Scattered and internal intensity of a sphere illuminated with aGaussian beam

A method of calculating the internal and scattered electric fields of a spherical dielectric object illuminated with a Gaussian beam is presented. The vector nature of the beam is considered. The fields satisfy Maxwell's equations, and the beam can be located arbitrarily with respect to the object. A polarized Gaussian beam is first represented as an angular spectrum of plane waves. These waves are then expanded in vector spherical harmonics. Although the details of the expansion are presented for a lowest-order Gaussian beam, the method can be applied to any wave which can be expressed as a sum of homogeneous plane waves. The interaction of an arbitrarily located Gaussian beam with a spherical object is analyzed using the T-matrix method. Calculated results for beams having waists much smaller than the radius of the sphere help in visualizing how a narrow beam reflects and refracts at the spherical dielectric interfaces. The combination of the plane-wave spectrum technique and the T-matrix method can be applied to the problem of an arbitrary beam interacting with an axisymmetric, nonspherical, homogeneous or layered object     

Green's function for arbitrarily shaped dielectric bodies of revolution

In this paper, a solution is developed to calculate the electric field at one point in space due to an electric dipole exciting an arbitrarily shaped dielectric body of revolution (BOR). Specifically, the electric field is determined from the solution of coupled surface integral equations (SIE) for the induced surface electric and magnetic currents on the dielectric body excited by an elementary electric current dipole source. Both the interior and exterior fields to the dielectric BOR may be accurately evaluated via this approach. For a highly lossy dielectric body, the numerical Green's function is also obtainable from an approximate integral equation (AIE) based on a surface boundary condition. If this equation is solved by the method of moments, significant numerical efficiency over SIE is realized. Numerical results obtained by both SIE and AIE approaches agree with the exact solution for the special case of a dielectric sphere. With this numerical Green's function, the complicated radiation and scattering problems in the presence of an arbitrarily shaped dielectric BOR are readily solvable by the method of moments.     

Theory of aperture-coupled hemispherical dielectric resonator antennas with radiating elements

A new approach based on hybrid volume-surface integral equation (VSIE) formulation in combination with spherical dyadic Green's function (DGF) is presented in this paper to analyze aperture-coupled multilayer hemispherical dielectric resonator antennas (DRA) with conformal conducting patches. Hybrid VSIE is used for the planar part of the structure and is solved with the aid of spatial-domain method of moments (MoM) in order to compute magnetic surface current in a slot cut in a finite planar perfect electric conductor (PEC) sheet. Multilayer spherical electromagnetic DGFs are used to compute loading effects of hemispherical dielectric resonators and conformal patches on antenna characteristics. The effects of variation in some parameters of the structure on the return loss of the antenna are studied. Accuracy of the presented method is validated by comparing the results obtained from the proposed method with those of CAD simulations.     

Electromagnetic scattering by arbitrary shaped three-dimensional homogeneous lossy dielectric objects

The recent development and extension of the method of moments technique for analyzing electromagnetic scattering by arbitrary shaped three-dimensional homogeneous lossy dielectric objects is presented based on the combined field integral equations. The surfaces of the homogeneous three-dimensional arbitrary geometrical shapes are modeled using surface triangular patches, similar to the case of arbitrary shaped conducting objects. Further, the development and extensions required to treat efficiently three-dimensional lossy dielectric objects are reported. Numerical results and their comparisons are also presented for two canonical dielectric scatterers-a sphere and a finite circular cylinder.     

Effect of substrate on the efficiency of an arbitrarily shaped microstrip patch antenna

A general approach is presented for the determination of power radiated via the space wave and surface wave from the aperture of an arbitrarily shaped microstrip antenna. The magnetic current model is used for this, and the analysis is carried out in the Fourier domain to determine the effect of the substrate. It has been shown that, in the Fourier domain, the longitudinal components of electric and magnetic displacement vectors follow the transmission line equation and can be solved by inspection. An expression for total radiated power has been derived. The singularities of the integral for power radiation indicate the presence of surface wave modes, and the associated power has been obtained using a singularity extraction technique. The effect of the substrate on space wave power has also been determined. This theory has been applied to a rectangular patch antenna. The results are in conformity with those reported in the literature. It has been found that for the frequency range (h/lambda, < 0.02), the effect of dielectric substrate can be neglected.     

Corrugated spherical antenna

The radiation characteristics of a corrugated metallic sphere with an azimuthal slot are studied. For the purpose of analysis, a dielectric coating equivalent to the corrugation on the surface is assumed. Expressions for the equivalent relative permittivity, input admittance, gain and radiated far field, based on the boundary-value approach, are presented. For a spherical antenna of k0a = 4.9087 with corrugation corresponding to an equivalent dielectric coating of relative permittivity 8.36, it is shown that the increase in gain over the uncorrugated antenna is 6.15 dB. The above antenna was fabricated and the experimental pattern obtained is compared with the theoretical result.     

Radiation from a circular loop in the presence of sphericallysymmetric conducting or dielectric objects

The problem of electromagnetic radiation from a circular loop antenna of radius a, carrying a current I is considered. The loop may be radiating in the presence of one or more of the following objects: a centrally located dielectric or perfectly conducting sphere of radius ba and outer radius d, a perfectly conducting spherically symmetric cap at radius b, and another such cap at radius d. Typically geometric structures considered are shown. It is demonstrated how the presence of the sphere, shell, and caps can change and direct the radiation pattern of the loop     

金属介质混合目标电磁特性的快速分析

将自适应积分算法与基于体面混合积分方程的矩量法相结合快速分析任意结构金属/介质混合目标的电磁散射和辐射特性.通过将传统矩量法的阻抗矩阵分为两部分且采用不同的方法进行处理计算,提高了矩量法的计算速度并大幅度缩减了需要的计算机内存占用量.最后,分别用传统的矩量法与结合自适应积分快速算法的矩量法计算了三个典型例子,通过比较充分说明了文中方法的有效性.     

Analysis of arbitrarily shaped dielectric radomes using adaptive integral method based on volume integral equation

The adaptive integral method (AIM) is employed to solve the volume integral equation (VIE) for analyzing the radiation of the antenna with an arbitrarily shaped radome. Small dipoles are used as exciting sources. Modeling the radomes by tetrahedron cells, the induced volume current is determined by the AIM based on VIE. The application of AIM significantly reduces CPU time and computer memory requirement. Hence, the method presented in the paper can be applied to simulate electrically large sized radomes. Finally, the radiation patterns of small dipole arrays in the presence of spherical and conical radomes are calculated.     

任意形状线、面、体组成导体目标的电磁建模

本文用积分方程和矩量法分析具有任意线、面、体组成的理想导体目标的电磁散射和辐射特性.其中统一采用RWG基函数对线、面、体导体上的电流进行展开;对于任意的线-面,面-面连接情况,根据电流连续性条件,给出了通用的设置基函数和未知量的方法;对于辐射问题,给出了设置激励源与计算输入阻抗的方法.最后通过分析导体盒上的单极天线和宽带贴片天线验证了本文方法的可行性和有效性.     

Triangular ray-tube analysis of dielectric lens antennas

A new method of analysis for the radiation characteristics of dielectric lens antennas with arbitrary inner and outer surfaces is presented. The analysis is based on representing the feed illumination by a contiguous set of ray tubes and including the effects of surface reflections and ray divergence. Radiation patterns and the antenna gain are then computed by evaluating the closed-form expressions developed for the Kirchhoff's integral of the aperture fields. The validity of the analysis method has been demonstrated by comparing the computations with measured results of two different spherical lenses and a shaped lens configurations. The analysis method presented takes into account some of the practical aspects associated with lens design such as surface zoning to reduce the mass and surface matching to minimize the reflection loss     

Shaped reflector antenna analysis using the Jacobi-Bessel series

The physical optics approximation is employed to derive the radiation integral for a doubly curved offset reflector antenna illuminated by an arbitrary source. A novel procedure is presented for expressing the radiation integral in terms of a summation of Fourier transforms of an "effective" aperture distribution which includes the effect of the curvature of the surface. The Jacobi-Bessel series is used to evaluate the Fourier transforms. The vector nature of the far-field pattern is studied by evaluating its three Cartesian components in a unified fashion. The rapid numerical evaluations of the expressions obtained are demonstrated via extensive test cases. In particular, the scattering characteristics of symmetric and offset parabolic, spherical, and shaped reflectors are studied in detail, and comparisons are made with other available data.     

Waveguide excited microstrip patch antenna-theory and experiment

An arbitrarily shaped microstrip patch antenna excited through an arbitrarily shaped aperture in the mouth of a rectangular waveguide is investigated theoretically and experimentally. The metallic patch resides on a dielectric substrate grounded by the waveguide flange and may be covered by a dielectric superstrate. The substrate (and superstrate, if present) consists of one or more planar, homogeneous layers, which may exhibit uniaxial anisotropy. The analysis is based on the space domain integral equation approach. More specifically, the Green's functions for the layered medium and the waveguide are used to formulate a coupled set of integral equations for the patch current and the aperture electric field. The layered medium Green's function is expressed in terms of Sommerfeld-type integrals and the waveguide Green's function in terms of Floquet series, which are both accelerated to reduce the computational effort. The coupled integral equations are solved by the method of moments using vector basis functions defined over triangular subdomains. The dominant mode reflection coefficient in the waveguide and the far-field radiation patterns are then found from the computed aperture field and patch current distributions. The radar cross section (RCS) of a plane-wave excited structure is obtained in a like manner. Sample numerical results are presented and are found to be in good agreement with measurements and with published data     

Space-time integral equation approach to dielectric targets

A time-domain integral equation technique is presented for computing the response of arbitrarily shaped three-dimensional nondispersive homogeneous dielectric solids. The method is an extension of the previously reported space-time integral equation (STIE) approach to scattering from conducting solids. It consists of the simultaneous solution of four integral equations by a procedure of marching in time. The incident pulse-width is of the order of a target dimension. The result is a "smoothed impulse response," or, after deconvolution, a frequency response valid from dc through the resonance region. While applicable to arbitrary shapes, the numerical solution was implemented for smooth solids with plane symmetry. Results for a sphere and a sphere-capped cylinder are given and verified, respectively, by comparison with the Mie series solution and with measurements.     

Characteristics of space and surface waves in a multilayeredstructure [microstrip antennas]

Characteristics of space- and surface-wave fields produced by an electromagnetic source in a multilayered structure are explored. Using the integral transformation technique it is shown that the space and surface-wave modes are orthogonal along the longitudinal direction with respect to an appropriate weighting function. It is demonstrated that these properties, together with reciprocity, can be utilized to determine the amplitudes of various surface-wave modes produced by an arbitrarily shaped source. Numerical results for the space- and surface-wave power for a circular patch antenna are presented. The study may find application for millimeter-wave printed antennas where the surface waves will play an important role in determining the radiation and impedance characteristics     

Radar cross section of arbitrarily shaped bodies of revolution

The radar cross section (RCS) of an arbitrarily shaped, homogeneous dielectric body of revolution (BOR) is evaluated by the surface integral equation (SIE) formulation and the method of moments. Method accuracy is verified by the good agreement with the exact solutions for the RCS of a dielectric sphere. To demonstrate the advantages of this method, the RCS for a complex BOR model of human torso is computed with a nonaxially incident plane wave. Seven Fourier modes are considered in the computation. The SIE and approximate integral equation (AIE) formulations are next given for the RCS evaluation of a composite dielectric and conducting BOR. For the cases considered, both formulations give the same surface currents and RCS results. However, significant savings in computer storage and CPU time are realized for the AIE approach, since only one current (electric or magnetic) need be determined for RCS evaluation     

任意形状天线罩的快速分析

将自适应积分算法与体积分方程相结合分析任意形状天线罩对天线辐射特性的影响。将任意形状的天线罩剖分成四面体，基于体积分方程的自适应积分快速算法求出天线罩上的感应电流，即可求出天线-天线罩系统的总场。自适应积分快速算法的应用提高了矩量法的计算速度，并大大缩减了需要的存储量，从而使该方法可用于分析电尺寸较大的天线罩.最后,分别计算了球形、锥形天线罩存在时理想电振子阵列的辐射方向图。     

Electromagnetic Radiation by Antennas of Arbitrary Shape in a Layered Spherical Media

A unified method of moments model is developed for the analysis of arbitrarily shaped antennas that are radiating next to a multilayered dielectric sphere. The curvilinear Rao-Wilton-Glisson triangular basis functions and dyadic Green's functions have been used in the model. Antennas of various geometries including spherical, circular and rectangular microstrip antennas as well as hemispherical dielectric resonators have been modeled. Input impedance and radiation pattern results are presented and shown to be in good agreement with published data.      

Analysis of Antenna Around NURBS Surface With Hybrid MoM-PO Technique

The hybrid method of moments and physical-optics (MoM-PO) approach is used to calculate the radiation pattern of antenna around arbitrarily shaped structure. The structure is modeled with Non-uniform rational B-spline (NURBS) surfaces. The hybrid MoM-PO approach is implemented by modifying the impedance matrix of the MoM region with PO. Formula for the scattered PO field is deduced for cases of antenna located around NURBS surface. The stationary phase method (SPM) is applied for the integral of the induced current in the PO region. Results obtained from this method and from MoM-PO approach based on triangle facet model agree well while the former is more efficient in execution time     

Numerical analysis of arbitrarily shaped probe-excited single-armprinted wire antennas

A general integral equation technique is described for analysis of an arbitrarily shaped single-arm printed wire antenna excited through a vertical probe. A unified current integral equation is formulated on the basis of dyadic Green's functions and the reciprocity theorem. The current distribution is obtained by using a parametric moment method in which parameter segments are adopted for the printed wire instead of the commonly employed wire length segments. The radiation field solution involving both the printed antenna and vertical probe is also presented. The validity of the formulation is verified by comparing the numerically obtained input impedance and radiation patterns for a linear antenna and a meander antenna with measured data. A circular open loop and an Archimedian spiral are investigated to illustrate the applicability of the present technique