Results of the validation of this novel technique are presented together with optimized QZ performance that highlight the successful use of this design procedure.

The basic idea to validate an anechoic chamber from 30 MHz to 1000 MHz is discussed in brief, and then focus on the correction factor in normalized site attenuation method. A calculable biconical antenna is provided and experimentally verified. The difference of antenna factor between measurements and calculation is less than 0.2 dB. The correction factor of NSA is provided for 5 m range measurements. Finally, a measurement uncertainty example is shown for validating the semi-anechoic chamber with reference site method.