An analytic theory has been developed for the scattering of electromagnetic plane wave from a perfect electromagnetic conducting (PEMC) cylindrical object coated with a general bi-isotropic (BI) material. The proposed problem has been solved using cylindrical vector wave function expansion approach along with the application of tangential boundary conditions. Analytic expressions of the scattering coefficients have been derived in their simplest forms. It is seen that by proper selection of admittance of PEMC core, electromagnetic parameters of BI coating, and coating thickness, one can optimize the scattering characteristics for specific applications. It is shown that the specific types of BI and strong chiral-coated PEMC cylinders having certain coating thicknesses can be used to significantly enhance the co-polarized forward scattering while keeping the cross-polarized forward scattering very small. Such types of enhanced co-polarized forward scattering are preferred in point-to-point communication. Some interesting features have been discussed where co-polarized and cross-polarized backscattering may be suppressed, which find applications in radar engineering problems and stealth technology.

This paper presents a pattern reconfigurable antenna that accomplishes wideband and multibeam characteristics. The antenna design comprises a cross-slot radiator as the primary element and reconfigurable partially reflecting surface (PRS) layer placed above and below the cross-slot radiator. This configuration allows the antenna to adapt its radiation patterns effectively. The choice of the cross-slot radiator is based on its capability to offer wideband characteristics. The PRS layer consists of a precisely arranged array of 4×4 unit cells, incorporating PIN diodes into both the upper and lower PRS layers. The direction of radiation pattern can be changed by altering operating states of the PIN diodes on the PRS layer. The antenna operates in three distinct states, each exhibiting a unique radiation pattern. The antenna produces broadside, backward, and bidirectional radiation patterns. It demonstrates effective pattern reconfigurability across the frequency range of 3.10–3.86 GHz (21.71%), with a peak gain of 9.60 dBi. The simulated and measured results of the antenna are found to be in good agreement.

With the increasing demand for smarter antenna design in advanced technology applications, well-designed antennas have been an important factor in enhancing system performance. Most traditional antenna design requires multiple iterations and extensive testing to produce a final product. Machine learning (ML) algorithms have been used as an alternative to predict the optimal design parameters, but the outcome depends highly on the ML model efficiency. With recent development in machine learning algorithms and the availability of data for antenna design, we investigated different machine learning algorithms for optimizing the output strength of three basic antennae by analyzing the signal strength of the antenna for various antenna parameters. Different regression-based ML models were used to learn the behaviors and efficiency of three different antennas and to predict the output strength (S11) for different ranges of frequencies. The experiment compared and analyzed these ML regression algorithms for three different antennas: shot antenna, patch antenna, and bowtie antenna. In addition, the paper also provides comparison of ensemble ML models for performance analysis using the best three ML algorithms from the preliminary study. This study optimizes antenna parameters and quicker and smarter antenna design procedure using ML algorithms as compared to traditional design methods.

This paper introduces a method to realize beam switching by using a substrate-integrated waveguide (SIW) Butler matrix combined with a slot array antenna. The Butler matrix consists of two hybrid couplers, two crossovers, two −45-degree phase shifters, and two 0-degree phase shifters. The slot array antenna is a 4 × 2 array. The operating frequency band of the slot array antenna, where the reflection coefficient is below −10 dB, is 26.5–31.5 GHz. The measured beamforming angles from input port 1 to input Port 4 of the Butler matrix are +46, −16, +15, and −50°, respectively. The corresponding antenna gains from input Port 1 to input Port 4 are 11.57 dB, 14.284 dB, 10.94 dB, and 12.864 dB, respectively. The dimensions of the Butler matrix and the slot array antenna are 56.8 mm × 21.2 mm × 0.254 mm. The dimensions of the SIW transmission channels between the Butler matrix and input Ports 1– 4 are 16.9 mm × 34 mm × 0.254 mm.

A compact microstrip eight-channel diplexer based on quad-mode stepped impedance resonator (QMSIR) is proposed in this paper. The proposed diplexer is composed by two second-order quad-band bandpass filters (BPFs) and common-port distributed coupling matching circuit. Each quad-band BPF is formed by two coupled-QMSIRs controlling the passband characteristics. By introducing multiple coupling paths between input and output ports, the isolation between the eight channels is performed. For demonstration, an eight-channel diplexer based on QMSIR is designed and fabricated with microstrip technology. The use of the QMSIR can lead to significant size reduction for the multiplexer, this is because the required resonator number is reduced. As a result, the diplexer occupies a compact size of 0.083λ2, which is smaller than most of the eight-channel diplexers that have been proposed. And the 3 dB fractional bandwidth is 97% (2.5–7.2 GHz). Measurement results correlate well with the simulated predictions, showing that a good isolation of better than 20 dB and upper stopband of better than 10 dB.

In this paper, a compact two-element reconfigurable multiple-input multiple-output (MIMO) antenna for 5G new radio sub-6 GHz is presented and discussed. The proposed MIMO antenna has four frequency operating modes: a wideband operating mode (2.41–6 GHz), a wideband operating mode with a notching band at 3.5 GHz (3.2–3.66 GHz), a low-pass filter mode that filters the higher frequencies with a wide operating band from 2.41 GHz to 4.7 GHz, and a dual-band mode with two operating narrow bands (2.41–3.16 GHz and 3.64–4.7 GHz). To improve the isolation over the entire operating band, a strip line connecting the two ground planes of the two antenna elements has been used. To validate the proposed approach, different prototypes have been fabricated and measured. The simulation results are in good agreement with the measurement results. The proposed antenna has good MIMO diversity performance with a maximum gain of 4.64 dBi. The minimum isolation is 18 dB for the four operating modes, while a measured envelope correlation coefficient of less than 0.008 is achieved. The diversity gain is near 10 dB for various operating modes. The antenna is suitable for cognitive radio and 5G sub-6 GHz applications.

We present the design for a thin planar microwave absorber depicting near unity absorption over a wide bandwidth. The absorber consists of a single layer of resistive frequency selective surface inkjet printed over a paper substrate and suspended over a grounded foam. We have been able to achieve 99.99% absorption of normally incident radiations from 9.7 to 11.74 GHz at an extremely low level of −40 dB absorption bandwidth. The proposed absorber is thin (0.22λ0 at the center frequency), polarization-insensitive, and presents −10, −20, −30, and −40 dB fractional bandwidths as 89.83%, 55.41%, 33.30%, and 19.03%, respectively. It is worth mentioning that the design of an absorber with such steep slopes is highly stringent and requires special attention. Finally, we have experimentally demonstrated the perfect broadband absorption characteristics with a fabricated prototype.

This paper presents a method to design the response threshold (RT) of energy selective surface (ESS) based on series LC circuits (SLC_based_ESS). A simple SLC_based_ESS structure composed of metal strips and PIN diodes is used for demonstration. According to our research, the RT is rarely related to the geometry parameters of unit cells. By contrast, the RT could be designed by introducing auxiliary structures (ASs) to SLC_based_ESS arrays. With the AS, the induced currents on diodes are enhanced and thus RT is greatly reduced. Prototypes are fabricated and measured under different power levels. The results agree well with simulations, proving an effective design of RT by the proposed method.

Aiming at the problem that the covariance matrix includes the desired signal and the signal steer vector mismatches will degrade the beamforming performance, an effective robust adaptive beamforming (RAB) approach is presented in this paper based on a residual convolutional neural network (RAB-RCNN). In the presented method, the RAB-RCNN model is designed by introducing a residual unit, which can extract the deeper features from the signal sample covariance matrix. Residual noise elimination and interferences power estimation are utilized to reconstruct the desired signal covariance matrix, and correct the mismatched steering vector (SV) by the eigenvalue decomposition of the reconstructed desired signal covariance matrix. The projection method is utilized to redesign the signal interference-plus-noise covariance matrix. Furthermore, the beamforming weight vector is calculated with the two parameters obtained before and used as the label of the RAB-RCNN model, The trained model can rapidly and precisely output the predicted beamforming weight vector without complex matrix operations, including the matrix inversion of the signal covariance matrix, so that the calculation time can be reduced for beamforming. Simulations demonstrate the robustness of the presented approach against SV mismatches due to the direction-of-arrival estimation error, sensor position error, and local scattering interference.

Resonant Bessel-beam launchers (BBLs)are radiating devices constituted by a cylindrical metallic cavity with a partially reflecting sheet (PRS) on top. Millimeter-wave resonant BBLs typically exhibit transverse magnetic (TM) polarization due to the use of coaxial probes as feeders and homogenized metasurfaces as PRS. Launchers showing either a purely transverse electric (TE) or a hybrid (quasi-TE) polarization have recently been proposed for realizing wireless power transfer (WPT) links in the radiative near-field region at millimeter waves. The former are obtained by means of a radial slot array as a feeder and a homogenized metasurface as a PRS. The latter are obtained by using a loop antenna as a feeder and an annular strip grating in the homogenization limit as radiating aperture. In this work, based on an original semi-analytical model, such a metasurface is demonstrated to show a dichroic behavior. This interpretation explains the improvement in terms of polarization purity with respect to more nondichroic conventional homogenized metasurfaces. The behavior of the annular strip grating under a pure TM polarization is tested with a coaxial feeder, whereas its behavior under a pure TE polarization is tested by means of the radial slot array feeder. Results confirm the validity of the proposed analysis, which is finally exploited to evaluate the WPT performance.

This paper presents an optimization method for pattern synthesis of distorted phased array antenna with unsteady surface deformation considering the dynamic range ratio (DRR). In the synthesis approach, different array deformations under unsteady mechanical loads are considered, and the distorted distribution of array elements is calculated after solving the mechanical deformation model. Then, optimize the excitation coefficients of each array element including amplitude and phase with DRR control so as to recover a high-quality pattern from a deteriorated pattern caused by the unsteady deformations. The optimization objective is to minimize the peak sidelobe level, which is synthesized by using a gradient-based algorithm. The optimized excitations can be used as the initial excitation, and the corresponding phase excitations can be derived according to the different deformations.

This study presents the design and realization of a dual-port multiple-input–multiple-output (MIMO) filtering antenna system. The device shows good response in the frequency rage 1 (4.1 to 7.125 GHZ) frequency band, which handles most of the cellular mobile communication traffic. First, the single element ultra-wideband (UWB) filtenna is designed by combining a UWB antenna and a band-reject filter (BRF) where the antenna works in the frequency range from 1 to 11 GHz and the BRF is rejecting the frequency range of 3–3.42 GHz with 3.2 GHz as its resonant frequency. Finally, the proposed two-port MIMO filtenna combines two single element UWB filtennas in antiparallel manner which shows impedance bandwidth from 2.59 to 7.1 GHz with a band notch from 3 to 3.42 GHz. The structure is built on cost-efficient FR4 substrate (εr = 4.4, tanδ = 0.02) of dimensions 0.68${{\boldsymbol{\lambda }}_{\boldsymbol{c}}}$×0.27${{\boldsymbol{\lambda }}_{\boldsymbol{c}}}$×0.01${{\boldsymbol{\lambda }}_{\boldsymbol{c}}}$ (mm3), which is compact in size and utilizes a defected ground structure for further miniaturization. The proposed design is simulated using Ansys HFSS software, and after fabrication, it is measured, and the output shows good results for the proposed application. The designed antenna system is suitable for fifth-generation (5G) wideband systems.

In this article, an angle-independent wideband metamaterial microwave absorber (MMA) for C (4–8 GHz) and X (8–12 GHz) band frequency is presented. The unit cell of the proposed MMA consists of outer and inner structure associated with lumped resistors. The outer structure consists of rectangular split-ring resonator, whereas the inner structure consists of circular split-ring resonator. The structure is made up of three layers, in which top and bottom layers are made up of copper acting as a conducting material. The middle layer is made up of FR-4 acting as a dielectric substrate. The resonating structure at the top is designed in such a way that wideband absorption is achieved in the range from 6.11 to 13.52 GHz. The wideband absorption within the range approaches almost unity having a bandwidth of 7.41 GHz. Three different peaks are considered in the range of interest having maximum absorption of 0.94, 0.94, and 0.99 at frequencies of 6.76, 11.15, and 13.07 GHz, respectively. The structure is analyzed with respect to the effective parameters, i.e., effective permittivity (${\varepsilon _{{\textrm{eff}}}}$) and effective permeability (${\mu _{{\textrm{eff}}}}$), to prove that the structure acts as a metamaterial. Electric field and current distribution are plotted at three different peaks to prove the mechanism of wideband absorption. Normal and oblique incidence are plotted to determine that the structure is behaving as an angle independent. The simulated structure is fabricated on FR-4 substrate and measured inside an anechoic chamber. Finally, to prove the novelty of the work, the proposed structure is compared with the already reported MMA. The proposed MMA finds practical applications in radar cross section reduction, terrestrial communication, keyless entry system, space communication, radar, and baby monitor.

Basically, a 4 × 4 Butler matrix (BM) connected to an antenna array allows to have four beams, each oriented in a specific direction depending on the excitation port. In this paper, an almost continuously steerable beam system based on a conventional 4 × 4 BM with adjustable phase shift is presented and demonstrated. Here, varicap diodes are used instead of an additional phase shifter. Under different bias levels applied to the couplers throughout these varicap diodes, an output variable phase difference was obtained. A prototype of the proposed tunable BM integrated with an antenna array operating at 3.5 GHz was fabricated and tested. The experimental results show a good agreement with those simulated. A reflection and isolation coefficient better than −15 dB over the entire desired frequency band and an amplitude imbalance lower than ±1.5 dB were achieved. The measured radiating beam under different DC biasing can be oriented from ±6° to ±18° when port 1 or 4 is excited and oriented from ±32° to ±43° for ports 2 and 3.

In this article, a coupled line diplexer (operating at 2.4 GHz and 3.5 GHz) which can be used as single-band filter with tunable attenuation characteristics in the pass band has been designed. Multilayer graphene (MLG) pads are used to achieve tunable features in this circuit. The graphene pads are placed at each branch of the diplexer. Single-band tunable attenuation characteristics are achieved by applying bias to graphene pads placed at optimum locations on the filter. The proposed tunable coupled line attenuating diplexer is realized on FR-4 glass epoxy substrate of thickness 1.58 mm with a total size of 45 × 75 mm2. By varying the bias voltage (0 V –6 V) of MLG pads the resistance of graphene pad placed in the circuit gets decreases thereby attenuating/controlling the transmission power to the other port in the required band. In lower pass band (2.28–2.55 GHz) the signal is attenuated from 3 to 10.8 dB and in higher pass band (3.2–3.58 GHz) signal is attenuated from 5 to 13 dB. Simulations of the structure with and without graphene pads have been carried out and are in good agreement with measured results.

In this paper, a novel tunable dual-band bandpass filter (BPF) with independently controlled passbands and constant absolute bandwidth (CABW) is proposed. The CABW passbands of designed dual-band BPF are obtained using manageable electric and magnetic mix coupling. Furthermore, the multiple transmission paths from the input port to the output port are extended for extra transmission zeros, which results in modified selectivity of the proposed dual-band BPF. The tunability and switchability of the developed filter can be implemented by introducing a single bias voltage of varactors for each band. For the tunable dual-band BPF, the simulated results show that the center frequency (CF) of the first passband varies from 2.38 to 2.68 GHz, and the CF of the second passband varies from 3.28 to 3.88 GHz, while 3-dB absolute bandwidths are 101 ± 7 MHz and 98 ± 4 MHz, respectively. Moreover, the two passbands of the filter can also be independently switched by removing the voltage imposed on the varactor CV1 and CV2. The measured results agree well with simulated results, which verify the design theory.

This paper presents a two-dimensional (2D) metasurface antenna array composed of mushroom cells coupled by thin slots in the top metallization. The antenna is fed through power dividers designed in substrate-integrated waveguide technology. The antenna structure is therefore designed in a fully up-to-date integrated version. The array shows beam steering in the azimuthal plane controlled by signal amplitudes fed into particular ports at the edges of the matrix. The main advantage of this antenna is no need to use phase shifters applied in standard 2D antenna arrays. Two antenna versions have been designed, fabricated, and experimentally tested. The beam can be steered within 360° (90°) in azimuth. The steering of the beam in elevation from backward to forward directions within 40° is done by changing frequency from 21 up to 23.8 GHz. This interval is reduced to 30° by exciting the antenna simultaneously at two adjacent ports at the same amplitude.

This paper presents a dual-band bandpass filter with regular harmonic suppression. The proposed third-order filter consists of two microstrip stepped impedance resonators and single substrate integrated waveguide resonator. The mismatches in their higher order resonant frequencies are utilized to suppress the regular harmonics. The passbands are centered at f1 = 2.4 GHz and f2 = 3.5 GHz with fractional bandwidths of 5% and 7.5%, respectively. The measured midband insertion and return losses are better than 2.55 and 14.5 dB for the first, whereas for the second band, they are better than 1.95 and 14 dB. The filter offers at least 33 dB suppression of first three higher order regular harmonics of f1 and f2.

A metasurface reflector-backed wideband planar antenna is designed for millimeter-wave (mmWave) applications. A simple meandering structure is used for radiation element design, while the back side consists of a partial ground plane and parasitic elements. The utilization of meander-shaped element led to small antenna dimensions. The partial ground plane is used to achieve wide bandwidth, while the parasitic elements are used to improve the impedance matching toward higher frequency bands. To achieve high gain and directional radiation characteristics, an array of metasurfaces is placed behind the radiating element. It is observed from the simulated results that the proposed antenna system offers 17.72 GHz of impedance bandwidth in the operating range of 22.28–40 GHz, while the measured impedance bandwidth is noted to be 15.8 GHz, ranging from 23 to 38.8 GHz. Furthermore, it is observed that a metasurface-based planar antenna tends to achieve a peak gain of ≈9 dBi in the band of interest.

In order to take on arbitrary geometries, shape-changing arrays must introduce gaps between their elements. To enhance performance, this unused area can be filled with meta-material inspired switched passive networks on flexible sheets in order to compensate for the effects of increased spacing. These flexible meta-gaps can easily fold and deploy when the array changes shape. This work investigates the promise of meta-gaps through the measurement of a 5-by-5 λ-spaced array with 40 meta-gap sheets and 960 switches. The optimization and measurement problems associated with such a high-dimensional phased array are discussed. Simulated and in-situ optimization experiments are conducted to examine the differential performance of metaheuristic algorithms and characterize the underlying optimization problem. Measurement results demonstrate that in our implementation meta-gaps increase the average main beam power within the field of view (FoV) by 0.46 dB, suppress the average side lobe level within the FoV by 2 dB, and enhance the field-of-view by 23.5∘ compared to a ground-plane backed array.