A high gain wideband circularly polarized antenna with asymmetric metasurface

An asymmetric‐metasurface based wideband circularly polarized (CP) microstrip antenna using a coaxial probe is proposed for L‐band applications. The antenna involves a stacked asymmetric‐metasurface, a radiating rectangular‐patch and a coaxial feed. An asymmetric‐metasurface is designed using rectangular unit cells and smaller size unit cells along one of the diagonal lines. The asymmetric‐metasurface is placed above a radiating rectangular‐patch with support of foam layer to achieve a wideband CP radiation. The measured performance of the prototype antenna achieves an impedance bandwidth (?10 dB return loss bandwidth) of 15.7% (1.58‐1.85 GHz) with CP bandwidth (3‐dB axial ratio) of 13% (1.58‐1.80 GHz) and gain of ≥9 dBic.     

Single‐layer high‐gain flat lens antenna based on the focusing gradient metasurface

A single‐layer transmitting focusing gradient metasurface (F‐GMS) has been proposed that can realize high gain increment at 10 GHz. The unit of F‐GMS is composed of two identical structures placed on the top and bottom of one dielectric layer, which can have high transmitting efficiencies that over 0.8 and achieve [0, 2π] phase range in X‐band. The F‐GMS can convert the spherical waves into plane waves. A patch antenna working at 10 GHz is positioned as the focus of the proposed F‐GMS as the feed source to develop an ultrathin flat lens antenna system. It achieves a simulated gain of 19.6 dBi which is 12.9 dB greater than that of the single patch antenna at 10 GHz. Lastly, the F‐GMS and the patch antenna are manufactured and then measured in an anechoic chamber. A good agreement was demonstrated between experimental and simulated results.     

A low scattering slot antenna based on broadband polarization conversion metasurface

An ultrawide band polarization conversion metasurface (PCM) is proposed to reduce the reflection of a slot antenna. The proposed PCM can convert a linearly polarized incident wave to the reflected wave with a 90° rotation. By arranging the PCM around the antenna symmetrically, an ideal phase cancelation is achieved. To verify the design, a metasurface‐slot antenna is simulated and measured to confirm the proposed PCM for a significant reduction of the reflection. Results show that the normal reflection of the proposed antenna at boresight is reduced more than 10 dB over an ultrawide band. In addition, 2 dB enhancement of the gain is achieved compared with a reference antenna which has the same dimensions. Meanwhile, the small influence is observed for the antenna radiation by introducing the PCM.     

High gain transmitarray antenna based on ultra‐thin metasurface

This article presents a bandwidth enhanced transmitarray (TA) antenna based on ultra‐thin metasurface (MS) for high gain operating at X‐band. The antenna consists of a three layers continuous flat structure and an aperture coupled microstrip antenna as the feed source. The relative phase shift of 360° is achieved by the unit cell design based on ultra‐thin MS, and the quasi‐spherical wave could be focused as plane wave when the wave goes through TA. The aperture coupled microstrip feed is designed with a bandwidth of 20.6%, and the bandwidth enhanced property of feed source will reduce the negative effect of elements mutual coupling on TA and increase the bandwidth of the TA antenna. The TA antenna gain increases from 8.25 to 18.98 dB and with a side lobe level of ?14.3 dB. Owing to the low‐profile and easy configuration, this kind of TA antenna has great potential, wireless communication.     

Compact ultrathin linear graded index metasurface lens for beam steering and gain enhancement

In this article, designing of a low‐profile planar linear graded index metasurface (LGIMS) lens is presented. A wide‐beam steerable high‐gain low‐profile antenna is designed by placing LGIMS over microstrip patch antenna radiator at an optimum height. Direction control of the radiation pattern of the microwave radiator by using amplitude and phase modulated metasurface is achieved. The measured peak gain of 13.50 dBi at an operating frequency of 10.08 GHz with progressively beam steering characteristic and progressive enhanced gain within a large conical region of apex angle 64°. The measured maximum gain tolerance of 2.43 dB with significantly reduced side lobe level is obtained by mechanically moving the ultrathin LGIMS lens along the negative parallel radiator axis. The mechanical movement of LGIMS lens over radiator results in to beam steering up to +32°. A maximum measured gain enhancement of 8.75 dB is achieved. The positive parallel radiator axis movement of LGIMS causes gradual broadside gain enhancement with maximum gain enhancement of 1.5 dB. The measured results are in good agreement with the simulated results.     

Two-dimensional broadband and wide angle scanning multi-beam antenna based on leaky-wave metasurface

In this article, a novel two-dimensional multi-beam antenna with a broad band and a wide angle scanning range is proposed. It is composed a leaky-wave metasurface (MTS) and a four-port feeding network with high isolation. The leaky-wave MTS formed by T-shaped slots is displayed as radiator and divided into four angular sectors, each one devoted to the formation of a beam in a given elevation plane. At every fixed frequency, the antenna can radiate multi beam in azimuth plane through exciting different ports. Also, multi-beam radiation with a broad band and a wide angle scanning range in the elevation plane is realized when fixed port is excited at different frequency. The antenna with overall size of 207 mm by 207 mm by 2.0 mm is fabricated on FR-4 substrate. The measured and simulated results show that the ?10 dB relative bandwidth is 30% (from 9.44 to 12.77 GHz). When different ports are excited at the same frequency, the azimuth of radiation beam is steered to 0°, 90°, 180°, and 270°. In addition, the beam-scanning range of the prototyped antenna is from 29° to 75° when the frequency sweeps in the range of 9.5–12.0 GHz. Also, the maximum radiation efficiency reaches to 31.1% and the measured peak gain within the scanning range is 12.29 dBi.     

A wideband low-radar cross section circularly polarized holographic antenna based on hybrid metasurface

A wideband low-radar cross section (RCS) circularly-polarized (CP) holographic antenna (HA) based on hybrid metasurface is proposed. The proposed HA is composed of a source antenna, a holographic metasurface (HM) and a hybrid metasurface. The HM is designed to transform a surface wave (SW) into a right-hand CP wave. A novel hybrid meatasurface is proposed, which is the main contribution in this paper. The hybrid metasurface consists of two kinds of frequency-selective absorbers (FSAs), both of which exhibit transmission characteristic for in-band waves so that a good radiation performance is maintained. For the out-of-band waves, HM and hybrid metasurface act together as an absorber within 3–11 GHz. On the contrary, they act as two kinds of reflective FSAs (RFSAs) with 180° ± 37° reflection phase difference within 17–24 GHz. Thus, the RCS is effectively reduced within 3–24 GHz. Finally, a reasonable agreement is obtained between measured and simulated results.     

Design of a compact wideband CP metasurface antenna

In this article, a new compact metasurface circularly polarized (CP) antenna is presented, where the rotating 45° periodic ellipse patch is used to achieve polarization conversion from linearly polarized to CP. The meta‐surface is composed of 4 × 4 ellipse patches with 45° rotation, which are etched on the top layer of upper substrate. A slot ground plane and a coplanar waveguide structure are printed on both sides of bottom substrate, and the bottom substrate is directly connected to the upper substrate, which can make the antenna profile lower. As demonstrated in this article, the presented antennas have good characteristics of excellent 3‐dB axial ratio bandwidth of 17.4% (5.25‐6.25 GHz), and wide 10‐dB impedance bandwidth of 20.6% (5.0‐6.15 GHz).     

Smart monopole antenna with pattern and frequency reconfiguration characteristics based on programmable metasurface

Metasurfaces having ultrathin and planar structure with sub‐wavelength unit cell, have recently gained significant potential for use thanks to their control capabilities over the electromagnetic waves from microwave to the visible range. The structure and the dimensions of the sub‐wavelength elements determine the electromagnetic properties, capabilities, and functionalities of the metasurfaces providing a full control of the reflected and transmitted fields and these metasurfaces are referred to as analog metasurfaces. When adjustability is added to the unit cells, programmable or digital metasurfaces are obtained, allowing us to take multiple unique functionality advantages controlled by external stimuli. In this study, we propose a metasurface structure, also known as 1‐bit coding metasurface, which is controlled depending on the “On/Off” state. The “On/Off” state is controlled by a computer program using genetical algorithm. Depending on the operating state, electromagnetic waves can be manipulated and different functionalities of the metasurfaces can be realized. The contribution and innovation of the study is the demonstration of the beam rotation, resonance frequency shift and radiation pattern reconfiguration properties of a simple monopole antenna by using controllable metasurface composed of T shaped resonator and circular patch with an operating frequency between 4.3 and 5.6 GHz.     

A new broadband circularly polarized antenna with a single‐layer metasurface

In this article, a new low‐profile broadband circularly polarized antenna with a single‐layer metasurface is designed. The metasurface is composed of 4 × 4 rotated rectangle‐loops. Compared to single rotated rectangle, introducing inner‐cut rectangle slot can increase the design flexibilities by changing this slot size for wider circularly polarized operating bandwidth and reduce the size of the antenna in same frequency. The proposed antenna has the advantages of a wide 3‐dB axial ratio bandwidth from 5.4 to 6.05 GHz and an excellent 10‐dB impedance bandwidth from 5 to 6.05 GHz.     

Low profile antenna based on a fractal shaped metasurface for public safety applications

In this article, design and analysis of a fractal shaped metasurface (FSMS) antenna for public safety applications is presented. It comprises of two layers, upper layer and lower layer. The upper layer has the metasurface (MS) and lower layer has the fractal inspired monopole antenna. MS is made up of Sierpinski Knopp fractal shaped unit cell, which is arranged in 4 × 6 layout to achieve miniaturization. Ansys Electronic Desktop tool is utilized for analyzing the performance of the MS antenna. The projected FSMS antenna is fabricated using FR4 dielectric material and experimented with the help of an anechoic chamber and Vector Network Analyzer (VNA). Results show that the FSMS antenna exhibits a bandwidth of 200 MHz and a gain of 1.56 dBi at 4.89 GHz. The results obtained in simulation and measurement are in good agreement. Consequently, the proposed antenna with a low profile of 0.43λ₀ × 0.43λ₀ × 0.03λ₀, where λ₀ is the free space wavelength at 4.89 GHz is well fit for public safety applications.     

宽频带高增益RFID微带天线阵设计

设计了一种宽频带高增益微带天线单元并组成了4元阵列。通过在普通矩形微带贴片加载2个对称切角、改变贴片表面电流分布实现天线单元的双频工作,调节切角尺寸使两个频点相互靠近融合,展宽频带。在此基础上确定合适的阵元间距,采用等副同向并联馈电,馈电网络由T型结功分器组成,并使用同轴探针馈电方式,实现天线阵列的设计。通过高频电磁结构仿真软件HFSS对天线进行仿真和优化,结果表明阵列天线性能良好。     

A compact configuration of semicircular metasurface loaded slot antenna for beam steering application

In this article, a compact beam steering antenna configuration is presented. The proposed structure comprises a semicircular radially gradient metasurface (SCRGM) and a slot antenna. This metasurface (MS) with the dimensions of 3.17λ₀² covers only half of the antenna aperture by placing it at a height of 0.16λ₀ from the slot antenna. The SCRGM is made up of four different semicircular regions, which introduce progressive phase delay to the impinging spherical electromagnetic waves from the slot antenna. The placement of the SCRGM tilts the main beam by 30° away from the normal direction. Furthermore, in‐plane movement (rotation and translation) of the SCRGM facilitates beam steering in the elevation plane (E‐plane) with the total scanning range of 60°. Moreover, in simulation, two SCRGMs are placed at both sides of antenna aperture to independently control the beam directions in both upper and lower hemispheres of the slot antenna. Due to the symmetry of the slot antenna, only one SCRGM is tested during the measurement process and the same outcome is expected for the other MS. Considerably small volume (0.50λ₀³) of the structure revealed compact antenna configuration. Moreover, independent control of the beam directions in both of the hemispheres makes proposed antenna a suitable candidate for various applications.     

Wideband printed slot antenna using Koch fractal metasurface structure

A novel wideband slot antenna with Koch fractal metasurface structure is presented in this letter. Using Koch metasurface as a slot edge, the proposed antenna obtains excellent performance in bandwidth. For optimal bandwidth, optimization is done for both iteration angle (IA) and iteration factor (IF) at each iteration order (IO). The measured results show that the impedance bandwidth of the optimized antenna can reach about 1.75 octaves (1.45‐4.86 GHz) for VSWR ≤ 2. In addition, stable radiation patterns are observed over the whole operating band of the proposed antenna.     

Wideband beam‐steerable configuration of metasurface loaded slot antenna

In this article, a wideband two dimensional (2D) beam‐steerable antenna structure is presented. The proposed structure is based on a radially gradient hybrid metasurface (RGHMS) illuminated through a slot antenna. The half aperture of the RGHMS comprises of a gradient phase profile topology, while its other half aperture consists of a constant phase profile configuration. The slot antenna possessing the bidirectional radiation pattern is printed on a relatively thin substrate, which operates over a wide bandwidth of 1420 MHz (15.10%). The placement of RGHMS tilts the main beam of slot antenna by 15° away from normal direction. Further, in‐plane movement of MS provides beam steering in both elevation and azimuth planes, with a conical region of an apex angle of 30°. Apart from the beam steering capability, the placement of RGHMS in front of slot antenna also enhances the overall bandwidth and gain by 360 MHz and 5 dB, respectively. Thus, a wide band beam steering configuration with the impedance bandwidth of 1780 MHz (18.85%) is obtained. In order to investigate the frequency dependent beam tilting capability of the RGHMS in the elevation plane, a detailed analysis is carried out using the principle of refraction.     

Analysis of one wide‐band and high gain patch microstrip antenna using the FDTD method

We present results of a recent investigation into a wide‐band and high gain patch microstrip antenna using the finite‐difference time‐domain (FDTD) method. The substrate–superstrate resonance technique was used to increase the antenna element gain. An aperture‐coupled rectangular patch microstrip antenna with two superstrate layers was designed, and the effect of the finite ground plane on the gain of the antenna element was analyzed. The antenna was fabricated and tested. The measured results are presented in comparison with the simulated ones. ©1999 John Wiley & Sons, Inc. Int J RF and Microwave CAE 9: 468–473, 1999     

Compact high gain half‐mode substrate integrated waveguide cavity antenna using hybrid mode

In this article, a compact fully planar high gain antenna based on half‐mode substrate integrated waveguide (HMSIW) cavity is presented. The design uses a novel configuration of HMSIW cavity with high length to width ratio along with tapered open edge and a pair of slot stub. The high length to width ratio of the cavity helps to excite closely spaced multiple TE^y_m10 cavity modes within comparatively smaller footprint due to use of the HMSIW cavity. These modes combine to give hybrid mode resonance in the cavity which helps to generate a narrow beam high gain radiation pattern of the antenna. The size of the proposed antenna is further reduced and a pair of slot stub is put along the sidewall of the cavity which helps to sustain similar hybrid mode field distribution within much smaller dimension. A size reduction of 76.7% is achieved in the proposed design configuration without degrading much of the gain performance. The proposed antenna resonates at 9.8 GHz with a gain of 7.9 dBi which is much higher than other reported HMSIW cavity antenna. The proposed antenna may find application in point to point communication, short range radar in X band.     

High‐gain waveguide slot antenna using simple parasitic patch's cover

In this article, a way based on using miniature patch cells has been proposed to increase gain and bandwidth of the waveguide slot antenna. In the presented approach, an array of 3 × 3 metal patches has been used as superstrate to create Fabry Perot theorem resonance cavity. The proposed high ‐ gain and simple antenna is composed of a conventional waveguide slot antenna with an extended broad wall, and an array of parasitic patches which are symmetrically placed over slot at a distance of about free ‐ space half wavelength. The slot has been created on a rectangular waveguide WR90 with 22.86 mm × 10.16 mm × 52.5 mm dimension, also extended wall dimension is 2λ₀ (67.5 mm) × 3λ₀ (107 mm). It has been shown that the proposed structure compared with the conventional waveguide slot antenna improves antenna peak gain from 6.5 to 16.5 dBi and, in the same time, antenna bandwidth from 11% to around 16.2%. More important advantage of the proposed antenna is that unlike to other Fabry Perot antenna with the same gain, there is not any dielectric material in the proposed structure. A prototype antenna was simulated, fabricated, and measured for verification.     

Broadband compact CPW‐fed metasurface antenna for SAR‐based portable imaging system

A broadband and compact coplanar waveguide (CPW) coupled‐fed metasurface (MS)‐based antenna for C‐band synthetic aperture radar (SAR) imaging application is proposed in this article, which is consisted of 16 uniform periodic square patches performed as radiators. The CPW feeding structure gives two following functions: (1) It excites an aperture coupling slot structure underneath the center of MS patch array. (2) It acts as a ground plane for the metasurface patch units. Different slots were investigated and eventually an hourglass‐shaped slot is applied to enhance bandwidth for imaging applications. A prototype with a dimension of 60 × 60 × 1.524 mm³ (1.1λ₀ × 1.1λ₀ × 0.03λ₀) operating at the center frequency 5.5 GHz (f₀) has been fabricated and measured to verify the design principle. This antenna has a measured impedance bandwidth of 12.4% from 5.14 to 5.82 GHz, a peak gain of 9.2 dBi and averaged gain of 7.2 dBi at broadside radiation. Microwave imaging experiments using the proposed antenna have been carried out and a good performance is achieved.     

Wideband high gain conical dielectric resonator antenna: An experimental study of superstrate and reflector

A physically feasible new hybrid geometry for gain improvement with wideband characteristics is designed and validated experimentally in a conical shaped dielectric resonator antenna (DRA). It comprises of one superstrate and one reflector, with simple slot coupling technique for excitation. The reflector beneath the ground plane mainly accountable for significant gain improvement (～109%) by reducing the back radiation, whereas the superstrate dedicates for maintaining wideband (12.65%). The demonstrated result shows S ₁₁ < ?10 dB band between 7.4 GHz and 8.4 GHz, with 11.25 dBi peak gain, which are well matched with their simulated counter parts. It also gives high co‐pol to cross‐pol difference (～40 dB) in broadside direction. This new geometry can be eligible for X‐band applications as well can usher the DRA researchers for further innovations.