Array Of Metallic Patches Research Articles

Analytical Modeling of Microwave Transmission Through Metasurfaces Made of Perforated Metal Plates, Arrays of Metal Patches, and Wire Grids

Analytical Modeling of Microwave Transmission Through Metasurfaces Made of Perforated Metal Plates, Arrays of Metal Patches, and Wire Grids

An X-shaped metasurface for high-efficiency ultra-wideband linear-to-circular and circular-to-linear polarization conversions

In this study, an X-shaped metasurface composed of an array of X-shaped metal patches printed on a grounded dielectric substrate and covered by a top dielectric layer is proposed for both linear-to-circular (LTC) and circular-to-linear (CTL) polarization conversions. Theoretical analysis and numerical simulations indicate that the metasurface can be used as both LTC and CTL reflective polarization converters. Under u- and v-polarized incidences, it can achieve LTC polarization conversion in the ultra-wide frequency band from 7.5 to 25.8 GHz with a relative bandwidth of 110%, and the polarization conversion rate (PCR) can be kept larger than 99.7% in the frequency range of 7.9-24.7 GHz. Moreover, under CP incidence, a high-efficiency ultra-wideband CTL polarization conversion can be achieved, the bandwidth and PCR are almost the same as those of the LTC polarization conversion. Finally, one experimental verification is carried out, and a reasonable agreement is observed between the simulation and experimental results.

A high efficiency ultra-wideband circular-to-linear polarization conversion metasurface

In this work, an 8-shaped metasurface is proposed for circular-to-linear (CTL) polarization conversion, which is an orthotropic anisotropic structure composed of an array of 8-shaped metal patches printed on a grounded dielectric substrate and covered by a top dielectric layer. Because the 8-shaped metasurface has an appropriate anisotropy, which can make the reflection phase difference under u- and v-polarized incidences close to +90∘ in an ultra-wide frequency range, it can be used as an ultra-wideband CTL polarization conversion metasurface. Numerical simulated results show that the 8-shaped metasurface can achieve high-efficiency ultra-wideband CTL polarization conversion, it can convert right-handed circular-polarized (RHCP) wave to a y-polarized one and convert left-handed circular-polarized (LHCP) wave to a x-polarized one in the ultra-wide frequency band from 8.34 to 26.06 GHz with a relative bandwidth of 103.0%, and the polarization conversion rate (PCR) can be kept larger than 99.6% in the total working band. Finally, an experimental verification is carried out, and a reasonable agreement is observed between the simulated and experimental results.

Analytical and numerical modeling of reconfigurable reflecting metasurfaces with capacitive memory

In this article, we develop analytical–numerical models for reconfigurable reflecting metasurfaces (MSs) formed by chessboard-patterned arrays of metallic patches. These patch arrays are loaded with varactor diodes in order to enable surface impedance and reflection phase control. Two types of analytical models are considered. The first model based on the effective medium approach is used to predict the MS reflectivity. The second model is the Bloch wave dispersion model for the same structure understood as a two-dimensional transmission line metamaterial. The latter model is used to study ways to suppress parasitic resonances in finite-size beamforming MSs. We validate the developed analytical models with full-wave numerical simulations. Finally, we propose a design of the MS control network with capacitive memory that allows for independent programming of individual unit cells of the beamforming MS.

Design of graphene‐constituted Frequency Selective Surface‐based perfect absorbers in THz regime—A circuit analysis approach

AbstractIn this article, novel designs of two different types of graphene‐based absorbers of arbitrary geometry have been investigated. The first absorber uses a graphene sheet and an array of metallic patches on silicon substrate for dual‐band absorption without the application of chemical potential. The second absorber is formed of a combination of graphene and metallic patches on the same substrate and is tunable over the frequency range 6.2–6.6 THz. Tunability is employed by electrostatic biasing of graphene patches from 0.4 to 1 eV. Using only a single layer of patterned graphene patches of two different sizes loaded around a square‐shaped metallic patch on SiO2 substrate, an absorption bandwidth of 500 GHz is exhibited. The proposed absorbers are analyzed rigorously by an equivalent circuit model (ECM). The validation of ECM analysis is done through full‐wave simulations in CST 2021.

A Back-Fire to Forward Wide-Angle Beam Steering Leaky-Wave Antenna Based on SSPPs

We demonstrate an efficient back-fire to forward wide-angle beam steering leaky-wave antenna (LWA) based on a large dispersion gradient planar spoof surface plasmon polariton (SSPP) transmission line (TL) with split-ring units. To convert the highly confined SSPP waveguiding mode to a radiation mode, two arrays of metallic patches are periodically arranged on both sides of the SSPP TL. The patches are designed as two combined half-elliptical shapes to mitigate the open stopband effect and enhance the radiation performance. We propose a theoretical method to interpret the mechanism and predict the directional pattern of the LWA. To verify the proposed method, the SSPP TL and LWA prototypes are fabricated and measured. The calculation, simulation, and experimental results match well and show that the main beam of the LWA can steer a wide range of 112° from back-fire (−90°) to the forward quadrant of 22° passing through the broadside in 6.3–11 GHz, demonstrating a large scanning rate of 2.07°/%. Furthermore, the LWA also possesses the advantages of low profile, high average gain (12 dBi), high average efficiency (95%), and low sidelobe level (<−13 dB). This work provides an alternative route to achieving wide-angle LWAs for promising microwave radar and wireless communication applications.

Coupled Solid and Inverse Antenna Stacks Above Metal Ground as Metamaterial Perfect Electromagnetic Wave Absorbers with Extreme Subwavelength Thicknesses

AbstractThe ability to completely absorb an electromagnetic (EM) wave with a material much thinner than the wavelength is a prerequisite for achieving ultracompact, flexible, and lightweight EM devices. Herein, a metamaterial microwave perfect absorber is demonstrated as thin as 1/1250 of the target wavelength by coupling an array of metal patches to inverse cross metal antennas through a dielectric separator and with a reflector placed underneath. Compared to a conventional three‐layer absorber, the modified design reduces the resonance frequency by up to tenfolds without altering the patch and dielectric layers, but by reconfiguring the induced current pathways that reorient the dipolar magnetic fields and dramatically boost the magnetic flux. With the reflector, the stack is framed for perfect absorption at the critical coupling condition, which is identified by monitoring the reflection phase shift across the resonance frequency. The study provides guidelines for shrinking the thickness further and can be extended to other frequencies.

Research on in‐band stealth of antenna based on phase gradient metasurface

AbstractIn this letter, a low in‐band radar cross section (RCS) antenna with radiation and scattering characteristics based on phase gradient metasurface (PGM) is proposed. The proposed structure consists of periodic arrays of metallic patches printed on a 1.2 mm dielectric substrate with a metallic ground plane, and the RCS is reduced between 7.8 and 12 GHz under normal incidence. Without increasing the structural complexity, some units on the metasurface are used directly as the radiators of the antenna array, which maintains the radiation characteristics of the antenna and reduces its RCS in the working band. The performance test for metasurface antenna agrees well with simulation.

Metasurface-based electromagnetic structure for electromagnetic absorption and radiation application

AbstractIn this paper, a metasurface (MS)-based multi-functional electromagnetic (EM) structure is proposed to realize its two different applications, namely absorption and radiation. The proposed structure is based on periodic arrays of disk-shaped metallic patches and split rings with four embedded lumped resistors. The metallic vias are inserted from top to bottom to connect the disk-shaped patches with a feeding network designed on the bottom layer where two p-i-n switches are embedded in the feeding network to alter the different functions of the proposed structure. For free space incident plan wave, the designed structure works as an absorber when the p-i-n switches are switched OFF. The absorber operates over a frequency band from 6.2 GHz to 8.2 GHz and unchanged over an incident angle from 0° to 30° for both TE and TM polarized incident waves. The same structure also works as a low scattering and high gain radiator when the p-i-n switches are turned ON and radiate within absorbing frequency band, i.e. from 7.5 to 8.0 GHz. The designed structure is fabricated and experimentally verified for EM absorption and radiation applications.

Dual-broadband and single ultrawideband absorbers from the terahertz to infrared regime

This paper presents the design and analysis of broadband metamaterial absorbers with single and dual absorption bands from terahertz to infrared frequencies. The absorbers are made of a composite graphene/metallic structure. A metallic patch array is printed on a ground-plane-backed dielectric slab. A graphene patch array is stacked on top of the metallic array, whereas a dielectric spacer separates the graphene and patch spacer from each other. The tunable property of the graphene surface conductivity at terahertz frequencies together with the complex permittivity of metal at the infrared regime are used to design broadband absorbers from the terahertz to infrared regime. The design is based on the combination and excitation of the plasmon polaritons of graphene and metallic patterned arrays at terahertz and infrared frequency bands, respectively. Two broad absorption bands occur from 4.56–9.02 THz and 16.95–60.23 THz with the fractional bandwidths of 67% and 112%, respectively. Furthermore, by a proper design of the parameters, a single ultrawide absorption spectra from 6.6–58.13 THz can be achieved with a fractional bandwidth 160%. In order to validate the simulation results, a circuit model-based analysis is developed, where the patterned arrays are modeled as the surface admittances, and the dielectric spacers are modeled by transmission line stubs. The results obtained by the full-wave simulations in the high-frequency structure simulator are in good agreement with the circuit model results. The absorbers show great stability with respect to the incidence angle for both the transverse electric and transverse magnetic waves.

Surface wave reflection from a metasurface termination

The reflection coefficient of a microwave surface wave incident at the termination of a metasurface is explored. Two different surface types are examined. One is a square array of square metallic patches on a dielectric-coated metallic ground plane, the other a Sievenpiper ‘mushroom’ array. In the latter the surface wave fields are more confined within the structure. Comparison of the measured surface-wave reflection spectra is made with that obtained from analytic theory and numerical modelling. The reflection coefficient is shown to be dependent on both the momentum mismatch between the surface wave and the freely propagating modes as well as the different field distributions of the two modes.

Antenna on Chip (AoC) Design Using Metasurface and SIW Technologies for THz Wireless Applications

This paper presents the design of a high-performance 0.45–0.50 THz antenna on chip (AoC) for fabrication on a 100-micron GaAs substrate. The antenna is based on metasurface and substrate-integrated waveguide (SIW) technologies. It is constituted from seven stacked layers consisting of copper patch–silicon oxide–feedline–silicon oxide–aluminium–GaAs–copper ground. The top layer consists of a 2 × 4 array of rectangular metallic patches with a row of subwavelength circular slots to transform the array into a metasurface. This essentially enlarges the effective aperture area of the antenna. The antenna is excited using a coplanar waveguide feedline that is sandwiched between the two silicon oxide layers below the patch layer. The proposed antenna structure reduces substrate loss and surface waves. The AoC has dimensions of 0.8 × 0.8 × 0.13 mm3. The results show that the proposed structure greatly enhances the antenna’s gain and radiation efficiency, and this is achieved without compromising its physical size. The antenna exhibits an average gain and efficiency of 6.5 dBi and 65%, respectively, which makes it a promising candidate for emerging terahertz applications.

Synthesis of Multiband Frequency Selective Surfaces Using Machine Learning With the Decision Tree Algorithm

This paper presents the synthesis of multiband frequency selective surfaces (FSSs) using supervised machine learning (ML) with the decision tree (DT) algorithm. The proposed FSS structure is composed of an array of metallic patches printed on a dielectric substrate for stopband spatial filtering microwave applications. The shapes of the metallic patches are based on the sunflower (helianthus annus) geometry. In the first step, a parametric analysis is performed to investigate the use of different FSS geometries, including those with circular, annular and corolla integrated patch elements, to compose the sunflower geometry, regarding multiband and polarization independent performances with size reduction. Two bioinspired FSS geometries are synthesized using supervised machine learning with the decision tree algorithm. The random forest (RF) algorithm is used to validate the decision tree algorithm and to confirm the obtained results. The numerical analysis of the proposed FSS geometries is performed using Ansoft Designer software. Prototypes are fabricated and measured. The good agreement observed between simulated and measured results has validated the proposed approach. The use of supervised machine learning with the decision tree algorithm resulted in a particularly efficient and accurate synthesis procedure due to its intuitive implementation and simplified and effective data analysis modelling.

Planar multi-angle retro-reflectors based on the wave-vector-reversion of spoof surface plasmon polaritons.

Spoof surface plasmon polariton (SSPP) is kind of sub-wavelength electromagnetic (EM) mode, which is favorable for miniaturization and thinning of EM devices. In this paper, we propose a method of designing thin planar retro-reflector that can operate under multiple incidence angles at the same frequency. The retro-reflector is composed of a transmissive phase gradient metasurface (TPGM) placed above a metallic patch array (MPA), where the former couples and decouples SSPPs while the latter supports eigen-mode propagation of SSPPs. Under oblique incident angles, the TGPM can impart 0 and π Pancharatnam-Berry (P-B) phases alternatively, producing P-B phase gradients along its surface. Incident waves can be coupled as SSPPs propagating on the MPA which will be reflected at the borders of the MPA, thus the wave-vector of SSPPs is reversed. In this way, retro-reflection can be realized under the two incidence angles θ=±45.0°. Moreover, due to mode mismatch between the TPGM and MPA under normal incidence, the retro-reflector acts like a planar metallic plate under θ=0°. To verify this method, a prototype was designed, fabricated and measured. Both the simulation and measurement results verify significant backscattering enhancement under θ=±45.0° and 0° at 10.0 GHz. This work provides an alternative method of designing planar retro-reflectors and may find applications in wireless communication, target tracking, etc.

Miniature Wideband Non-Uniform Metasurface Antenna Using Equivalent Circuit Model

A miniaturized wideband non-uniform metasurface antenna is proposed and analyzed using an equivalent circuit model. The nonuniform metasurface consists of an array of rectangular metallic patches separated by varying gaps. The effects of the varying gap widths on the resonant frequencies of the dual-mode non-uniform metasurface antenna are studied using the proposed equivalent circuit model. The resonant frequency of the first TM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">10</sub> mode decreases with narrowing of either the center or side gaps; the resonant frequency of the antiphase TM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">20</sub> mode is hardly affected by the center gap width but decreases while reducing the side gap width. The miniaturization of the metasurface antenna is therefore achieved by narrowing the side gaps, and the wide bandwidth with good impedance matching is realized by widening the center gap. A proof-of-concept prototype demonstrates a peak gain of 7.2 dBi over a -10 dB reflection coefficient bandwidth of 21.8%, with a miniaturized non-uniform metasurface of 0.46λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> × 0.49λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> × 0.06λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> (λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> is the center operating wavelength in free space) which achieves 54% size reduction compared with the earlier developed wideband antenna with a uniform metasurface of 0.7λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> × 0.7λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> × 0.06λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> .

Perfect Absorption Efficiency Circular Nanodisk Array Integrated with a Reactive Impedance Surface with High Field Enhancement.

Infrared (IR) absorbers based on a metal–insulator–metal (MIM) have been widely investigated due to their high absorption performance and simple structure. However, MIM absorbers based on ultrathin spacers suffer from low field enhancement. In this study, we propose a new MIM absorber structure to overcome this drawback. The proposed absorber utilizes a reactive impedance surface (RIS) to boost field enhancement without an ultrathin spacer and maintains near-perfect absorption by impedance matching with the vacuum. The RIS is a metallic patch array on a grounded dielectric substrate that can change its surface impedance, unlike conventional metallic reflectors. The final circular nanodisk array mounted on the optimum RIS offers an electric field enhancement factor of 180 with nearly perfect absorption of 98% at 230 THz. The proposed absorber exhibits robust performance even with a change in polarization of the incident wave. The RIS-integrated MIM absorber can be used to enhance the sensitivity of a local surface plasmon resonance (LSPR) sensor and surface-enhanced IR spectroscopy.

Bowtie Nanoantenna Array Integrated With Artificial Impedance Surfaces for Realizing High Field Enhancement and Perfect Absorption Simultaneously

High field enhancement and near-perfect absorption in nanoantennas were realized by using in-plane (between nanoantenna arms), out-of-plane (between nanoantenna and reflector), and array coupling (between nanoantennas in an array); however, it was challenging to satisfy both conditions at the same time. In this paper, we show that a bowtie nanoantenna array integrated with an artificial impedance surface can simultaneously satisfy both high field enhancement and perfect absorption. The artificial impedance surface is implemented as a metallic patch array on a grounded 50 nm-thick SiO2 substrate with reactive impedance surface (RIS) or high impedance surface (HIS) characteristic. Through the proposed design methodology, we designed a bowtie nanoantenna array on an optimum RIS patch array and achieved a high field enhancement factor (E/E0) of 228 and a nearly perfect absorption rate of 98% at 230 THz. This novel design outperforms the previously reported nanoantenna structures and the same bowtie nanoantenna array designed using a conventional grounded SiO2. We also show that the HIS-integrated bowtie antenna array cannot realize both goals at the same time because the highly reflective HIS cannot guarantee perfect absorption. The proposed RIS-combined nanoantenna array with high field enhancement and near-perfect absorption can be used for efficient infrared (IR) and optical detectors, sensors, and energy harvesting devices.

A Novel Fractal Multi-band Frequency Selective Surface

Abstract In this paper, a new multiband fractal frequency selective surface (MF-FSS) is proposed. The work presents a new fractal design methodology for FSSs with Swastika fractal patch elements. The proposed MF-FSS includes periodic arrays of metallic patches, printed on a single layer substrate. The structure parametric analysis is carried out in terms of fractal iterations, geometry elements, and unit-cell size. The simple controllable feature of the proposed structure lets us tune the given parameters of FSS geometry to achieve adjustable bandstop filter. The fractal geometry allows us to design compact structures (CP = 54%) that behave like dual-polarized bandstop filters. The designed structure is validated by means of an excellent agreement between the simulation and measurement results. Also, results show the proposed structure presents the most desirable features like fractal compactness, multiband response, dual polarization, excellent angular stability, and controllability. This work presents a fundamental structure that can be applied into the more complex and sophisticated designs in future.

Wideband Circularly Polarized Fabry–Perot Resonator Antenna in Ku-Band

A gain enhancement method is proposed for the circularly polarized (CP) magneto-electric dipole antenna (MEDA) over the whole Ku-band in this letter. Together with the CP MEDA as a feeding antenna, a single-layer partially reflecting surface made by a substrate with arrays of metal patches printed on both the top and bottom forms a Fabry–Perot resonator antenna. Five types of symmetrical patch, i.e., double printed circular, square, circular-ring, square-ring patches, and single printed circular patch, are compared and optimized for a better reflective phase property. Finally, the circular patch type is chosen because of its gentler reflective phase gradient, and hence the gain value of the CP MEDA is much enhanced over the whole operating band. A prototype is optimized and fabricated to verify the analysis. Measured results show that the 10 dB return-loss bandwidth is about 54% (11.7–19.8 GHz), the 3 dB gain bandwidth is 42.3% (11.7–17.2 GHz), and the 3 dB axial-ratio bandwidth is about 29.3% (12.4–16.8 GHz). The overlapped bandwidth of the three is 29.3%, and the maximum CP gain is 11.45 dBic at 14 GHz. A gain enhancement of about 2.1–5.2 dB is achieved as compared with the unloaded type. This method is a good option to design antennas in satellite communication with the merits of wide CP bandwidth.

High Gain and Low Grating Lobe Electrically Large Array Antenna by Using Fabry-Perot Cavity

In this paper, a high gain and low grating lobe electrically large array antenna is proposed by using Fabry-Perot cavity (FPC). The feeding array antenna is composed by elements with electrically large property (ELP) based on TM30 mode. The FPC between a ground plane and a single-layer partially reflecting surface (PRS) made by substrate with arrays of square metal patches printed on both the top and bottom surfaces is used here to narrow the beamwidth of element patterns, thus the large grating lobes of array caused by large element spacing can be avoided. By analyzing the parameters of PRS unit cell, suitable cell spacing is determined. Finally, a 2 × 2 array was fabricated and measured to validate its effectiveness. Measurements demonstrate that the gain of the array can reach up 20.9dBi at the center working frequency. When the element spacing is 1.47λ0, the maximum grating lobe level at 21GHz is only -15.5dB.