The effect of a dielectric cover on the current distribution and input impedance of printed dipoles

The effect of the thickness and relative permittivily of a dielectric cover on a printed microstrip dipole has been analyzed. It is shown that the current distribution and the input impedance are, in general, very sensitive to variations of the cover parameters. For a dielectric plate with a constant thickness the dipole resonant length decreases substantially with an increase of the relative permittivity. Because of the limited bandwidth presented by single-element microstrip antennas the effects of the dielectric cover on the design of these antennas have to be carefully considered. For the calculation of the current distribution, the Hertz vector potential associated with the problem was determined for an element of current located in a stratified medium with four layers. Pocklington's integral equation was solved for the currents, using Galerkin's method with piecewise-sinusoidal expansion and weighting functions.     

介质覆盖矩形微带天线的理论与实验

本文研究了介质覆盖矩形微带天线的特性，精确的谱域全波分析方法被扩展到这类天线的分析中，给出了理论计算公式，探讨了介质覆盖层和对矩形微带天线的驻波比的影响，实验结果证实了理论计算的正确性。     

Calculation of the input impedance of a strip loop antenna located on a dielectric cylinder

A method for calculating the input impedance of a loop antenna (LA) located on a dielectric cylinder is developed. The integral equation (IE) for the unknown function of the current density distribution on the LA surface is obtained. A numerical method for the IE solution is described. An approximate formula for calculation of the LA input impedance is proposed. Plots of the input impedance on the LA length are given.     

An impedance sheet approximation for thin dielectric shells

An approximate equivalence between an impedance loaded surface and a thin dielectric shell is given. This approximation is used to compute the backscattering from a thin circular dielectric tube and the results are compared to the exact solution. Computations for backscattering from a thin dielectric cone-sphere and resonant wire loop inside of a thin dielectric cylinder are also given as further illustrations of the method.     

Microwave measurement of temperature and current dependences ofsurface impedance for high-Tc superconductors

Perturbation formulas for TE₀₁₁-mode dielectric rod resonator and for a TE₀₁₁-mode circular cavity resonator are derived to determine the surface impedance Z_s of superconductors from measured values of resonant frequencies and unloaded Q. The relation between the maximum surface current density of a superconductor, J_s, and output power from a signal generator is derived. On the basis of these analytical results, a measurement technique is proposed to evaluate the temperature and J_s dependencies of Z_s for superconductors. The measured results of the temperature dependence of Z_s for YBCO and copper plates are presented. From these results, it is verified that the dielectric resonator is suitable for measuring the surface reactance for YBCO. From these Z_s values the temperature dependences of the skin depth and the penetration depth and those of the complex conductivity are obtained on the basis of the two-fluid model. These measured values agree well with the theoretical curves     

Resonant Frequency of a TE//sub 01delta//spl deg/ Dielectric Resonator

The resonant frequency of a TE/sub 01delta//spl deg/ dielectric resonator was obtained by assuming a cylindrical surface containing the circumference of a dielectric resonator as a magnetic wall. In such a method, the error was less than 10 percent. In this short paper, the resonant frequency is obtained by a variational method, where the surface impedance is variated from a infinite value. The theoretical value of a resonant frequency has a good agreement with our experimental result with an error less than 1 percent.     

Calculation of the input impedance of a stripline dipole conformally situated on a dielectric cylinder

A method for calculation of the input impedance of a stripline dipole (SD) conformally situated on a dielectric cylinder is developed. A singular integral equation (SIE) for the unknown current density distribution function on the SD surface is obtained. A numerical method for solution of this SIE is described. The dependence of the input impedance on the SD length is obtained.     

Microwave surface impedances of BCS superconducting thin films

The microwave propagation-dominated problem in the multilayer structure made of a BCS superconducting film and a dielectric substrate is investigated theoretically by using the modified two-fluid model and transmission line theory. The effective microwave surface impedances are studied as functions of temperature, frequency, and film thickness, as well as substrate thickness. Special attention is paid to the substrate resonance phenomenon in the resonant structure. The influence of BCS coherence effects on surface impedance and resonant behavior is clearly demonstrated. The resonant effect in the stack structure is well interpreted with the help of the transverse resonance technique in the microwave theory     

Theory and experiment of a coaxial probe fed hemisphericaldielectric resonator antenna

A hemispherical dielectric resonator antenna fed by a coaxial probe is studied both theoretically and experimentally. The Green's function for the evaluation of the input impedance is derived rigorously and expressed in a form convenient for numerical computations. The method of moments is used to obtain the probe current from which the input impedance of the DR antenna is calculated. Both delta gap and magnetic frill source models are considered. Moreover, the results using a reduced kernel as well as the exact kernel are presented. Both entire basis (EB) and piecewise sinusoidal (PWS) expansion modes are used and the results are compared. The effects of the probe length, feed position, and dielectric constant on the input impedance are discussed. Finally, the theoretical radiation patterns for the first three resonant modes (TE₁₁₁, TM₁₀₁, and TE₂₂₁) of the DR antenna are presented     

The impedance properties of dielectric-covered narrow radiating slots in the broad face of a rectangular waveguide

An extension of Oliner's theory is used to predict the impedance of slots with dielectric coatings. Theoretical curves are presented which show the change in impedance as a function of dielectric constant, dielectric losses, and dielectric thickness. The effect of a dielectric or plasma upon the resonant frequency is also included. The agreement with experimental dielectric-covered slot data justifies the extension of Oliner's theory.     

A New Compact Microstrip-Fed Dual-Band Coplanar Antenna for WLAN Applications

A novel compact microstrip fed dual-band coplanar antenna for wireless local area network is presented. The antenna comprises of a rectangular center strip and two lateral strips printed on a dielectric substrate and excited using a 50 Omega microstrip transmission line. The antenna generates two separate resonant modes to cover 2.4/5.2/5.8 GHz WLAN bands. Lower resonant mode of the antenna has an impedance bandwidth (2:1 VSWR) of 330 MHz (2190-2520 MHz), which easily covers the required bandwidth of the 2.4 GHz WLAN, and the upper resonant mode has a bandwidth of 1.23 GHz (4849-6070 MHz), covering 5.2/5.8 GHz WLAN bands. The proposed antenna occupy an area of 217 mm² when printed on FR4 substrate (epsiv_r=4.7). A rigorous experimental study has been conducted to confirm the characteristics of the antenna. Design equations for the proposed antenna are also developed     

基于高阻抗表面PBG结构微带天线的设计与分析

以高介电常数介质为基底,利用辐射贴片开槽和微带馈电技术,设计了一款尺寸仅为16mm×12.45mm的小型微带天线。通过在此天线微带贴片周围加载高阻抗表面型光子晶体,有效抑制了表面波,改善了以高介电常数介质为基底的贴片天线的性能,实现了一款多频小型化PBG天线。HFSS仿真结果表明,加载高阻抗表面结构后的微带天线出现了三个谐振频点,分别为2.74、2.86和3.80GHz,其对应的增益分别达到6.02、8.38和5.69dB。所设计的光子晶体天线物理尺寸较小,方向性良好且具有多频特性,因此可为实际通信天线的应用提供参考。     

螺旋带色散特性和耦合阻抗的精确计算

应用一种改进的计算螺旋带色散和耦合阻抗的方法,对面电流密度进行Chebyshev多项式展开后,去除了螺旋带上的面电流密度假设。在介质的高阶径向分层时为了避免高阶矩阵的求逆运算,采用转移矩阵和连接矩阵处理边界的场匹配。编写可径向任意分层的普适性程序,计算了螺旋线行波管的一些典型结构。研究表明:该理论的计算结果与实验结果有很好的一致;谐波次数以及面电流Chebyshev展开的项数完全可以依据结果的收敛性进行选取;分层的数目主要与结构的径向规则程度有关,径向越不规则,所要求的分层数目越多。     

Coplanar Waveguide: A Surface Strip Transmission Line Suitable for Nonreciprocal Gyromagnetic Device Applications

A coplanar waveguide consists of a strip of thin metallic film on the surface of a dielectric slab with two ground electrodes running adjacent and parallel to the strip. This novel transmission line readily lends itself to nonreciprocal magnetic device applications because of the built-in circularly polarized magnetic vector at the air-dielectric boundary between the conductors. Practical applications of the coplanar waveguide have been experimentally demonstrated by measurements on resonant isolators and differential phase shifters fabricated on low-loss dielectric substrates with high dielectric constants. Calculations have been made for the characteristic impedance, phase velocity, and ripper bound of attenuation of a transmission line whose electrodes are all on one side of a dielectric substrate. These calculations are in good agreement with preliminary experimental results. The coplanar configuration of the transmission system not only permits easy shunt connection of external elements in hybrid integrated circuits, but also adapts well to the fabrication of monolithic integrated systems. Low-loss dielectric substrates with high dielectric constants may be employed to reduce the longitudinal dimension of the integrated circuits because the characteristic impedance of the coplanar waveguide is relatively independent of the substrate thickness; this may be of vital importance for Iow-frequency integrated microwave systems.     

高阻表面交指形电容设计公式的改进

本文采用保角变换法和电容拼接技术对交指形电容进行精确的计算,对交指形高阻表面光子晶体设计公式进行了改进.该计算模型适用于宽范围的介电常数和介质层厚度,各指长度和缝隙宽度可以不同,并且很容易扩展到多层介质以及有覆盖层的情况.设计了三个光子晶体例子,对其表面波特性进行了模拟和测试,得出交指电容值,证明本文给出的计算公式更准确.     

Slotline impedance

A theoretical model is presented to compute the characteristic impedance and wavelength in a slotline printed on or embedded in a dielectric substrate. In this treatment the effects of the fringing field caused by the finite width of the conducting strips are taken into account. The main task is to calculate the capacitance per unit length of the slotline. First, the Green's function for the potential of a pair of filament sources in a dielectric substrate is solved; this is used as a building block to construct the overall solution of the boundary value problem. Then, the surface charge density on the conducting strips is found by using a moment method and imposing the source condition (equal potential) on the conductors. From the surface charge density, the characteristic impedance of the slotline is computed for various input parameters. The formulation is applicable to a single-sided, sandwiched, or double-sided slotline printed on or embedded in a dielectric substate     

Exact circuit analysis of spherical waves

A circuit representation for the impedance of spherical waves radiating from a spherical boundary was derived using a partial fraction expansion by Chu in order to establish gain bandwidth limitations for antennas. These circuits are derived directly from the recurrence relations for spherical Bessel functions. They provide an exact analog of the field solution both inside and outside of a spherical surface for any values of permittivity (epsilon) and permeability (mu). Since the circuits have the form of high-pass filters, they provide significant physical insight into scattering and radiation problems, suggest suitable asymptotic or approximate forms and allow circuit concepts and theorems to be brought to bear in order to solve specific configurations or to set general performance bounds. As an example of their application, compact computer programs for the radar cross section of conducting and dielectric spheres, the minimumQ's for antennas, theQ's and resonant frequencies of dielectric spheres and the induced current at the specular and shadow points of a conducting sphere are given. Other illustrative results are the short pulse responses of a solid dielectric and a dielectric-coated sphere computed using the circuit surge impedance and multiple reflection terms; and the response of a hypothetical scatterer in which the TE and TM modes are coupled.     

Resonance in spherical-circular microstrip structures

The resonance problem of a circular microstrip disk mounted on a spherical surface is studied theoretically. The radiator is replaced by a surface current distribution. The effects of the dielectric substrate as well as the curvature effect are taken into account by the Green's function formulation in the spectral domain. A vector Legendre series is defined. Cavity model current distribution is used as the current basis. Galerkin's procedure is used to solve for the complex resonant frequencies. Numerical results show that the effect of the curved surface on the resonant frequency and quality factor of the microstrip patch may be significant. In general, when the radius of the sphere is decreased, the effective radius of the patch will be reduced and the radiation loss is increased     

Aperture coupled dielectric resonator antenna with a thick groundplane

The aperture-coupled hemispherical dielectric resonator antenna with a thick ground plane is investigated theoretically and experimentally. The effects of the ground plane thickness on the input impedance, resonant frequency, and front-to-back radiation ratio are studied     

The resonant cylindrical dielectric cavity antenna

An experimental investigation of the radiation and circuit properties of a resonant cylindrical dielectric cavity antenna has been undertaken. The radiation patterns and input impedance have been measured for structures of various geometrical aspect ratios, dielectric constants, and sizes of coaxial feed probes. A simple theory utilizing the magnetic wall boundary condition is shown to correlate well with measured results for radiation patterns and resonant frequencies.