This paper presents a wideband electronically steerable circularly polarized receive phased array antenna system at K-band (17.7 GHz to 20.2 GHz) for satellite downlink applications. A scalable 64-element antenna array module in a multi-layered PCB is designed using a dual-polarized proximity-fed square-ring patch radiator with stacked circular-ring patch as the antenna element. For circular polarization (CP) radiation, the two feeds are excited orthogonally in 90° out of phase with each other. To enhance CP performance, each 2 × 2 antenna subarray is excited in a sequentially rotated manner with one Rx beamforming core chip. The 64-element array module with aperture size of 60mm × 60mm demonstrates a measured 12.5° half-power beam width (HPBW), around 22 dBic antenna gain and less than 2.5 dB axial ratio (AR) across the frequency band. The beam can be steered to ±60° in all planes without grating lobes. Furthermore, to demonstrate the scalability, a 256-element phased array is prototyped and measured.

An electronic switched-beam grid-array antenna (GAA) at 28.0 GHz is investigated. The proposed antenna panel includes of a sixteen-port GAA integrated with RF switching circuit that consists of five RF switches and a separate control panel. The sixteen beams can be electronically switched/steered with a beam coverage of ±22° and measured antenna gain of >14.0 dBi at 28.0 GHz.

A single-feed miniaturized wideband circularly polarized (CP) antenna with metasurface is planned for L-band applications. The projected multilayered antenna comprises of a patch radiator with embedded ring-shaped slot and grounded-via, a stacked slit-slotted-circular patch, a metasurface with $5\times 5$ -unit cells, and a coaxial feeding probe. An antenna prototype at L-band exhibits -10-dB reflection coefficient $(\vert \mathrm{S}_{11}\vert)$ bandwidth of 15.7% (1.488 GHz-1.742 GHz), 3-dB axial ratio (AR) bandwidth of 11.0% (1.50 GHz-1.675 GHz), and gain of $> 5.0\text{dBic}$ within the 3-dB AR-bandwidth with an overall size of $\boldsymbol{0.375 \lambda_{0} \times 0.375 \lambda_{0} \times 0.065 \lambda_{0}}$ at 1.5 GHz.

A compact metasurface-based circularly polarized (CP) dielectric resonator antenna (DRA) is proposed with wideband characteristics. The antenna forms a very simple structure, composed of a rectangular DR, a single coaxial probe, and plus-shaped unit cells-based metasurface. The metasurface is realized on a grounded FR-4 substrate. Next, a rectangular DR is loaded centrally over the metasurface. The DR is fed with a perturbed probe feed at an appropriate angle of ( $\theta $ =29°), along the diagonal line. Thus, a novel hybrid technique involving the angle of feed location from the center of DR, and the N $\times $ N unit cells-based metasurface is utilized for generating a wideband CP radiation. The resonance from the rectangular DR and surface waves along the $7\times $ 7 plus-shaped unit cells-based metasurface is exploited to achieve a wide 3-dB axial ratio (AR) and impedance matching bandwidth. The fabricated antenna prototype used for the validation of predicted results confirms the successful implementation of the proposed technique. Measured results demonstrate a wide impedance bandwidth of 32% (3.6 GHz - 7.0 GHz) and an overlapping 3-dB AR bandwidth of 20.4% (4.2 GHz - 5.2 GHz). Moreover, the antenna adopts a left-hand circular polarization (LHCP) with 6–7 dBic measured gain within the operational frequency range. Overall, the proposed antenna offers low-profile, simplicity, ease of design, and high performance.

Metasurface (MS) absorbers with polarization-insensitivity and wide-angle reception features have attracted much attention due to their unique absorption property. A polarization-insensitive broadband MS absorber structure, having wide-angle reception based on square split-ring resonators (SSRRs) and loaded with lumped resistors, is proposed in this paper. The proposed MS unit cell consists of a fixed-thickness FR4 dielectric substrate and a variable air-thickness substrate. The simulation results show that the proposed MS absorber is stable across a wide angular range for both normal and oblique incidences. Furthermore, the simulated results show that some parameters, such as unit-cell geometry and lumped resistors, can be varied to improve the performance of the MS absorber. The experimental results indicate that the proposed MS absorber can be achieved an absorption higher than 90% across the frequency range from 1.89 GHz to 6.85 GHz with a relative bandwidth of 113%, which is in agreement with simulation results. Thus, the proposed MS absorber can be more suitable in RF energy harvesting or wireless power transfer applications.

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 circularly polarized (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 global navigation satellite system (GNSS) L1-band of 1.6 GHz with CP w and 2.07 GHz with a LP for 5G New Radio (NR) applications. An integrated ring-slot with via acts as a composite right/left-handed 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 0.32λ 0 ×0.32λ 0 ×0.0264λ 0 (λ 0 is the free-space wavelength at 1.6 GHz) are: the bandwidth of 5.6% (1.585 GHz - 1.675 GHz) at the L-band and 0.75% (2.04GHz-2.07GHz) at the S-band for 10-dB return loss; 2.5% (1.59GHz-1.63GHz) at the L-band for 3-dB axial ratio (AR); peak gain of 4.9 dBic at 1.62 GHz and 4.0 dBi at 2.07 GHz.

In this article, a miniaturized reconfigurable 4-element ultra-wideband (UWB) multiple-input-multiple-output (MIMO) antenna is proposed to operate from 2.52 to 24 GHz, and studied using characteristics mode analysis (CMA). Initially, a 1-element antenna is designed and then extended to 4-element MIMO configuration. The MIMO antenna achieves design merits by orthogonally sorting fractal radiators for miniaturization, a Gamma-shaped slot for band-notching and rotationally symmetric connected ground for isolation. CMA is explored to study the band-notched behavior effect in antenna, which shows two operating modes, NM-mode and NB-mode (NM: normal-mode, NB: Notched-mode). The modal metrics is discussed for both modes giving an insights on the bandwidth and radiation potentials. Four RF p-i-n diodes are mounted at the Gamma-shaped slot orifice on each antennas, to control the band-notched operation. At OFF-state, the antenna is with wide-band-rejection from 3.7 to 8.87 GHz and at ON-state, it works in pure UWB mode. To demonstrate its feasibility, a fabricated antenna of size 24 mm x 24 mm is experimented which are in good agreements with simulated results.

Compact, low-profile metasurface-based wideband and wide dual-band circularly polarized (CP) dielectric resonator antennas (DRAs) are presented in this paper. The rectangular-shaped DRs are loaded over two different types of strategic 7 × 7 metasurface unit cells including a "+" shape metasurface for single-band and square-slotted shape metasurface for dual-band performance. The DRs are fed diagonally with a single perturbed probe feed which is placed at an appropriate angle of 29°. Thus, the hybrid design combination of metasurface unit cells together with the angle of feed location from the center of DRs generates wideband CP radiation with enhanced 3-dB Axial Ratio (AR) and wide impedance matching bandwidths. Proposed antennas are successfully implemented and fabricated prototypes are measured demonstrating significant performance enhancement.

A miniaturized four-element antenna of 20 mm × 20 mm with edge-to-edge distance of 4.9 mm between the array antennas operating from 4.6–8.6 GHz is investigated in this article. The antenna consists of 4 × integrated dipole driven elements, and complementary split ring resonator (CSRR) metacells are loaded on the both sides of each dipole arms. The loaded meta-couplers magnetically couple to dipole drivers, and the induced resonance effect improves the 10-dB impedance bandwidth (IBW) to 60.6%. To improvise the isolation between antenna elements, metallic vias are implemented that trap electromagnetic (EM)-surface waves to condense into the ground. So, the meta-couplers induce electromagnetic (EM)-propagation as surface wave trapments for radiation and decouple near-field condensed currents, acting as couplers/decouplers. The maximum isolation achieved is >−22.5 dB without any external decoupling network. The diversity parameters indicate good attributes in isotropic, indoor, and outdoor channel environments with an envelope correlation coefficient (ECC) < 0.165 and realized gain of 5.5 dBi with average radiation efficiency of 80–90% in the desired operating bands. An equivalent circuit model using lumped components is designed for the proposed four-element antenna. For validation, a prototype antenna is fabricated and measured to be implemented in 5G applications, which shows good correlation with the full-wave simulated results.

A broadband electromagnetic metasurface (MS) absorber with a wide-angle coverage is designed and discussed for energy harvesting applications. The proposed MS absorber consists of two split-ring resonators (SRR) forming an X-shaped in the middle and layout is designed on FR4 dielectric substrate. An air gap layer is separated between the dielectric substrate and a ground plane. At normal incidence...

In this research article, a wideband mobile antenna with defected ground structure (DGS) is designed using characteristics mode analysis. It consists of a modified crescent-shaped monopole antenna (M-mode), L-shaped stub (S-mode), and DGS element (slot modes). Here, the fundamental resonating modes of M- and S-mode are induced to operate in the integration mode (I-mode) to obtain good impedance bandwidth (IBW). The DGS is implemented in ground plane to get slot modes (1 and 2). By combining slot modes with M-mode and S-mode, it exhibits broadened IBW (i.e., C-mode), is suitable for the coverage of mobile bands (sub-6 GHz frequency bands). For the clarity, modal investigation is performed at each critical stages of antenna designing process and the modal metrics like modal significance, characteristics angle (beta(n)), Eigen values (lambda(n)), modal currents, and modal patterns are extracted by using Computer Simulation Technology (CST) Studio Suite. The proposed monopole antenna operates in multiband for wireless applications, that is, 880-960 MHz, 2.3-2.4 GHz, 2.4-2.483 GHz, 3.3-4.2 MHz, 3.3-3.8 GHz, 5.15-5.85 GHz, and WLAN (IEEE 802.11 b/g/n) respectively with measured gain of 3-5.5 dBi. A prototype of proposed antenna is fabricated and measured, which shows good agreements with simulation. To validate, averaged specific absorption rate (SAR) is investigated with 3D voxel phantom human head and hand model. The observed SAR 1 g lies between 0.0014 and 0.0462 W/kg in the operating bands, which are under the limits prescribed by the Federal Communications Commission (FCC). From the above outcomes, it can be potentially used in the mobile handsets and also, can be extended to hybrid wireless cellular communication networks & potential applications like RF energy harvesting.

A wideband compact frequency beam scanning (leaky-wave antenna, LWA) antenna based on composite (right-handed and left-handed) unit cells is proposed for 5G millimeter wave applications. The antenna involves of fifteen composite right/left-handed (CRLH) unit cells with metallic-vias and microstrip transitions. Novel unit-cell-based antenna designed which can be achieved nearly linear frequency scanning within the frequency range from 24.0 GHz to 32.0 GHz with uniform gain of ≈ 8 dBi.

A wide-coverage suspended metasurface (MS) electromagnetic (EM) energy harvester for ISM band applications is designed and analyzed. The proposed MS harvester is printed on a thin and low-loss substrate material and suspended with an air gap to increase the efficiency of the MS harvester. At normal-incidence, the proposed MS harvester is achieved a higher absorption response of about 90% across the frequencies from 2.14 GHz to 2.64 GHz. At oblique incidence angles, the AC power efficiency of 93.7%, 77.2% and 64% is achieved at incident angles of 15 o, 30 o and 45 o, respectively.

A compact composite right/left-handed (CRLH)-based dualband rectenna is proposed for electromagnetic (EM) energy harvesting at the operating frequencies of Wi-Fi (2.5 GHz) and Worldwide Interoperability for Microwave Access (WiMAX) (3.6 GHz) bands. The rectenna consists of a dual-band antenna and dual-band rectifier. The antenna is realized in a microstrip topology using a balanced CRLH transmission line (TL) with an open termination. It measures 0.36 # 0.2 # 0.00049 mo (mo is the free-space guided wavelength) at 2.5 GHz and operates at 2.5 and 3.6 GHz, with an operating bandwidth of 4.75 and 3.3%, respectively, and a peak gain of 2.6 decibels relative to isotropic (dBi) at 2.5 GHz and 1.6 dBi at 3.6 GHz. The dual-band rectifier is designed using a novel CRLH-based microstrip topology composed of microstrip lines and lumped components. The overall rectifier volume is 0.3 # 0.2 # 0.0005 mo at 2.5 GHz. The measured radio-frequency (RF)?dc conversion efficiency is more than 59% at 2.5 GHz and 41% at 3.6 GHz, for an input power of 2 dB milliwatts (dBm) in both cases.

Energy harvesting (EH) or scavenging is recognized as harvesting energy from ambient energy sources in the surrounding environment. This paper reports a literature review on radio frequency (RF) EH using different metasurface/metamaterial structures based on split-ring resonators (SRRs), electric inductive-capacitive (ELC) resonators, square-patch unit cells, square-ring unit cells, etc. The essential parameters in rectifying antenna (rectenna) design are included, such as receiving antenna efficiency, conversion efficiency, dimensions, supporting substrate properties, frequency band, and overall performance, etc. It is noted that rectenna design using conventional antennas such as microstrip antennas, monopole antennas, slot antennas, dielectric resonator antennas, etc. suffers from low power conversion efficiency with larger size. To overcome the above-mentioned constraints and enhance the conversion efficiency with smaller size, metasurface/metamaterial structures are used as EH collectors. An introduction to EH is discussed, followed by an overview of energy sources in the ambient environment. Several hypothetical and experimental studies on metasurface-based EH systems are summarized.

In this article, a low profile circularly polarized (CP) antenna with wide 3-dB axial ratio beamwidth (ARBW) is presented. Two-pair of parallel slots are etched on a circular patch and manifested as magnetic dipoles (MDs). These narrow slots are arranged symmetrically about the axes, and one pair is orthogonal to another pair of slots. The philosophy of CP radiation across a wide angular range strongly depends on the spacing between the paired-dipoles, for example spacing of $0.22\lambda _{0}$ , two-orthogonal far-field radiated components become equal across a wide-angle. Moreover, this particular spacing between the paired-dipoles provides a symmetrical electric field distribution along the periphery of the patch, which ensures the broadside LHCP radiation with wide 3-dB ARBW of 228° and 214° at the plane of $\varphi = 0^{\circ }$ and $\varphi = 90^{\circ }$ , respectively. The measured results from the fabricated prototype exhibit good agreement with the simulated results. The antenna has impedance bandwidth (IBW) and CP bandwidth (CPBW) of 2.6% (64 MHz), and 0.9% (22 MHz), respectively. The broadside radiation holds antenna gain higher than 5 dBic across the entire CPBW.

A microwave metasurface (MS) absorber for ISM band applications is proposed and studied. The proposed MS structure consists of two metallic layers separated by two dielectric FR4 materials with a thickness of 1.6 mm. An air gap with a thickness of 10 mm placed between the dielectric layers. The proposed MS absorber exhibits near-unity absorption and wider absorption bandwidth at an operating frequency of 2.4 GHz under normal incidence. For oblique incidence, it shows wider absorption bandwidth and an absorption value of more than 93% for different incident angles for TEM-mode and more than 93% at for TE mode. Moreover, a numerical analysis presented to explain the physical interpretation of the absorption mechanism in detail.

Electromagnetic Compatibility (EMC) engineers should self-check the antenna’s condition and parameters, including Antenna Factor (AF) and Gain, continuously, by calibrating the antenna. Therefore, several analyses have been done to compare between SAM and SSM in EMC testing lab. Based on the analysis, the antenna to be used inside a 3 m semi-anechoic chamber need to be positioned 1.5 m above the ground plane to avoid the reflection. The Antenna Factor (AF) results show a good agreement with manufacturer data. SAM is recommended as a calibration method in the semi-anechoic chamber because the percentage error is 5% which is lower compared with SSM (18%). This is due to the site imperfection in the EMC lab. The uncertainty for the EMC lab is up to ±4 dB, compared to the calibration test site where allowed uncertainty is ±1 dB. Therefore, an absorber needs to be placed between two antennas. In addition, the phase center of the reference antenna needs to take into consideration for highly accurate AF.

A wide-angle and polarization-insensitive metasurface instead of traditional antenna is built as the primary ambient energy harvester. Proposed metasurface harvester can receive electromagnetic (EM) energy from wide angles and received rectified power can be combined by DC combining for EM harvesting system. The reflection coefficient, power distribution, EM harvesting efficiency, and absorption efficiency on the normal and oblique incidences are studied and presented. For a single unit cell with periodic boundary condition, simulation results exhibit that the absorption and harvesting efficiencies are more than 98 and 96%, respectively, under normal incidence at an operating frequency of 2.4 GHz. The results also show that on the oblique incidence of 0°, the maximum absorption efficiency is more than 98% and it can achieve more than 80% reception efficiency at the incidence angle of ±60°.

In this letter, a low-profile circularly polarized (CP) narrow-slots slotted-patch antenna for wide 3 dB axial-ratio beamwidth (ARBW) performance is presented. It consists of two pairs of narrow slots along the diagonal lines of a square patch with a single feed. These pairs of narrow slots are conceived and placed to serve as magnetic dipoles with quarter-wavelength separation, forcing the amplitude of the orthogonal electric field components to be equal across a wide angle. The 3 dB ARBW of the CP antenna is a strong function of the mutual magnetic field, which is feasible to alter with different parameters of the slot. The location, dimensions, and gap between the slots are tuned to achieve wide 3 dB ARBW. Measured results of the fabricated prototype exhibit 3 dB ARBW of 226° with ARmin of 0.52 dB and 198° with ARmin of 1.61 dB in two principal planes at $\boldsymbol{\varphi } = \text{0}^\circ $ and $\boldsymbol{\varphi } = \text{90}^\circ $, respectively. The antenna offers impedance bandwidth of 85 MHz (2.448–2.533 GHz) and CP bandwidth (CPBW) of 23 MHz (2.474–2.497 GHz). The minimum peak gain is 3.87 dBic in the broadside direction.