导体介质组合体电磁分析的建模与计算

为提高导体介质复合目标电磁散射分析的效率,采用一类新的表面混合场积分方程进行求解,该方程通过伽略金方法建立的阻抗矩阵具有良好的条件数.分析了多区域连接边上的电磁流分布和基函数的定义,然后根据边界条件推导了广义EFIE-CFIE-JMCFIE方程形式,最后比较了不同积分方程建立阻抗矩阵的收敛性.数值算例表明该方法能明显提高计算效率,实现导体介质复合目标电磁散射分析快速、准确的求解.     

介质目标电磁散射特性的多层特征基函数法分析

特征基函数法是近几年提出的一种基于分块和高阶基函数概念求解电磁散射问题的快速算法.为了更有效地分析电大尺寸多目标的电磁散射问题,将基于Foldy-Lax多径散射方程的特征基函数法扩展为多层特征基函数法,通过对子域进行多层划分来控制生成矩阵维数的大小和计算精度.应用多层特征基函数法计算了介质目标的远区散射场,数值结果与传统特征基函数法的计算结果吻合良好,且计算效率明显提高.     

一种快速分析多导体宽带电磁散射的方法

应用特征基函数法和渐近波形估计技术分析了二维多导体目标的电磁散射特性。特征基函数法对问题中的每个子域构造了一种包含散射问题不同域间的耦合效应的高级基函数,降低了生成的全局矩阵维度,从而可以对矩阵进行快速求解得到目标的表面电流,并结合渐近波形估计技术计算目标的宽带雷达散射截面。数值计算表明:计算结果与矩量法逐点计算结果相吻合,计算效率大大提高。     

金属-各向异性介质体组合目标频域体表积分方程矩量法

利用体表积分方程矩量法求解了具有任意的介电常数张量和磁导率张量的各向异性介质与金属的组合目标的电磁散射问题.给出了基于RWG面基函数和SWG体基函数的体表积分方程阻抗矩阵元素表达式并详细推导了阻抗矩阵元素所涉及的各种积分运算的计算方法;通过数值计算实例与解析解或其它数值方法的详细对比分析,证明了计算公式的正确性.     

三维导体介质复合结构电磁辐射与散射的MLFMA分析

利用多层快速多极子方法(MLFMA)分析三维导体介质复合结构的电磁辐射与散射特性.根据等效原理,介质表面构造Poggio-Miller-Chang-Harrington-Wu(PMCHW)方程,导体表面建立电场积分方程(EFIE).分析了含介质目标MLFMA算法中远区组矩阵矢量相乘运算以及有耗媒质空间中格林函数的平面波展开.利用该方法研究了涂敷目标电磁散射特性以及天线罩对直线阵天线辐射特性的影响.MLFMA的应用降低了计算量和存储量,实现了对电大尺寸目标快速、准确的求解.     

均匀有耗涂层目标的电磁散射分析

采用表面电场和磁场积分方程及矩量法计算了涂层导体/介质目标的双站雷达散射截面,介质是均匀各向同性有耗的.首先利用等效原理建立介质/导体表面的电磁场积分方程,然后采用伽略金法将积分方程组转化为矩阵,求解出涂层表面的等效电磁流后,就可计算目标的散射场.通过对均匀有耗涂层导体球利用解析法[1]和矩量法两种方法进行计算,验证了本文方法的准确性.     

手征材料涂覆导体目标电磁散射特性的PO分析

从Maxwell方程出发 ,推导出平面波照射下手征介质涂覆导体目标表面等效电磁流的一般表达式 ,并基于切平面近似 ,给出了计算手征介质涂覆导体目标电磁散射的物理光学 (PO)解。在此基础上 ,计算了T形结构及锥柱结构的散射特性 ,分析了手征材料参数对电磁散射的影响 ,得到了一些有益的结果。为电大尺寸手征介质涂覆导体目标电磁散射特性的快速估计提供了一种有效的手段     

二维多导体柱电磁散射特性的特征基函数法分析

特征基函数法是近两年提出来的一种求解电磁散射问题的有效方法,该方法使用的特征基函数不受传统矩量法离散尺寸的限制,因而可以大大减小要求解的矩阵方程。应用特征基函数法分析了二维多导体柱的电磁散射特性,计算了多个无限长导电椭圆柱和方柱的雷达散射截面,结果表明特征基函数法的计算结果与传统矩量法的计算结果吻合良好,而计算量却大为减少。     

介质体电磁散射分析中的等效偶极矩法

在介质体电磁散射分析中,提出了一种基于等效偶极矩法的快速矩阵生成技术。该方法以矩量法和RWG基函数为基础,将源点处的电(磁)流等效为电(磁)偶极子,因而阻抗矩阵元素可以认为是源点电(磁)偶极子所产生的近区场与场点电流基函数之间的相互作用。这样等效偶极矩法避免了格林函数二重积分,使得阻抗矩阵元素的生成速度明显提高。数值结果表明该方法有较高的计算效率和精度。     

T矩阵递推算法用于二维混合目标RCS计算

利用递推算法计算任意形状二维导体加介质体目标的电磁散射。建立导体部分单独存在时的T矩阵，对于内谐振频率点上生成的病态矩阵用奇异值分解方法解决，用广义递推算法求出有耗介质单体T矩阵。然后采用二体散射的方法求得总散射场。计算结果表明了该方法的正确性。     

Electromagnetic scattering from composite objects using a mixtureof exact and impedance-boundary conditions

Different surface integral equations for characterizing the electromagnetic scattering from a surface impedance object partially coated with dielectric materials are presented. The impedance boundary condition (IBC) is applied on the impedance surface and the exact boundary condition is applied on the dielectric surface. The resulting integral equations are solved for bodies of revolution using the method of moments. The numerical results are compared with the exact solution for a sphere. Other geometries are considered, and their results are verified by comparing results of the numerical solutions which were obtained using different formulations. The internal resonance problem is examined. It is found that the combined field integral equation (CFIE) can be used at any frequency and with any surface impedance     

Electromagnetic radiation of antennas in the presence of anarbitrarily shaped dielectric object: Green dyadics and theirapplications

Although numerical solutions to the electromagnetic scattering by an arbitrarily shaped object have been obtained using Waterman's (1971) T-matrix method (TMM), the general electromagnetic radiation due to an antenna of a three-dimensional (3-D) current distribution in the presence of an arbitrarily shaped object has not been well considered. In this paper, the technique of surface integral equations has been employed; and as a result, a terse and analytical representation of the dyadic Green's functions (DGFs) in the presence of an arbitrarily shaped dielectric object is obtained for the antenna radiation. In a form similar to that associated with the electromagnetic radiation in the presence of a dielectric sphere, the DGFs inside and outside of the object of arbitrary shape are expanded in terms of spherical vector wave functions. However, their coefficients are no longer decoupled due to the arbitrary surface of a 3-D object. The coupled coefficients are then determined using the surface integral equation approach, in a fashion similar to that in the T-matrix method. To confirm the applicability and correctness of the approach in this paper a dielectric sphere, as a special case, is utilized as an illustration. It is found that exactly the same expressions as in the rigorous analysis for the inner and outer spherical regions of the object are obtained using the different approaches. As applications of the approach in this paper, radiation problems of an electric dipole in the presence of superspheroids and rotational parabolic bodies are solved     

Extended integral equation formulation for scattering problems froma cylindrical scatterer

An extended integral equation is developed for electromagnetic scattering from a perfectly conducting cylinder and a dielectric cylinder. The conventional surface integral equations cannot yield unique solutions when the wavenumber of the electromagnetic wave is equal to an eigenwavenumber of the system. Several methods to overcome this difficulty have been presented, but each method includes some drawbacks. A numerical method is proposed in which the boundary element method is applied to the extended integral equations with the observation points lying on a closed surface inside the scatterer. It is shown that the extended integral equations have unique solutions for any given wavenumber. As examples, plane wave scattering from a perfectly conducting elliptic cylinder, a dielectric elliptic cylinder, and a dielectric rectangular cylinder is numerically analyzed     

Single integral equation for electromagnetic scattering bythree-dimensional homogeneous dielectric objects

A single integral equation formulation for electromagnetic scattering by three-dimensional (3-D) homogeneous dielectric objects is developed. In this formulation, a single effective electric current on the surface S of a dielectric object is used to generate the scattered fields in the interior region. The equivalent electric and magnetic currents for the exterior region are obtained by enforcing the continuity of the tangential fields across S. A single integral equation for the effective electric current is obtained by enforcing the vanishing of the total field due to the exterior equivalent currents inside S. The single integral equation is solved by the method of moments. Numerical results for a dielectric sphere obtained with this method are in good agreement with the exact results. Furthermore, the convergence speed of the iterative solution of the matrix equation in this formulation is significantly greater than that of the coupled integral equations formulation     

Improving Conditioning of Electromagnetic Surface Integral Equations Using Normalized Field Quantities

When the surface integral equation method is applied to study electromagnetic scattering by dielectric or composite metallic and dielectric objects, the unknowns, i.e., the electric and magnetic surface current densities, and the elements of the system matrix, are often of the very different scales. As a consequence, the system matrix may have a high (singular value) condition number. An efficient method is presented to balance the unknowns and the integral equations, and the elements of the system matrix, too. The method is based on the use of normalized field quantities and unknowns, and carefully chosen scaling factors. In the case of dielectric and composite objects the condition numbers of the SIE matrices can be reduced with several orders of magnitudes by the developed method. In the case of high contrast objects, or if the frequency is very low, the developed method leads also to a clear improvement on the convergence of iterative solutions     

Scattering from dielectric structures above impedance surfaces andresistive sheets

Interest in understanding of electromagnetic interaction with rough surfaces has prompted the study of scattering from typical dielectric humps over impedance surfaces. It is shown that the Green's function of the problem for a resistive sheet resembles that of the impedance surface. Hence both problems are considered here. A numerical solution for the scattered field of a two-dimensional dielectric object, possibly inhomogeneous, with arbitrary cross section above the impedance surface or resistive sheet is sought. First the Green's function of the problem is derived based on the exact image theory. This form of the Green's function is amenable to numerical computation. Then the induced polarization currents are calculated by casting the integral equations into a matrix equation via the method of moments. Numerical problems in calculation of the Green's function when both source and observation points are close to the surface are discussed. Comparison of numerical results with a perturbation solution shows excellent agreement between the two methods     

Electromagnetic scattering from objects composed of multiplehomogeneous regions using a region-by-region solution

The paper presents an efficient procedure to calculate the electromagnetic field scattered by an inhomogeneous object consisting of N+1 linear isotropic homogeneous regions. The procedure is based on surface integral equation (SIE) formulations and the method of moments. The method of moments (MM) is used to reduce the integral equations for each homogeneous dielectric region into individual matrices. These matrices are each solved for the equivalent electric current in terms of the equivalent magnetic current. A simple algebraic procedure is used to combine these solutions and to solve for the magnetic current on the outer dielectric surfaces of the scatterer. With the magnetic current determined, the electric current on the outer surface of the scatterer is calculated. Because the matrix corresponding to each dielectric region is solved separately, the authors call this procedure the region-by-region method. The procedure is simple and efficient. It requires less computer storage and less execution time than the conventional MM approach, in which all the unknown currents are solved for simultaneously. To illustrate the use of the procedure, the bistatic and monostatic radar cross sections (RCS) of several objects are computed. The computed results are verified by comparison with results obtained numerically using the conventional numerical procedure as well as via the series solution for circular cylindrical structures. The possibility of nonunique solutions has also been investigated     

Analyse de structures tridimensionnelles inhomogenes quelconques

This paper illustrates the capability of SR3D software to rigorously analyze 3D radiating structures including wires (thin or thick), dielectric parts and finite ground planes. The analysis method is within the class of bound ary element method (bem) and use integral equation formulation (combined field integral equation cfie) to solve electromagnetic scattering problems. It includes a variational approach based on Rumsey reaction concept. The problem is numerically solved with a surface finite element method : surfaces of 3D conducting object and interfaces between dielectric domains are meshed using surface triangular patches. We discuss on the numerical options chosen, the basis functions used, discretization density, and treatment of wires. The last sections emphasize the accuracy of the method on examples for which computed and measured reflection coefficient and radiation patterns are compared.     

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.     

高斯粗糙面与临空目标复合电磁散身寸的KH-MOM解

提出了一种求解一维粗糙面与二维无限长临空目标复合电磁散射特性的新型混合算法。混合算法只需在粗糙面上进行一次积分运算,即可用基尔霍夫-亥姆霍兹方程(KH)描述电磁波经粗糙面后的散射情况,再用矩量法(MoM)分析目标的散射问题,通过KH与MoM的混合来体现粗糙面与目标之间的耦合作用。经与不同方法的对比,验证了混合方法的正确性,体现了混合方法较数值法在求解效率上的巨大优势。计算了粗糙面与临空目标的统计复合散射特性,分析了粗糙面的起伏参数、临空目标的形状以及粗糙面介质的电参数对复合散射特性的影响。