一种采用吸波透波超表面的天线RCS宽带减缩新方法

设计了一款具有吸波/透波双重特性的超表面,并将其用于微带天线的覆层,实现天线雷达散射截面(radar cross section, RCS)的宽带减缩. 将传统的结构性吸波材料金属单元用氮化钽材料置换,提升了吸波带宽. 同时,将吸波材料与频率选择表面相结合,实现了覆层对于不同来波方向的电磁波分别呈现吸波/透波两种截然不同的电磁特性. 将覆层置于天线上方,当天线工作时,天线辐射的电磁波可以完美穿过覆层,因此对于天线的辐射特性不会造成影响. 当雷达波照射至天线时,覆层所呈现的宽带吸波特性可最大程度降低天线的RCS. 仿真结果表明:使用本文所设计的吸波/透波超表面作为天线覆层时,天线的辐射特性几乎未发生变化;而天线的单站RCS最大减缩量可达20 dB以上,减缩带宽可达5～19 GHz;同时,天线的单、双站RCS在较宽的角度范围内也得到明显的缩减.     

Coupling Reduction Between Dipole Antenna Elements by Using a Planar Meta-Surface

The mutual coupling between dipole antenna array elements using a planar meta-surface as superstrate is experimentally investigated. The meta-surface is based on grids of short metal strips and continuous wires. A comparison between the mutual coupling when the dipoles are radiating in free space and in presence of the superstrate is presented. On average, between 3 to 14 dB reduction of the mutual coupling is achieved when the superstrate is used. The effect of the mutual coupling on the radiation performance of the array is studied by spherical near-field measurements of the radiation pattern when one driven dipole is fed and the others are matched with 50 $Omega$ loads. The back-projected field on the aperture and on the E-plane is shown.      

A High‐Gain Microstrip Patch Array Antenna Using a Superstrate Layer

A dielectric superstrate layer above a microstrip patch antenna has remarkable effects on its gain and resonant characteristics. This paper experimentally investigates the effect of a superstrate layer for high gain on microstrip patch antennas. We measured the gain of antennas with and without a superstrate and found that the gain of a single patch with a superstrate was enhanced by about 4 dBi over the one without a superstrate at 12 GHz. The impedance bandwidths of a single patch with and without a superstrate for VSWR < 2 were above 11%. The designed 2×8 array antenna using a superstrate had a high gain of over 22.5 dB and a wide impedance bandwidth of over 17%.     

Radiation of High-Gain Cavity-Backed Slot Antennas Through a Two-Layer Superstrate

The radiation of cavity-backed slot (CBS) antennas through a two-layer superstrate is studied in this paper. A novel transmission-line model is proposed to explain the gain-enhancement effect of the superstrate on cavity-backed slot antennas. Experimental result showed that a single cavity-backed slot antenna can achieve a high gain of 16.7 dBi through a properly designed superstrate, and this gain-enhancement property is valid for array configurations, as well. A rotationally arranged four-slot array, covered by the superstrate, is also investigated, to demonstrate that good circular polarization and high gain can be obtained from the superstrate-covered slot antennas.     

使用非均匀特异媒质覆层的高增益谐振腔天线

采用非均匀特异媒质覆层,设计了一种具有高增益特性的新型谐振腔天线。该谐振腔天线采用矩形微带贴片天线作为辐射单元,安装在金属谐振腔内,其谐振频率为10 GHz。为提高天线增益,将腔表面安装蚀刻在微带基板上,由周期性单元组成特异媒质覆层。迥异于常规的单元尺寸均匀一致特异媒质覆层,本文研制的非均匀特异媒质覆层包含9×9个矩形单元,单元大小渐变。仿真表明,与常规均匀特异媒质覆层相比,该新颖的非均匀特异媒质覆层相当大程度提升了天线定向辐射性能：天线增益提高1.2 dB(从20.3 dBi增加到21.5 dBi),天线的旁瓣得到了抑制,主旁瓣比下降5 dB;同时,天线谐振频率和阻抗带宽等其他性能基本保持不变。     

Design and performance of an ultrawide-band ceramic-loaded slot spiral

The miniaturization of a broadband square slot spiral antenna is proposed using high-contrast (/spl epsiv//sub r/>30) dielectric materials. A previously developed circular slot spiral antenna is the starting point of the design. This spiral is first modified in terms of its feed and termination to facilitate the dielectric loading of the antenna by means of a superstrate. The subsequently placed superstrate is also modified by tapering its thickness to improve impedance matching. Several measurements were carried out using square spiral apertures having diameters of 2' and 6', respectively. It is demonstrated that the ceramic loading of a 2' spiral with an /spl epsiv//sub r/=90 shifts the initial operating frequency by nearly 320 MHz down to 564 MHz representing a size reduction of 36%. Additionally, a 6' aperture loaded with a superstrate having /spl epsiv//sub r/=30 is shown to operate down to 270 MHz corresponding to a size reduction of 18%.     

Superstrate loading effects on the circular polarization andcrosspolarization characteristics of a rectangular microstrip patchantenna

The authors present the superstrate loading effect on a circularly polarized rectangular microstrip antenna. The design parameters of the superstrate-loading microstrip antenna for achieving circular polarization at the main-beam direction are discussed. The circular polarization property in the entire main-beam region is also analyzed. Next, the crosspolarization characteristics of a rectangular patch antenna due to the superstrate loading are studied. A great dependence of the copolarized and crosspolarized radiations on the superstrate permittivity and thickness is observed     

Some studies on two-layer electromagnetically coupled microstrip antenna with dielectric cover

Experimental investigations are carried out for two configurations, namely a driven hexagonal patch and an electromagnetically coupled microstrip antenna (EMCA), with different dielectric superstrates. Superstrate loading of the antenna is found to cause a considerable shift in the resonance frequency. The driven patch with superstrate behaves as an RL network. The maximum bandwidth of 6.21% is observed for the EMCA with a bakelite superstrate when the dielectric constant of the superstrate and the substrate of the antenna are equal.     

Polarisation referencing in refractometry using fibre to planarwaveguide couplers incorporating thin metal layers

The wavelength response of fibre to metal clad planar waveguide couplers has been investigated as a function of superstrate index. The TE resonance wavelengths remain fixed with superstrate index variation while the TM resonance position demonstrates good superstrate index sensitivity. Such a technique may be used for polarisation referencing and temperature compensation in refractometry     

High-gain compact circularly polarised microstrip antenna

Design of a high gain, small microstrip antenna with circular polarisation (CP) radiation is demonstrated. The small size of the microstrip antenna results from both the high-permittivity superstrate loading and the slits cut in the patch. In addition, the antenna gain is enhanced by setting the superstrate thickness at about one-quarter of the wavelength in the superstrate layer. A typical design with a 30%, decrease in antenna size and a 5.2 dB increase in antenna gain, as compared to the conventional CP design, is presented and analysed     

Fundamental superstrate (cover) effects on printed circuit antennas

The fundamental effects of superstrate (cover) materials on printed circuits antennas are investigated. Substrate-superstrate resonance conditions are established which maximize antenna gain, radiation resistance, and radiation efficiency. Criteria are determined for material properties and dimensions for which surface waves are eliminated and a radiation efficiency due to substrate-superstrate effects ofe_{s} = 100percent is obtained. Criteria for nearly omnidirectionalbar{H}-plane patterns and nearly omnidirctionalbar{E}-plane patterns are presented. Finally, a general criterion is given for choosing a superstrate to optimize efficiency for the important case of nonmagnetic layers with the antenna at the interface.     

Experimental study of circularly polarised microstrip antennas loaded with superstrate

The loading effects of the superstrate with various thickness on the circular polarisation (CP) performances of a cross-slot-coupled microstrip antenna are first investigated. Then, for improving the shifted centre frequency, the bad impedance matching, and the increased axial ratio, which are due to the superstrate effects, the key dimensions of the loaded antenna are adjusted to regain or even enhance the original unloaded CP performances. From the obtained experimental results, it is found that the CP bandwidth of the loaded antenna can be increased when the thickness of the superstrate is properly selected.     

Triple Band Circular Patch Microstrip Antenna with Superstrate

A novel compact triple band slit cut circular patch antenna with superstrate is proposed; slits on the patch provide additional resonances. The superstrate (cover) of dielectric layer provides protection to printed circuit antenna from environmental hazards due to abnormal weather conditions. The slits add two resonances in the resonance of a circular patch to achieve triple band antenna for multi services. The dielectric superstrate or cover above the microstrip patch causes the change in fringing fields between the patch and ground plane. The change in fringing field is accounted to calculate the effective relative permittivity. The effective permittivity is considered to evaluate the changes in resonance frequency due to superstrate. The various parameters of the antenna have been investigated and the antenna is simulated on Ansoft’s HFSS software simulator. A prototype of antenna is fabricated to confirm the return loss by measurement using the Agilent Technologies’ N5230A PNA-L Network Analyzer. The proposed structure with superstrate possess triple band characteristics and provides protection from environmental hazards. The resonating frequencies of the bands are 7.3, 8.7 and 10.3 GHz. The analytical results are found in good agreement with the simulated results obtained by Ansoft’s HFSS and further confirmed by measurement. Antenna is worth for X band operations such as remote sensing, WPAN and military satellite communication and vehicular applications.     

Analysis of Antenna Gain Enhancement with a New Planar Metamaterial Superstrate: an Effective Medium and a Fabry-Pérot Resonance Approach

We have compared gain enhancement behavior of patch and horn antennas from two different points of view: namely, effective medium analysis and a Fabry-Pérot cavity resonance approach. To examine how a near-zero refractive index (n) affects the performance of antennas, we designed a new planar metamaterial (MTM) superstrate, which can produce negative, zero, and positive values of n at around 2 GHz. We placed the MTM superstrate very close to the patch and horn antennas to see whether an n value that is effectively near zero can collimate antenna beams and increase antenna gain, which provided opposite gain behavior for the two antennas. To explain the dissimilar enhancement in the gain of the patch and horn antennas, we retrieved constitutive parameters from the proposed MTM superstrate and discussed the effect of various incidence angles upon the superstrate. In addition, to increase the gain further, we examined appropriate resonant heights between the antennas and the superstrate. Consequently, with the help of Fabry-Pérot cavity resonance, we obtained relatively high antenna gain. Moreover, the results of the prediction are in good agreement with the results of the measurement.     

Investigation Into the Effects of the Patch-Type FSS Superstrate on the High-Gain Cavity Resonance Antenna Design

Results of modeling, design, simulation and fabrication are presented for a high-gain cavity resonance antenna (CRA), employing highly-reflective patch-type superstrates. In order to determine the resonant conditions, the antenna is first analyzed using the transverse equivalent network (TEN) model, as well as the well known simple ray-tracing method. Prior to that, a highly-reflective patch-type frequency selective surface (FSS) is designed in order to be employed as the superstrate layer of the CRA. Next, a 2.5-D full-wave analysis software package, based on the method of moments (ANSOFT Designer v4.0), is utilized to analyze the antenna structure. Using this full-wave analyzer, the input impedance properties of an actual antenna are investigated as well. Then, a 3-D full-wave analyzer, based on the finite element method (ANSOFT HFSS), is used to extract the directivity and radiation patterns of the CRA, taking into account the finiteness of the substrate, superstrate and ground plane. Some previously unaddressed issues, such as the effects of the FSS superstrate on the input impedance characteristics of the probe-fed microstrip patch antenna, acting as the excitation source of the CRA are also studied. The effects of the highly-reflective FSS superstrate size on the CRA directivity, and explicitly its aperture efficiency, are investigated as well. A comparative study is also performed between CRAs with patch-type FSS and high permittivity dielectric superstrates. Measurement results are provided to support the modelings and simulations.      

On the coupling characteristics of coplanar waveguides andmicrostrip lines to multilayer dielectric media

The spectral-domain technique is utilized to optimize the coupling of coplanar waveguides and microstrip lines to lossy dielectric media. It is shown that to enhance the coupling, higher frequencies should be used, the dielectric constant of the substrate should be small (∈=2.56), and the width of the center conductor and gaps should be as large as possible. The dielectric constant of the superstrate should be low if a leaky-wave type of coupling is desired or large if a strong coupling by the transverse-field components is desired. It is shown that the quasi-static TEM and TM₀ modes will be excited if a superstrate is present between a high dielectric lossy media and the coplanar waveguide     

Substrate radiation losses in GaAs heterostructure lasers

Double-heterostructure (DH) diode lasers with a thin Ga1-xAlxAs layer between the active GaAs region and the GaAs substrate or superstrate are analyzed. In these devices power flows through the thin Ga1-xAlxAs layer and is radiated into the substrate or superstrate. Three methods for computing the laser thresholds are developed and compared. The first is an analytic perturbation technique, which yields accurate results in many cases of practical interest. The second and third are rapidly convergent numerical iteration techniques. The former utilizes overlap integrals to compute absorption losses and thresholds; the latter includes all losses and gains directly in the formulation. We show that conventional DH diode lasers can be designed with thick active GaAs layers and still achieve lowest order TE-mode operation. These devices will produce better collimated, higher power output beams than do similar devices with thinner active regions. Transverse-mode control is achieved because all higher order modes have increased penetration through the thin Ga1-xAlxAs , and therefore exhibit inereased radiation losses into the substrate or superstrate. A design example is included in which it is shown that with proper choice of the Ga1-xAlxAs-layer thickness the TE0-mode threshold increases by 5 percent compared with a 110-percent increase in the TE1threshold. These results are virtually independent of the substrate power-absorption coefficient. Threshold current densities are computed for a set of diodes studied experimentally by Casey and Panish and the results are shown to be in excellent agreement.     

EBG Superstrate Array Configuration for the WAAS Space Segment

Two different electromagnetic bandgap (EBG) superstrate array antenna configurations, intended for the Wide Area Augmentation Service space segment, are presented in this paper. The described antenna configurations take advantage of the directivity enhancement produced by a semireflective sheet placed parallel to a metallic ground plane. The first design presented is realized using a 2$,times,$ 2 circularly polarized (CP) patch array illuminating an EBG superstrate composed of a square pattern of circular holes etched in a thin metallic sheet. The second design consists of a 2$,times,$ 2 CP helix array feeding a hexagonal pattern of holes etched into a metallic EBG superstrate. Both configurations have been designed, breadboarded, and measured, and excellent agreement between simulations and measurements has been recorded. The accurate control of the antenna pattern phase center variation with both the frequency and the antenna field of view, necessary for the intended navigation antenna application, has been the principal challenge of this work. The EBG technology designs presented here are simpler than conventional navigation antennas and can lead to cost reduction, beamforming network simplification, and height reduction while offering similar radio-frequency performances to equivalent products realized in conventional technology.      

Ferrite-filled slot array antenna with superstrate

Radiation from a ferrite-filled slot array antenna with a superstrate is investigated. The Fourier transform and mode matching are utilised to obtain a rigorous solution. The radiation patterns of a ferrite-filled slot array antenna with a superstrate are measured at 10.05 GHz to confirm good agreement with computational results.     

Analysis of Annular Ring Microstrip Antenna with Air Gap and Uniaxial Substrate Superstrate Layers

Analysis of superstrate loaded, air gap tuned annular ring microstrip antenna is performed and effects of air gap tuning on the resonant frequency are investigated. Results obtained indicate that due to air gap tuning, resonant frequency can be incrementally or decrementally changed depending on the adjustment of anisotropy ratio of substrate and superstrate layers. Results can be used to obtain tunable, wideband antenna operation.