Metasurface Antenna Research Articles

High Isolation and Low Cross-Polarization of Low-Profile Dual-Polarized Antennas via Metasurface Mode Optimization

A low-profile dual-polarized metasurface antenna with high isolation and low cross-polarization is proposed in this communication. The proposed metasurface consists of an array of $4\times 4$ patches. Through characteristic mode analysis (CMA), a pair of degenerate modes is identified to achieve the desired radiation features. By modifying the patches of the metasurface, the strongest mode current distributions of the two modes are moved from the center to the edge of the metasurface. One feed port can efficiently excite only one particular mode, and the other mode cannot be excited simultaneously. Each of the modes are differentially fed using two Y-shaped microstrip lines via two slots. As a result, both high isolation and low cross-polarization can be obtained. The simulation and experimental results show that the proposed antenna achieves not only a low profile of $0.05\lambda _{0}$ (where $\lambda _{0}$ is the free-space wavelength at the center resonant frequency) but also a broad impedance bandwidth of 36% and a high isolation of 53 dB. In particular, the enhanced cross-polarization discrimination (XPD) is lower than −40 dB at the broadside, lower than −33 dB within ±30° of the main lobe, and lower than −28 dB within ±60° of the main lobe.

Power balance and efficiency of metasurface antennas

This paper presents two methods for the efficient evaluation of the power balance in circular metasurface (MTS) antennas implementing arbitrary modulated surface impedances on a grounded dielectric slab. Both methods assume the surface current in the homogenized MTS to be known. The first technique relies on the surface current expansion with Fourier-Bessel basis functions (FBBF) and proceeds by integration of the Poynting vector on a closed surface. The second method is based on the evaluation of the residue of the electric field spectrum at the surface-wave (SW) pole, and is demonstrated by using a current expansion in Gaussian ring basis functions (GRBF). The surface current expansions can be directly obtained either by analyzing the antenna with a Method of Moments (MoM) tool for homogenized MTSs based on FBBF or GRBF, or derived by a projection process. From there, the power contributions, namely the total power delivered by the feed, the radiated power, the SW power, and the Ohmic power losses in the dielectric are computed. Several efficiency metrics are presented and discussed: tapering efficiency, conversion efficiency, loss factor, and diffraction factor. Since the MTS apertures at hand are leaky-wave (LW) antennas, the designer must find a compromise between the aperture efficiency and the conversion efficiency. This requires accurate and fast computational techniques for the efficiency. The present paper demonstrates for the first time that the efficiency of MTS antenna devices can be accurately evaluated in a few minutes. The compromise that should be made during the design process between the tapering efficiency and the conversion efficiency is highlighted. The impact on the efficiency of isotropic versus anisotropic MTS, uniform versus non-uniform modulation index, is analyzed. An excellent agreement is obtained between both approaches, commercial software, and experimental data.

Miniaturized Wideband Planar Antenna Using Interembedded Metasurface Structure

One kind of interembedded metasurface (MS) structure is proposed and applied to realize miniaturized wideband MS antennas (MSA). Different from conventional MSA, the proposed interembedded MSs are formed by etching slots on the radiating patch with various sawtooth schemes rather than rectangular gaps. Consequently, the resonance frequency of MSA can be decreased due to introducing those interdigital-like capacitances, while obvious miniaturization can be realized accordingly. By optimizing the parameters of the sawtooth radiating slots, a miniaturized antenna using cross-shaped interembedded MS is proposed, achieving an impedance bandwidth of 35.08% and a high gain of about 8.25 dBi with a compact overall size of 0.66λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> ×0.66λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> . Moreover, one further miniaturized antenna using modified cross-shaped interembedded MS is also presented, realizing a larger impedance bandwidth of 41.35% and a high gain of about 6.62 dBi with a smaller aperture of 0.48λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> ×0.48λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> . Compared with conventional MSA, 42% overall size reduction and larger bandwidth can be obtained. The design approach may provide a feasible solution to realize compact MSAs with the unique advantages of large bandwidth, low profile, low cost, and easy fabrication. Due to above good features, the proposed antenna can be a promising candidate for applications in modern wideband wireless communication systems.

Resonant Metasurface Antennas With Resonant Apertures: Characteristic Mode Analysis and Dual-Polarized Broadband Low-Profile Design

Resonant metasurface (MTS) antennas (RMAs) are antennas leveraging unusual standing-wave modes of truncated MTS. By introducing resonant exciters, such as wire (electric currents), aperture (magnetic currents), or both, the antenna bandwidth can be improved. However, the contributing modes of apertures are not well recognized. A systematic framework is formulated for the characteristic mode analysis (CMA) and design of RMAs involving resonant apertures, by designing a low-profile wideband dual-polarized RMAs fed by slot arrays at 5 GHz Wi-Fi bands. Unlike regular microstrip patches, the aperture-backed MTS supports two fundamental TM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">03</sub> modes of different symmetries. Even and odd symmetries are also observed for the aperture modes. By calculating the radiating power of individual mode, quantitative evidence is provided to clarify the operating principle of RMAs with resonant apertures that the bandwidth improvement and high-isolations are due to the modes from both the MTS and the aperture, rather than from individual. The overall size of the proposed antenna is λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">L</sub> ×λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">L</sub> ×0.058λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">L</sub> ( λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">L</sub> is the free-space wavelength at 4.8 GHz). The measured bandwidth is 25% (4.8-6.2 GHz) with |S <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</sub> | <; -10 dB, |S <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">21</sub> | <; -34 dB, boresight gain of 8-10 dBi and cross-polarization level better than -28 dB.

Low-Profile Ultrawideband Circularly Polarized Metasurface Antenna Array

A compact low-profile ultrawideband circularly polarized (CP) metasurface antenna (MSA) array is presented in this letter. The array consists of 2 × 2 sequentially rotated symmetric MSA elements and a wideband four-way feeding network providing stable phases of 0°, 90°, 180°, and 270°. By using the constructed feeding network and MSA element, the CP array can achieve an ultrawideband CP performance with a low profile of 0.05λ L . The measured results show that the proposed MSA array achieves the 10 dB impedance bandwidth of 97.2%, 3 dB axial ratio bandwidth of 83.2%, and 3 dB gain variation bandwidth of 73.8%. Compared with the other designs in published literatures, the proposed CP MSA array owns the advantages of low profile with a simple structure and good CP performance without any air gap, thus indicating a promising candidate in compact wideband wireless systems.

A Broadband Low-Profile Dual-Linearly Polarized Dipole-Driven Metasurface Antenna

A low-profile broadband metasurface antenna (MSA) with dual-linear polarization is developed. The developed MSA mainly consists of a 4 × 4 grid-slotted patch array, two pairs of orthogonally printed feeding dipole strips, two vertically grounded and orthogonally placed microstrip Γ-shaped feeding structures, and an intact ground plane. It is demonstrated that the strip-excited MSA excites a leaky wave mode, a surface wave mode, and a dipole mode to provide a wide operational bandwidth. The prototype, with an overall size of 0.65 λ0 × 0.65 λ0 × 0.07 λ0 (λ0 is the wavelength in free space at the center operating frequency) was fabricated and measured. Three modes with broadside radiation patterns for each port are simultaneously excited to create a wide impedance bandwidth 36% with the average gain value 9.3 dBi. Moreover, the port-to-port isolation and the cross-polarization discrimination (XPD) are, respectively, higher than 26 and 25 dB.

Flat Gain Broadband Metasurface Antennas

Modulated metasurface (MTS) antennas can provide a broadside pencil beam at the frequency where the cylindrical surface wave (SW) wavelength matches the period of the impedance modulation. For modulations with constant period, the mismatch between the SW wavelength and the period imposes a limitation on the gain-bandwidth product. However, this limitation can be overcome by shaping the local period as a function of the radial distance. Doing so, we generate an annular active region on the antenna aperture, where the SW-to-impedance interaction mainly occurs. Such active region moves from the antenna center to the circular rim as the frequency decreases. This article shows that one can optimize the profile of the local periodicity function to obtain broadside pencil beams over large bandwidths, while preserving the flatness of the gain versus frequency response and a good stability of the phase center. The antenna performances so obtained are really unique for flat antennas based on printed technology. Finally, we present a simple formula for the product between average gain and bandwidth, which gradually blends into the already known expression for modulations with constant period. This formula establishes an absolute limit of the gain-bandwidth product, which only depends on the wavelength-normalized antenna radius at the central frequency.

Wideband high‐gain multiresonance antenna based on polarization‐dependent metasurface

AbstractIn this article, a novel polarization‐dependent metasurface (PDMS) structure is presented and applied to realize a wideband high‐gain antenna with multiple resonances. The PDMS element is obtained by cutting slots into the square patch unit cell of conventional metasurface (MS). Very different from the conventional MS structure, the proposed PDMS element exhibits different reflection phases and resonance frequencies, depending on the polarization state of the incident plane wave. By properly tailoring the reflection‐phase curves under different polarizations, a proper PDMS structure is introduced. Then, by arranging the PDMS elements along different orientations, a multiresonance radiator can be realized. When applying the proposed radiator to the slot‐coupled MS antenna, one broadband PDMS‐based antenna with multiple adjacent resonance frequencies can be realized by the combination of coupling slot‐mode and PDMS modes. For verification, a PDMS radiator with 4 × 4 unit cells is designed accordingly and applied to realize one C‐band broadband PDMS‐based antenna in a low profile (0.06 λ0). The measured results of the fabricated prototype PDMS‐based antenna exhibit a large –10 dB impedance bandwidth of 55% (4.31‐7.58 GHz), a maximum available gain of 10.898 dBi, and a 2‐dB gain bandwidth of 30.81% (5.1‐6.96 GHz).

Design of broadband circularly polarized metasurface antenna array with gain enhancement

In this paper, a broadband right-hand-circular polarization metasurface antenna array is designed to satisfy the specific satellite-based installation platform. The slot coupling patch antenna is employed as element to construct the 4 × 4 array and narrow beam can be obtained by this way. The gain and performance of the antenna array are improved by adding the metasurface parasitic patch patches. By employing the H-shape slot coupling feed structure arranged in T-shape and broadband 90° phase shifter, the antenna can achieve the broadband circularly polarized characteristics. And by utilizing Wilkinson power divider, broad impedance bandwidth can be obtained. The simulated results indicate that the S11 of the antenna array is below 10 dB in the operating band from 6.4 to 13.9 GHz (73.9%), the AR bandwidth is from 7 to 13.3 GHz (62.1%). And the gain is more than 15.4 dB in the X-band with the peak gain 19.7dBi at 11.3 GHz. The antenna array is fabricated to validate the design. The measured results and simulated results agree well, broadband bandwidth, circularly polarized, narrow beam, and low profile are achieved. The operating band of the array covers the whole X-band which is suitable for the actual satellite-based antenna applications.

A wideband and multi-mode metasurface antenna with gain enhancement

A metasurface radiator composed of nonuniform patches with gain improvement is proposed in this paper. On the center of the ground plane, an anomalous slot is etched to feed the antenna by a microstrip line. Along the slotline resonate, two uniform slot stubs are added symmetrically near the nulls of the electric field. And an extra radiation mode is introduced. Then, through merging with the full-wavelength provided by the initial slot, a wideband slot antenna with two resonances is obtained. The operating bandwidth is broadened from 17.8% to 27.2%. Besides, nonuniform patches are introduced to modify the gain of the antenna with 1.5 dBi. A 2 × 2 array is fabricated to validate the design, and the whole dimension is 2.26λ0 × 2.26λ0 × 0.08λ0. The simulated and measured results exhibit that the impedance bandwidth is 43.3% and the gain is 13.4–17.6 dBi during the operating band.

A Compact Dual-Band Metasurface-Based Antenna for Wearable Medical Body-Area Network Devices

A compact, low-profile wearable antenna capable of operation within the 5.1–5.46 GHz and 5.7–5.85 GHz medical body-area network band is suggested to make the antenna better for wearable devices. The integrated metasurface (MSs) antenna consists of as few as array of three wan-shaped components, directly below the planar waveguide-fed monopole antenna. The measurement of the integrated antenna is 0.56λ0×0.56λ0×0.08λ0, all while achieving an average gain of 8.2 dBi in working frequency and a front-to-back ratio (FB) in excess of 19 dB. As demonstrated by in-depth examination, the antenna performs exceptionally well in withstanding the distortion of structure, far superior to planar monopole antenna. Additionally, the metasurface enables the specific absorption rate (SAR) low to 0.84 W/kg, which makes this type of antenna suited to application in different wearable devices.

Characteristic Mode Analysis of a Nonuniform Metasurface Antenna for Wearable Applications

A novel nonuniform metasurface antenna is designed based on the characteristic mode analysis for wearable applications. A metasurface layer consists of a 3 × 3 unit cell array, in which the center and corner cells are rotated counterclockwise, whereas the other four unit cells are rotated in the opposite direction with a same rotation angle. The structure of a nonuniform metasurface is optimized according to the modal significance curves and surface currents, which resulted that mode 1 and mode 2 are combined to widen the bandwidth, which can cover the 5 GHz WLAN band. The volume of the proposed antenna is equal to a cylinder with a diameter of 55 mm and a thickness of 4 mm. The measured efficiency is greater than 80% and the average gain can achieve 7.63 dBi in the working band. The proposed antenna is harmless to human body, which can be evidenced by the simulated 1 and 10 g averaged specific absorption rate values.

Grating lobe suppression in metasurface antenna arrays with a waveguide feed layer.

Metasurface antennas offer an alternative architecture to electrically large beamsteering arrays often used in radar and communications. The advantages offered by metasurfaces are enabled by the use of passive, tunable radiating elements. While these metamaterial elements do not exhibit the full range of phase tuning as can be obtained with phase shifters, they can be engineered to provide a similar level of performance with much lower power requirements and circuit complexity. Due to the limited phase and magnitude control, however, larger metasurface apertures can be susceptible to strong grating lobes which result from an unwanted periodic magnitude response that accompanies an ideal phase pattern. In this work, we combine antenna theory with analytical modeling of metamaterial elements to mathematically reveal the source of such grating lobes. To circumvent this problem, we introduce a compensatory waveguide feed layer designed to suppress grating lobes in metasurface antenna arrays. The waveguide feed layer helps metasurface antennas approach the performance of phased arrays from an improved hardware platform, poising metasurface antennas to impact a variety of beamforming applications.

A multistate high gain antenna based on metasurface

A multi-state high gain antenna based on metasurface is proposed. The antenna is composed of two stacking layers and a ground plane. The metasurface is constituted by two layers with the same size. And both of the two layers contain a copper patch array which is formed by 4 × 4 square copper cells uniformly distributed along x and y directions. The metasurface antenna is excited by the aperture coupled structure. The structure is consists of an anomaly microstrip line and a narrow slot etched in the ground plane. Genetic algorithm (GA) is adopted to optimize all the parameters and obtain the best performance of the metasurface antenna. By appropriately choosing the dimensions of the antenna, the proposed antenna can be achieved with the impedance bandwidth (RL≥10 dB) of about 340 MHz (7.8% at 4.36 GHz), 180 MHz (3.6% at 5.02 GHz), and 2800 MHz (41.1% at 6.81 GHz). The peak gain of the proposed antenna is 10.1dBi, 6.9 dBi, and 10.5dBi at 4.26 GHz, 5 GHz, and 7 GHz. In addition, the proposed metasurface antenna can work in multistate, which makes it an excellent candidate for practical applications.

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> .

Low-Profile Broadband Patch-Driven Metasurface Antenna

In this letter, a patch-driven low-profile broadband metasurface (MTS) antenna is proposed. The novel antenna is constituted utilizing an aperture coupled patch and proposed configurations of finite-sized artificial magnetic conductor. With the surrounding MTS excited by the surface wave introduced through the center patch, an additional TM resonance is generated and a wideband impedance matching is achieved. The performance and operating mechanism of the proposed antenna are investigated and analyzed. To demonstrate the concept, a 1 × 4 array with an overall thickness of 0.047 λ <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 free-space wavelength at 28 GHz) is successfully implemented through advanced substrate manufacturing process. The obtained impedance bandwidth for reflection coefficient below -10 dB is 27.1% with a maximum realized gain of 13.6 dBi.

Double‐layer metasurface‐based low profile broadband X‐band microstrip antenna

In this paper, a novel technology based on double-layer metasurfaces is proposed in order to broaden the bandwidth of microstrip antennas, which has been verified in X-band linearly polarised and circularly polarised antennas. Referring to the conventional metasurface antenna that employs slot-coupled feeding, these designs add an extra metasurface between the radiation patch and the ground plane so as to establish dual resonance modes, TM10 and TM20. Following the adoption of the composite right/left-handed transmission lines principle, this technique aims to adjust the propagation constant in the right-hand region by introducing parallel inductors and capacitors to widen the dual resonant frequencies' interval, thereby realising a broadband antenna. In addition, the interlayer metasurface may also be utilised as a director to balance the E-field of the radiation patch. A linearly polarised double-layer metasurface antenna with a size of 0.8 0.8 0.058 (wavelength in free space at the centre frequency) is filled with F4B substrate with a dielectric constant of 2.2. It finally realises an impedance matching bandwidth (VSWR 2) from 8.41 to 11.67 GHz, occupying about 32.47 of the centre frequency. This circularly polarised antenna attains both an impedance matching bandwidth of 32.44 (i.e. 8.29–11.5 GHz) and an axial-ratio bandwidth of 19.72 (i.e. 9.6–11.7 GHz).

A Gain-Enhanced Slotted Patch Antenna Using Metasurface as Superstrate Configuration

In this paper, a novel, compact, high-gain, directive, and superstrate configuration-based metasurface (MS) antenna has been designed, which incorporates a fractal-shaped slotted patch having a periodic arrangement of square patches along with a shorting via at its center and a couple of rectangular slots in the ground plane. The MS is designed over the FR4 dielectric by introducing a periodic arrangement of unit cells in which the unit cell is structured by a C-type patterned patch in the center surrounded by a couple of L-type-shaped patches. The MS is separated by a layer of Teflon from the conventional patch antenna designed over the FR4 dielectric, thereby acting as a superstrate. The proposed antenna provides good impedance matching across the frequency region of 10.14-10.94 GHz with a unidirectional radiation pattern. A fractional bandwidth of 7.6% and a maximum return loss of 24 dB have been realized at 10.44 GHz. The measured realized gain of 7.57 dBi was obtained at the same operating frequency. As the proposed antenna is more efficient, it can be promoted for X-band operations, such as satellite communication, defense purpose, and medical supervision.

Wideband, Electrically Small, Near-Field Resonant Parasitic Dipole Antenna With Stable Radiation Performance

A wideband, electrically small, and near-field resonant parasitic (NFRP) dipole antenna with stable radiation performance is presented. Inspired by recent metasurface antennas (MSAs), a coax-fed dipole antenna is loaded with a specially-engineered interdigitated NFRP element. It exhibits identical operating mechanisms to a developed electrically large slot-fed MSA, i.e., it has the similar adjacent fundamental mode and antiphase mode, and thus has a wide bandwidth property and uniform radiation patterns. The electrically small prototype was fabricated and measured. The measured results, in good agreement with their simulated values, demonstrate a wide 14.4% −10 dB impedance bandwidth along with a stable realized gain of 1.4 dBi over the entire band. Moreover, stable and uniform radiation patterns together with high radiation efficiency values were also measured. These performance characteristics make the reported electrically small antennas attractive for wideband and space-limited applications.

On the Use of Entire-Domain Basis Functions and Fast Factorizations for the Design of Modulated Metasurface

Entire-domain, spectral basis functions (BFs) have witnessed recent interest in the integral-equation analysis of large metasurface (MS) antennas modeled via homogenized impedance boundary conditions. We present a formulation employing classical Galerkin test via Rao–Wilton–Glisson functions yet assembled to represent entire-domain div-conforming BFs for the shape of interest (e.g., circular/coaxial waveguide modes). On the one hand, the rationale is that entire-domain, spectral BFs afford a significant economy in the number of necessary unknowns; on the other hand, being expressed as combination of Rao–Wilton–Glisson functions, reaction integrals are computed with optimum cost via fast methods. This is applied to reduce the cost of the optimization process used to design MS antennas based on spatially modulated reactance profiles. The authors support the method proposed, presenting criteria to define the entire-domain functions, considering the overall numerical complexity in an optimization framework, and providing a convergence analysis and the numerical results for holographic leaky-wave antennas, relevant in the MS context.