一维FSS电磁散射宽带特性的快速计算

基于渐近波形估计（AWE）技术和矩量法（MOM），快速分析了一维频率选择表面（FSS）的宽带电磁散射特性，首先采用MOM法将平面波照射下FSS的电场积分方程（EFIE）转化为关于感应电流的矩阵方程，并由该方程确定频率导数矩阵方程（MEFD）；再在所考虑的频带内的某一给定频率处求解MEFD，得到给定频率处的频率导数感应电流；最后根据Pade逼近理论由给定频率处的频率导数感应电流确定周期性结构在任意频率入射波照射下的感应电流，根据FSS上的感应电流及谱域Floquet谐波模计算FSS的电磁散射宽带特性，计算结果表明，AWE能有效逼近MOM逐点扫描计算的结果，同时在计算速度上可加快十几倍。     

基于相关全息原理的散射成像技术及其进展

由于随机散射效应,相干光束经过强散射介质后,出射光场变成光强呈无序分布的散斑场,因此无法直接从出射场获取入射光的信息。然而,在随机散射过程中,出射散斑场仍然携带着入射光场信息。从散斑场中获取原始信息以实现物体的重建是一个备受关注的研究课题。研究人员针对该问题提出了包括散斑相关、传输矩阵、波前调控及时间反演与相位共轭等技术。着重介绍了基于相关全息原理的散射成像技术,主要包括其原理、发展历史以及最新的研究进展,并对该技术的未来发展趋势进行了展望。     

Adaptive multiscale moment method (AMMM) for analysis of scatteringfrom three-dimensional perfectly conducting structures

The adaptive multiscale moment method (AMMM) is presented for the analysis of scattering from three-dimensional (3D) perfectly conducting bodies. This algorithm employs the conventional moment method (MM) using the subsectional triangular patch basis functions and a special matrix transformation, which is derived from solving the Fredholm equation of the first kind by the multiscale technique. This methodology is more suitable for problems where the matrix solution time is much greater than the matrix fill time. The widely used triangular patch vector basis functions developed by Rao et al., (1982), are used for expansion and testing functions in the conventional MM. The objective here is to compress the unknowns in existing MM codes, which solves for the currents crossing the edges of the triangular patch basis functions. By use of a matrix transformation, the currents, source terms, and impedance matrix can be arranged in the form of different scales. From one scale to another scale, the initial guess for the solution can be predicted according to the properties of the multiscale technique. AMMM can reduce automatically the size of the linear equations so as to improve the efficiency of the conventional MM. The basic difference between this methodology and the other wavelet-based techniques that have been presented so far is that we apply the compression not to the impedance matrix but to the solution itself directly in an iterative fashion even though it is an unknown. Two numerical results are presented, which demonstrate that the AMMM is a useful method for analysis of electromagnetic scattering from arbitrary shaped 3D perfectly conducting bodies     

用于处理六边对称结构电磁散射的GIM技术

利用散射体的几何对称特性，使各种矩阵方法（指通过离散化，最终导致应用矩阵求解的数值方法）求解散射场过程中所需要的存储单元和时间减少，是当前具有理论和实际意义的重要课题。为此，本文在广义镜像法原理（GIM）的基础上，给出了处理一种具有六边对称结构的电磁散射问题的新方法。本文的结果表明：在计算散射体形状为六边对称的散射场的过程中，能够使所需总的矩阵阶数降至1／4，所需总的运算时间降至约1／32。这一运算结果较之于原来的GIM方法处理同一问题，在不降低运算精度的情况下．可使运算时间和运算所需的存储量节约近一倍。     

周期性结构电磁感应电流宽带特性的快速计算

采用MOM法将周期结构的电场积分方程转化为关于感应电流的矩阵方程和频率导数矩阵方程，并根据Pade逼近理论由给定频率处的频率导数感应电流确定周期性结构在任一频率入射波照射下的感应电流，进而计算周期性结构的电磁感应电流宽带特性。计算结果表明，AWE在计算速度上比MOM可加快十几倍。     

A hybrid BEM/WTM approach for analysis of the EM scattering fromlarge open-ended cavities

An effective hybrid boundary-element method (BEM) and wavelet-transform method (WTM) is proposed to analyze electromagnetic scattering from three-dimensional (3-D) open-ended cavities with arbitrary shapes. This hybrid technique formulates the original cavity problems by a magnetic field integral equation. The BEM is employed to establish the mapping between the original complex integral surface and the unit square. The WTM is used to reduce the density of the moment matrix. Since a surface integral equation has to be solved, the WTM requires a two-dimensional (2-D) wavelet basis to implement the numerical computation. The previous fast iterative algorithm for 2-D wavelets has been extended for efficiently constructing various 2-D wavelet basis functions by a tensorial product from two one-dimensional (1-D) regular multiresolution analyses. Unlike the conventional method of moments, the proposed hybrid technique can always obtain sparse moment matrix equations, which can be efficiently solved by sparse solvers. As the level scales for numerical discretization of cavities increase, larger compression rates can be obtained, which makes it possible for the hybrid BEM/WTM technique to efficiently solve scattering from large open-ended cavities with complex terminations. Numerical results are presented to demonstrate the merits of the proposed method     

一种新的基于非反射对称非负特征值分解的Freeman分解

该文首次推导出了在非反射对称情况下非负特征值分解(NNED)的分析解法,即非反射对称NNED;并将其应用于Freeman分解,提出了一种基于非反射对称NNED的Freeman分解.在Freeman分解中,非反射对称NNED用于提取体散射功率,并用于调整体散射、二面角散射以及表面散射功率以确保余项协方差矩阵没有负特征值.相比于基于反射对称NNED的Freeman分解,所提的分解方法有效地利用了在反射对称条件下被假定为0的非对角线元素,能保证余项协方差矩阵没有负特征值,实测极化SAR数据实验表明,所提的分解方法能显著地加强城区的二面角散射功率并且减少城区的体散射功率.     

AWE在双负媒质宽频散射分析中的应用

该文旨在利用渐近波形估计(AWE)技术来研究双负媒质(DNG)的电磁散射特性。文章首先从双负媒质(DNG)的本构关系出发,推导出DNG的PMCHWT方程,从而解出单频率入射波下的电流和雷达散射截面(RCS);通过对阻抗矩阵元素的处理,实现了阻抗元素高阶导数的求解,成功的将AWE技术应用于DNG宽频电磁计算领域。计算实例表明:AWE计算的结果能很好地逼近精确解,同时大大提高了计算效率。     

基于Hemite外推的多柱体时频域电磁散射计算

首先根据散射体在高斯脉冲平面波激励下感应电流的能量几乎全部集中在时间轴和频率轴上的有限范围内,该文将时域响应展开为系数待定的连带Hermite级数的叠加,并根据连带Hermite函数的傅里叶变换的自反性,得到与时域响应形式类似的频域响应;然后利用时域方法和频域方法分别计算散射体上感应电流的早时响应和低频信息;最后经过时域和频域联合外推计算,由早时响应和低频信息确定时域和频域响应的待定系数,从而获得了整个时域和频域的完全响应。该文用这种外推方法分析计算了多导体柱的电磁散射。     

介质柱电磁极化散射的计算和分析

本文首次给出柱形体的一种有价值的极化散射矩阵Ｓ,定义,Ｓ,具有六个自由度,它包含了柱形体散射的所有信息,并给出计算平行极化ＲＣＳ的垂直极化ＲＣＳ等公式。从Ｓｓ也易于导出线极化基极化散射矩阵Ｓｔ和圆极化基极化散射矩阵Ｓｃ等。在此基础上本文将ＭｏＭ－ＣＧＭ－ＦＦＴ混降低了所需计算机内存和ＣＰＵ,提高了计算效率。本文以介质板柱体的极化散射为例进行了计算,所得结果与理论结果与及其它文献中的精确结果进行比较     

Protecting EFIE-based scattering computations from effects ofinterior resonances

A numerical method, based on the standard matrix formulation of the electric field integral equation (EFIE) for calculating the scattering from conducting bodies near resonant frequencies, is given for both stabilizing the numerical calculations and finding the form of the resonant fields. When this method is used along with a direct solution to the original matrix equation, it requires insignificant additional computation. An additional advantage of this approach is that it can easily be implemented in existing computer codes by using a single, standard but general, plug-in module     

目标电磁散射极点的不变性特征分析

对频域磁场积分方程在离散化的基础上进行了矢量分析，发现离散化后的矩阵方程中含有频率因子的算子矩阵仅包含了反映散射体形状的矢量信息，从而得出极点的分布只依赖于目标的外部形状信息这一结论；然后利用FDTD进行了仿真研究，从不同姿态角(散射方向)的后时响应数据中提取了极点，结果保持了较好的一致，进一步证实了目标姿态角的改变不会影响极点的分布这一特征。     

Computation of TM and TE modes in waveguides based on a surfaceintegral formulation

The surface integral formulation is used for the computation of TM and TE modes propagating in dielectric loaded waveguides. This formulation makes use of the surface equivalence principle whereby the field at any point internal or external to the waveguide can be expressed in terms of equivalent surface currents. This procedure reduces the original problem into a set of integro-differential equations which is then reduced to a matrix equation using the method of moments. The solution of this matrix equation provides the propagation characteristics of the waveguide and the equivalent surface currents existing on the waveguide walls. The equivalent surface currents can be used to compute the fields at all points, both inside and outside the waveguide. The surface integral method has been used to compute the propagation characteristics of waves propagating in dielectric loaded waveguides. The computed results agree very well with analytical and published data. A method that can be used to remove spurious modes is illustrated     

多重网格技术与波恩迭代法 相结合的反演新方法

本文将多重网格技术与波恩迭代法(BIM)相结合,利用时域散射数据对二维无耗非均匀介质剖面进行了反演.在反演迭代过程中,待反演目标区域的离散网格由粗逐渐变细.由于在反演的初期,目标区域离散网格较粗,离散反演积分方程所得到的矩阵方程的维数较小、条件数较低,使得该方法具有稳定性好、更容易收敛到真解的特点.通过反演实例表明,该方法极大地降低了反演过程的计算量,与传统的BIM方法相比能更精确地反演高对比度的散射目标.更为重要的是本文方法简单可行、可以与其它任何反演方法相结合.     

Electromagnetic scattering from ducts with irregular edges. I.Circular case

A formulation is developed for electromagnetic scattering from finite circular ducts terminated with irregular edges. The analysis is based on the solution of the electric field integral equation using an entire-domain Galerkin expansion for both the axial and the circumferential variation of the currents, defined in terms of an edge-slope-dependent vector field that provides simplifying symmetry properties for the method-of-moments system matrix. Comparisons are made with edge-slope-independent formulations. The analysis is general and applicable for cases in which the functional variation of the edge irregularities is specified by either a deterministic or a random process. Circumferential modal decoupling occurs when the irregularities are specified by a stationary stochastic process having a periodic correlation function. Numerical results are given for edge irregularities governed by a Gaussian random process and are compared for various limiting cases with results for right circular cylindrical ducts     

Numerical solution of integral equations for dielectric objects ofprismatic shapes

A numerical method to investigate scattering from dielectric geometries of prismatic shapes has been developed. The surface integral equations are formulated by Schelkunoff's equivalence principle in terms of equivalent surface electric and magnetic currents. To solve these integral equations for the unknown currents, the object's cross-section is mapped onto a circle. In the transformed space, Fourier type entire-domain basis functions are used in the cross section and triangular subdomain basis functions are selected along the generating curve to represent the currents. A moment method is then used to reduce the integral equations to a matrix equation to compute the current coefficients. It is found that the transformation of the object's surface to a circular shape improves the convergence of the current mode in the cross-section. However, the current modes are coupled on the surface and the matrix equation includes all the modes     

用时域积分方程法计算介质目标的电磁散射

本文应用时域积分方程法计算介质目标的散射场，并以球体和带球帽的圆柱体为例给出了沿轴向入射平面波的电磁散射结果，与实际测试结果非常一致，值得指出的是，虽然本文给出的介质目标具有平面对称性，但该方法适用于任意形状的目标。     

Integral equation analysis of artificial media

This paper presents an integral equation and method of moments (MM) solution to determine the effective permittivity and permeability of an artificial medium. The artificial medium is modeled as a triple infinite periodic array of identical scattering elements. A plane wave of unknown phase constant is assumed to propagate in the periodic medium in a given direction, and the periodic moment method (PMM) is used to set up a matrix equation for the currents on the center element of the periodic array. By setting the determinant of the PMM impedance matrix to zero, one can determine the phase constant of the plane wave, and then the effective permittivity and permeability of the artificial medium     

Studies on Fast Algorithm for the Scattering of a Large Array of Waveguide-Fed Wide-Slot Antennas in Millimeter Wave Region

We present an effective numerical technique to characterize the scattering of wide-slot antennas fed by waveguides with arbitrary terminations in terms of the method of moment (MoM) and the mixed potential integral equation (MPIE). In particular, the precorrected-fast Fourier transform (P-FFT) eliminates the need to generate and store the usual square impedance matrix andthus leads to speed up the matrix-vector multiplication in the resultant system. This property makes the Rao-Wilton-Glisson (RWG) functions to be useful in simulating electrically large-scale problems. In addition, the scattering from the finite ground surfaces is accounted for in the total scattered field by using the method of equivalent edge currents. The numerical results are presented and compared with both the traditional method of moment results obtained using the entire-domain basis functions and the experimental results, to demonstrate the proposed method to be a good candidate for study on the scattering of arbitrary wide-slot large array.     

Electromagnetic scattering from cylindrical arrays of infinitely long thin wires

Plane wave scattering by a cylindrical array of equally spaced infinitely long perfectly conducting thin wires is examined. The symmetry of the structure is exploited to derive a closed form expression for the currents excited on the wires, using the concept of circulant matrix and, alternatively, using a DFT (discrete Fourier transform) approach