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.     

A small microstrip patch antenna with a convenient tuning option

The paper addresses two aspects of resonant microstrip patch antennas, namely, miniaturization and resonant frequency tuning. First, a patch geometry which allows a controllable size reduction over a limited range is presented. The basic shape is circular with slits cut into it. Modification of the slit geometry leads to both linear as well as circular polarized (CP) operation. Second, the use of another patch of a specific shape as a superstrate layer in a stacked configuration allows tuning over a relatively large frequency range as compared to the patch bandwidth. Tuning is accomplished by a simple rotation of the superstrate layer. The use of another superstrate layer allows tunable CP operation. Details on the antenna characteristics have been worked out for two examples, and computations have been compared with measurements where possible. Some design guidelines have also been included     

The absorption and coupling of an electromagnetic wave incident ona microstrip circuit with superstrate

The absorption of an electromagnetic wave incident on a microstrip circuit covered with a dielectric layer is studied. The exact analytical expression for the plane-wave reflection coefficient at the air-superstrate interface of a four-layer model for a superstrate-loaded microstrip circuit is given. Numerical results illustrating the power absorption by the microstrip circuit and the electric and magnetic fields on the surface of the circuit as a function of wave frequency, superstrate thickness, superstrate permittivity, and incident angle are presented. It is found that the power absorption by the circuit at resonant frequencies increases with increasing superstrate permittivity. Higher superstrate thickness and permittivity can both cause more resonant power absorption peaks in the frequency spectrum. Significant intensities of electric or magnetic fields can also exist on the surface of the circuit for almost all the frequencies, which may couple to the circuit and cause malfunctions or interference. Details of the numerical results are presented     

Resonant Meta-Surface Superstrate for Single and Multifrequency Dipole Antenna Arrays

The design of a multifrequency dipole antenna array based on a resonant meta-surface superstrate is proposed. The behavior of a single element that is closely placed to a meta-surface is experimentally investigated. The proposed meta-surface is based on resonating unit cells formed by capacitively loaded strips and split ring resonators. By tuning a dipole antenna to the pass band of the meta-surface, the physical area is effectively illuminated enhancing the radiation performance. The gain, radiation efficiency and effective area values of the whole configuration are compared to the ones obtained with a single dipole without superstrate. Radiation efficiency values for the proposed configuration of more than 80% and gain values of more than 4.5 plusmn 1 dB are obtained. Based on this configuration, simulated results of a multifrequency antenna array are presented. Distinctive features of this configuration are high isolation between elements (20 dB for a distance of lambda₀/4), and low back radiation.     

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.     

等离子体在强电磁脉冲防护中的应用

为了提高屏蔽腔对强电磁脉冲的屏蔽效能,分析了在屏蔽腔中引入等离子体的理论基础,建立了一种加载等离子体的双层屏蔽腔模型,采用时域有限差分法计算了强电磁脉冲耦合进入双层屏蔽腔的耦合系数。计算结果表明:加载等离子体的双层屏蔽腔可使强电磁脉冲耦合进入腔体的能量大大降低,在2～14GHz内耦合系数降低了近30dB,即使屏蔽效能也提高了近30dB,为新的屏蔽腔设计提供了重要的理论依据。     

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。     

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%.     

The RCS of a rectangular microstrip patch in asubstrate-superstrate geometry

A general scattering formula is derived for an arbitrary resonant conductive body within a layered medium, which shows that the body radar cross section (RCS) is directly related to the radiation efficiency of the body. The radar cross section of a rectangular microstrip patch antenna in a lossy substrate-superstrate configuration is then investigated as a specific case. Results are presented to show the effects of loss in the substrate, a lossless superstrate, and a lossy superstrate     

Resonant characteristics of aperture type FSS and its application in directivity improvement of microstrip antenna

In this paper, we propose an aperture type frequency selective surface (FSS) by employing an array of 12 × 12 unit cell elements and its resonant characteristics is analyzed. A resonant cavity antenna is then formed by the ground plane substrate and the FSS superstrate. The high reflective behavior of the proposed FSS at an offset of the resonance is then utilized for improving the performance of this cavity antenna. The impedance bandwidth and directivity are improved up to 0.66 GHz and 8.95 dBi, simultaneously at an optimum gap of 17.6 mm between the antenna substrate and FSS superstrate. For validation purpose, prototypes of both patch antenna and FSS, are fabricated and characterized. A fairly good agreement is achieved between the measured and simulated results.     

A Proposal of a New Dielectric Resonator Construction for MIC's

A compact and high-temperature-stable dielectric resonator having no shielding metal walls nor a conventional frequency tuning screw is described. This resonator consists of a high epsilon/sub r/ dielectric resonator element mounted on a low-loss dielectric mount, a dielectric disk with thin metal film fixed on the resonator element, and a microstrip line substrate on which to mount the constituents. The resonant frequency tuning is made by trimming the metal film on the disk. The TE/sub 01delta/ -mode resonant frequencies are analyzed through dielectric waveguide model application. Less than 1-percent analytical error is presented in comparison with the experimental data for a practical resonator. The frequency tuning limit by metal film trimming is about 7 percent. The unfoaded Q value of 2700 at 8.8 GHz and a 4.4-ppm/deg frequency temperature coefficient are obtained.     

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.      

Radiation of a rectangular microstrip patch antenna covered with a dielectric layer

The effect of a protecting dielectric superstrate on the radiation pattern of a rectangular microstrip patch antenna is investigated theoretically. The analysis approach is based on the spectral-domain method of moments in conjunction with the stationary phase method. A new concise expression is derived for computing the radiation electric field. The validity of the solution is tested by comparing the computed results with the experimental data. At higher superstrate thicknesses, numerical results indicate that the radiation pattern drastically changes into three lobes. The resonant frequency, on the other hand, increases with the increase of the thickness of the dielectric cover.     

Resonance in a superstrate-loaded rectangular microstrip structure

The complex resonant frequency of a superstrate-loaded rectangular microstrip structure is investigated. The study is performed by using a full-wave analysis and Galerkin's moment method. The numerical convergence using sinusoidal basis functions, with and without considering the edge singularity to expand the unknown surface current distribution on the rectangular patch, is discussed. Numerical results for the effects of superstrate permittivity and thickness on the complex resonant frequency of the rectangular microstrip structure are also presented     

Resonant frequency of uncovered and covered rectangular microstrippatch using modified Wolff model

A new model, called the modified Wolff model (MWM), is proposed to calculate the resonant frequency of a rectangular open microstrip patch, a patch with a dielectric superstrate and a patch inside a shielded enclosure. The model has also been applied to calculate resonant frequencies of higher-order modes. The dependence of resonant frequency on the various parameters and its accuracy are discussed using the MWM. Results obtained from MWM follow very closely the results from various forms of full-wave analysis, and in almost all cases they are within 0.5% of published experimental results for the fundamental mode and within 1.7% for higher-order modes. The method is computationally fast and efficient even on a desktop computer. The method could be used for other patches like circular, hexagonal and equilateral triangle     

Ferrite‐based wideband circularly polarized microstrip antenna design

In this paper, a wideband, circularly polarized patch antenna is proposed that leverages the unidirectional resonant modes of a circular patch mounted on top of a grounded dielectric‐ferrite substrate. The proposed antenna is fed via the proximity coupling method and several parasitically coupled patches are placed on a dielectric superstrate to enhance the impedance bandwidth of the antenna. The resonant modes of the structure rotate only in the clockwise or counter clockwise directions. In the frequency range where the effective permeability of the ferrite layer is negative, the resonance frequencies of these modes differ significantly, which produces a large axial ratio (AR) bandwidth. For the proposed antenna, the numerical results show the 10 dB impedance bandwidth to be around 44% and the 3 dB axial ratio bandwidth to be higher than 64%.     

Shielding properties of an ensemble of thin, infinitely long,parallel wires over a lossy half space

A determination of the total electric field produced by an ensemble of thin, infinitely long, parallel wire scatterers over a flat lossy half space illuminated by a plane wave whose polarization is parallel to both the wires and the interface is presented. By invoking the thin wire idealization, a matrix equation is obtained for determining the currents on each wire, from which the total electric field is obtained. Several plots are given to show how the wires' radii, the earth's conductivity, the incident angle, and the total number of wires affect the shielding for a semicircular shell. In many cases, it is demonstrated that the shielding effectiveness can be as much as 70 dB; for other cases, when the structure is of resonant dimensions, the shielding can be degraded to 20 dB. It is also shown that a wire grid model can give shielding results similar to those of a continuous perfectly conducting structure of similar dimensions     

Polarization properties of a fiber to planar waveguide couplerincorporating a thin metal layer

A fiber to planar waveguide coupling structure incorporating a thin metal layer is described. The resonant wavelengths for the TM polarization were found to be highly sensitive to the refractive index of the superstrate material while those for the TE polarization were unaffected. A theoretical model for the multilayer structure was developed on the basis of a matrix method approach and a preliminary analysis of the resonance shift phenomena for the TM mode shows good agreement with experiment     

高增益高效率的Fabry-Perot谐振腔天线研究

提出了一种采用非均匀频率选择表面（frequency selective surface, FSS）盖板以及非均匀电磁带隙（electromagnetic band gap, EBG）结构反射地板的高增益Fabry-Perot（F-P）谐振腔天线. 基于漏波理论模型,针对大口径F-P谐振腔天线设计非均匀的FSS盖板和EBG反射地板,控制衰减常数α和相位常数β,改善了口径场上幅度相位分布的均匀性,并抑制了非谐振频率时天线辐射性能的恶化,实现高增益和高口径效率的同时,保证了天线的工作带宽. 所提出的圆形F-P谐振腔天线直径为6.6λ₀,仿真增益为24.6 dBi,口径效率达67.9%,阻抗带宽为4.1%,3 dB增益带宽为3.7%;实测增益为23.9 dBi,口径效率达56.9%. 由于对口径场均匀性的设计,该天线克服了传统F-P谐振腔天线的口径效率和增益间的相互限制.     

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.