探针馈电印刷线天线的矩量法分析——（Ⅰ）单臂天线

利用同轴内导体延和为探针对印刷天线进行直接馈电是一种易于实现的馈电方式。本文介绍了一种分析单臂探针馈电印刷线天线的数值方法,该方法是基于并矢格林函数和互易定量求解电流积分方程的矩量法,适合于分析任意形状印刷线天线,首先给出描述电流分布的积分方程及其矩量法求解公式,在解得电流分布基础上,应用驻相法计算远区辐射场,通过计算与实验比较,验证了分析方法和计算程序的正确性,最后对一圆极化开口印刷圆环天线进行分析计算,表明了方法的实用价值。     

探针馈电印刷线天线的矩量法分析——（Ⅱ）多臂天线

通过应用模式分解法,本文将单臂探针馈电印刷线天线的分析方法推广到具有旋转对称性的任意多臂探针馈电印刷线天线的分析计算。首先给出探针馈电N臂印刷线天线的电流积分方程、矩量方程及远区辐射场计算公式;通过一个中心馈电螺旋天线的分析计算验证方法和计算程序的正确性;设计出具有良好圆极化特性的开口双圆环印刷线天线;最后分析了一探针馈电四臂印刷螺旋天线的辐射特性。     

微带印刷天线辐射与散射的全波分析方法

本文给出了一种分析微带印刷天线辐射与散射的数值方法。此方法将印刷天线按三角网格剖分，在导体表面建立积分方程，用全波离散镜像理论给出微带结构的空域格林函数的闭合表达式，未知电流用三角网格上的矢量电流基函数展开并用矩量法求解。与以往的矩形网格上基函数展开相比，此方法能更有效地逼近任意形状的微带结构，最后给出了几个数值结果     

The moment method solution for printed wire antennas of arbitraryconfiguration

A printed wire antenna of arbitrary configuration is analyzed. The electric field tangential to the wire is derived using the current expanded by piecewise sinusoidal functions. These functions are also used to form the impedance matrix elements. Use of the stationary phase method leads to a simple expression for the radiation field. Numerical analyses based on the present formulation yield radiation characteristics of a zigzag dipole antenna, a loop antenna, and a round spiral antenna     

Folded loop antenna for mobile hand-held units

The vertical folded loop antenna, modeled as wire and printed radiating element mounted on a conducting box, simulating a cellular telephone with and without dielectric coating, is analyzed. The finite-difference time-domain (FDTD) method is used to calculate radiation patterns and input impedance. The results are compared with measurements and with NEC data. Very good agreement is obtained in all cases. Parasitic loading is used to enhance the bandwidth of the printed element. The antenna meets the design requirements for existing and future mobile communication systems     

Antenne unipolaire cylindrique alimentée par un cable coaxial. problème des singularités et applications en basse fréquence

In the integral equation approach to the antenna radiation problem, the current on the antenna and an accurate modelization of the generator are needed. Moreover the kernel of the integral equations is singular. This paper, presents a rigorous solution of these equations in the case of a wire antenna mounted on a perfectly conducting plane, and feeded by a coaxial cable. The current on the antenna and the field inside the cable are accurately determined. At low frequencies, the techniques used to avoid the singularity in the kernel allows a fast computation of the unknown current and field.     

Analysis of dielectric-resonator antennas with emphasis onhemispherical structures

An overview is given for the development of dielectric-resonator antennas. A detailed analysis and study of the hemispherical structure, excited by a coaxial probe or a slot aperture, is then given, using the dyadic Green's functions pertaining to an electric-current source or a magnetic-current source, located in a dielectric sphere. The integral equation for a hemispherical dielectric-resonator antenna (DRA), excited by either a coaxial probe or a slot aperture, is obtained. The integral equation is solved using the method of moments. The antenna characteristics, such as input impedance, radiation patterns, directivity, and efficiency, are computed numerically, around the resonant frequency of the TE₁₁₁ mode (the HEM₁₁ mode for cylindrical coordinates). The computed input impedance is compared with numerical and experimental data available in the literature     

Current distribution and input impedance of printed dipoles

Printed dipole antennas find increasing use in microwave as well as far infrared frequencies. The current distribution, input impedance, and radiation pattern are computed for wire antennas printed on a dielectric substrate. The current distribution is obtained by solving Pocklington's equation by moment methods. The Green's function pertinent to the problem involves improper Sommerfeld-type integrals. These integrals are computed by a real-axis integration technique which involves analytical and numerical steps. The effect of surface modes is carefully taken into account.     

An integral equation and its application to spiral antennas onsemi-infinite dielectric materials

This paper presents an integral equation that can handle wire antennas on a semi-infinite dielectric material. The integral equation is reduced to a set of linear equations by the method of moments. For efficiency, the impedance matrix element Z_m,n is divided into two parts on the basis of weighted Green's function extractions. The far-zone radiation field, which is formulated using the stationary phase method, is also described. After the validity of the presented numerical techniques is checked using a bow-tie antenna, a spiral antenna is analyzed. The current distribution, radiation pattern, axial ratio, power gain, and input impedance are discussed. It is found that the radiation field inside a dielectric material is circularly polarized. As the relative permittivity of the dielectric material increases, the angle coverage over which the axial ratio is less than 3 dB becomes narrower     

Very compact double C-patch antenna

A miniaturised C-patch antenna excited by means of a coaxial probe is described. The antenna consists of two stacked C-shaped elements connected together with a vertical conducting plane. The antenna is designed on an air substrate and offers attractive dimensions, being five times lower than those of a conventional half wavelength microstrip patch antenna operating at the same frequency. A 10 dB bandwidth of 3% is obtained. The voltage standing wave ratio, radiation patterns, and electric surface current density are presented     

Complex resonance and radiation of hemisphericaldielectric-resonator antenna with a concentric conductor

The probe-fed hemispherical dielectric-resonator antenna (DRA) with a concentric conductor is studied theoretically in this paper. Using the mode-matching method, the exact Green's functions for evaluation of the input impedance and radiation patterns are found, with the functions presented in computationally efficient forms. The moment method is used to determine the probe current and, hence, the input impedance as well as the radiation patterns. The results are verified by special cases available in the literature. In this paper, the effects of the conductor radius, dielectric constant, probe length, and probe displacement on the input impedance are investigated. The theory is very general and, by taking appropriate limits, can be used to study the solid DRA and the conductor-loaded wire antenna. To aid the DRA design engineer, the TE₁₁₁-mode characteristic equation of the DRA is also studied, from which the simple formulas for the resonant frequency and Q-factor are obtained     

Frequency characterization of a thin linear antenna using diakopticantenna theory

A frequency-dependent analytical expression for the input impedance of a thin wire antenna is obtained using diakoptic theory. The linear antenna is diakopted into electrically short segments, where each is treated as a component with two terminals (except for end pieces, which have only one terminal). An impedance matrix is found which characterizes coupling between all segments. By expanding the free-space Green's function in a power series in wavenumber k, each entry in the resultant impedance matrix is obtained as an explicit function of frequency. The input admittance is found as a ratio of two polynomials in wavenumber k. A more systematic approach for the solution of the input admittance is achieved by expanding both the unknown current vector and the Green's function in power series in k. Equating coefficients of like powers in k leads to a numerically efficient algorithm which is used to determine the input admittance as a function of frequency. Numerical results compare well with the input impedance obtained from a conventional integral equation solution     

Electromagnetic analysis of an antenna embedded in a compositeenvironment

This paper addresses the problem of an antenna embedded in a hole dug in the ground. The composite medium configuration consists of a half-space dielectric (representing the Earth-air interface) containing a cylindrical hole filled with a different dielectric medium. The wire antenna resides within this hole, on the axis. The solution strategy is based on decomposing the problem into simpler subproblems, which are treated sequentially. First we calculate a numerical dyadic Green's function for the composite medium by solving an integral equation formulated over a background consisting of the unperturbed dielectric half space (for which the Green's functions are known in a spectral integral form). This integral equation is solved via the fictitious currents method, which is a special case of the method of moments. We then solve the integral equation for the antenna currents using this numerical Green's function and determine the input impedance and radiation pattern     

Analysis of a Wire Antenna in the Presence of Sphere

An integro-differential equation is formulated for the problem of a thin-wire antenna in the presence of a sphere, and this equation is solved by the method of moments. The analysis is valid for an arbitrarily oriented and positioned wire relative to the sphere which may be either a perfect conductor or may be any simple homogeneous material. Input admittance of the wire antenna near a conducting sphere is determined from computed wire current and is corroborated by measured values of admittance. Also presented are calculated radiation patterns for the antenna/sphere structure.     

多层电厚微带天线的阻抗特性

本文提出了一种多层介质电厚微带天线的一种分析方法。从无界空间中的电并矢格林函数出发,导出了分层介质中任意一点具有任意取向的水平电偶极子场的表达式。以此为基础,利用Richmond反作用积分方程,建立了关于贴片上电流分布的积分方程。通过适当选取电流基函数,使本方法适用于电厚介质微带天线。应用Galerkin方法建立矩阵方程。借助于计算机求解该矩阵方程,可得到天线的各项特性。文中用实例进行了验证。     

A notch-wire composite antenna for polarization diversity reception

This paper presents a notch-wire composite antenna for polarization diversity reception in an indoor base-station system. A three-notched disk antenna and a wire antenna are proposed as component antennas for the horizontal and the vertical polarization, respectively. These component antennas are unified as a single composite diversity antenna by mounting the wire antenna on the notched disk. Antenna characteristics are calculated using the method of moments (MoM), with wire grid models and examined in terms of component arrangement, and terminal isolation. It is found that maximum isolation is obtained when the current path of the wire antenna is where the current exciting the H-pol element is cancelled. Consequently, both component antennas may work independently even in the composite form. The quasi-monopole pattern is also confirmed for each polarization     

The short-pulse response of a straight wire

A numerical method for solving a time-dependent thin-wire electric-field integral equation is briefly described. Results obtained for a straight wire antenna and scatterer excited by a time-varying Gaussian pulse and valid to a maximum wire length of approximately 10 wavelengths are presented.     

Loaded horizontal antenna over an imperfect ground

The Fresnel reflection coefficient technique is employed to establish anE-field integral equation for the antenna current. A resistive loading of the formLambda(x) = Lambda_{0}/(1 - |x|/L)is used to load the antenna. An optimization technique is discussed for determining the value of critical loadingLambda_{0}^{c}, which enforces a traveling wave current on the antenna. Results are given for the critical loading parameters, antenna currents, input impedances and radiation patterns versus different antenna dimensions and ground permittivities and conductivities. Some representative time-domain results for such loaded antennas are also included.     

Radiation of printed antennas with a coplanar waveguide feed

This paper presents an analysis of conductor-backed aperture antennas with multilayered substrate. These printed antennas are fed by a coplanar waveguide (CPW). The theoretical approach taken is to develop an integral equation over the aperture region and apply Galerkin's procedure in the spectral domain. The properties of printed antennas with a CPW feed are characterized. Numerical results include the scattering parameters, antenna pattern, and radiation efficiency. The reflection coefficient, input impedance, and far-field pattern are also compared with measurements and good agreement is observed     

A broad-band U-slot rectangular patch antenna on a microwavesubstrate

A broad-band U-slot rectangular patch antenna printed on a microwave substrate is investigated. The dielectric constant of the substrate is 2.33. The antenna is fed by a coaxial probe. The characteristics of the U-slot patch antenna are analyzed by the finite-difference time-domain (FDTD) method. Experimental results for the input impedance and radiation patterns are obtained and compared with numerical results. The maximum impedance bandwidth achieved is 27%, centered around 3.1 GHz, with good pattern characteristics