解决电大尺寸电磁场问题的改进矩量法研究

首先介绍基于积分方程的矩量法原理及其特点.基于传统矩量法在解决电大尺寸电磁场问题上的局限性,分析几种典型的改进矩量法,包括快速多极子方法、小波矩量法、混合算法和自适应积分法.几种方法通过不同的途径减小了计算量,所以将几种方法结合起来使用,可以有效地解决电大尺寸电磁场问题.运用改进的矩量法,突破了传统矩量法解决电大尺寸电磁场问题的局限性.     

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。     

混合ACA和MLFMA方法计算复合目标电磁散射

采用矩量法(MoM)计算电大尺寸的复合目标的电磁散射。为了能够高效快速地计算电大尺寸三维复合目标的电磁散射,提出一种新的混合方法,将自适应交叉近似(ACA)算法和多层快速多级子(MLFMA)算法相结合,共同加速矩量法的计算。其中,MLFMA用于加速目标与自身的作用,ACA用于加速目标与其他目标的相互作用。提出的混合算法在计算复合目标电磁散射时,可降低运算存储,缩短阻抗矩阵填充时间,并且能够加快矩阵矢量乘,且不影响计算精确度。数值算例表明,所提快速算法能够在保证电磁散射计算精确度前提下,比传统方法更高效。     

多层自适应交叉近似加速的旋转对称体矩量法

为了更有效地分析旋转对称电大物体的电磁散射问题,提出了一种针对旋转对称矩量法的多层自适应交叉近似加速方法,并分别应用于基于三角形基函数和3阶Hermite基函数的旋转对称矩量法.使用所提方法加速混合场积分方程下旋转对称体矩量法的单模式与多模式阻抗矩阵的构建过程时,计算得到的远场雷达散射截面积与传统旋转对称矩量法的结果吻合良好,且计算效率明显提高.     

电大目标瞬态散射的时域自适应积分算法

为降低时域积分方程(TDIE)计算电大目标瞬态散射时的计算量和内存需求,研究了时域自适应积分算法(TDAIM).基于TDAIM的单元分组思想,给出了目标瞬态散射的计算流程,并在.Net平台下对典型目标进行了编程实现.在此基础上,针对球锥体和舰船等典型目标进行了仿真.仿真结果表明:本文实现的时域自适应算法与矩量法(MOM...     

用AIM快速计算电大尺寸物体的散射特性

如果使用传统的矩量法计算电大尺寸物体的电特性,需要很大的存储量和计算量,本文采用AIM(自适应积分方法)减少所需的存储量和计算量。使用AIM计算了导体平板的RCS,与传统的矩量法相比大大减少了计算时间和存储量,显示了AIM在计算电大目标特性时的优越性。     

求解多尺度目标电磁散射的积分方程快速算法

多层快速卡特森展开算法(Multilevel Accelerated Cartesian Expansion Algorithm,MLACEA)可用于加速电小尺寸结构积分方程矩量法,且矩阵与矢量乘积运算计算复杂度为O(N)量级;MLACEA和多层快速多级子算法(Multilevel Fast MultipoleAlgorithm,MLFMA)均基于八叉树分组结构,便于实现它们的混合快速算法MLA-CEA-MLFMA.该混合算法可大幅度降低模拟合精细结构的电大尺寸目标宽带电磁散射问题的计算复杂度.还详细阐述了求解电场积分方程的MLACEA算法及其与MLFMA算法的混合快速算法MLACEA-MLFMA算法;并通过计算实例对比分析了MLFMA算法与MLACEA-MLFMA混合算法的计算效率.     

求解IETD问题的CFIE方程之比较

针对基于矩量法的积分方程时域求解存在的晚时震荡问题,分析两种稳定求解时域积分方程的混合场积分方程方法:隐式时间步进算法的混合场积分方程和基于拉盖尔多项式阶数步进算法的混合场积分方程。计算了目标的时域散射场和单站雷达散射截面,两种方法求得的结果吻合较好,表明两种方法解决时域积分方程晚时震荡问题的有效性。     

使用AIM快速计算微带阵列的电特性

巨大的存储量和计算量通常使得矩量法无法分析大型微带阵列天线的电特性,而自适应积分方法(AIM)能够大大减少矩量法需要的存储量和计算量。该文使用AIM计算了微带贴片阵列的散射特性和微带阵列天线的辐射特性。计算结果显示: AIM能够以较少的存储量快速得到微带阵列的电特性。     

应用切比雪夫逼近快速求解目标宽带雷达散射截面

将切比雪夫逼近理论应用于目标宽带电磁散射特性分析中,通过求解给定频带内的切比雪夫节点和节点处的目标表面电流,实现了频带内任意频率点表面电流的快速预测,从而实现目标宽带雷达散射截面的快速计算.组合场积分方程的使用消除了内谐振问题.将计算结果与传统矩量法逐点计算的结果进行了比较,结果表明在不影响精度的前提下,该方法的计算效率大大提高.     

Analysis of transient scattering from composite arbitrarily shapedcomplex structures

A time-domain surface integral equation approach based on the electric field formulation is utilized to calculate the transient scattering from both conducting and dielectric bodies consisting of arbitrarily shaped complex structures. The solution method is based on the method of moments (MoM) and involves the modeling of an arbitrarily shaped structure in conjunction with the triangular patch basis functions. An implicit method is described to solve the coupled integral equations derived utilizing the equivalence principle directly in the time domain. The usual late-time instabilities associated with the time-domain integral equations are avoided by using an implicit scheme. Detailed mathematical steps are included along with representative numerical results     

Solution of combined-field integral equation using multilevel fastmultipole algorithm for scattering by homogeneous bodies

We present an accurate method of moments (MoM) solution of the combined field integral equation (CFIE) using the multilevel fast multipole algorithm (MLFMA) for scattering by large, three-dimensional (3-D), arbitrarily shaped, homogeneous objects. We first investigate several different MoM formulations of the CFIE and propose a new formulation, which is both accurate and free of interior resonances. We then employ the MLFMA to significantly reduce the memory requirement and computational complexity of the MoM solution. Numerical results are presented to demonstrate the accuracy and capability of the proposed method. The method can be extended in a straightforward manner to scatterers composed of different homogeneous dielectric and conducting objects     

Electromagnetic Scattering by Arbitrarily Shaped PEC Targets Coated with Anisotropic Media Using Equivalent Dipole-Moment Method

The equivalent dipole-moment method (EDM) is extended and applied in the analysis of electromagnetic (EM) scattering by arbitrarily shaped perfect electric conductor (PEC) targets coated with electric anisotropic media in this paper. The scattering targets are discretized into tetrahedral volume elements in the material region and into triangle patches on the conducting surface, where the volume-surface integral equation (VSIE) is set up. Then the method of moments (MoM) is employed to solve the VSIE. In the impedance matrix, the near field interaction elements are computed by the conventional MoM while the far field interaction elements are modeled by the EDM. The proposed approach is sufficiently versatile in handling arbitrarily shaped objects coated with general electric anisotropic media and is easily constructed through a simple procedure. Numerical results are given to demonstrate the accuracy and efficiency of this method.     

一种分析复杂导体目标瞬态特性的快速方法

将渐进波形估计技术引入到频域矩量法中,并结合傅立叶逆变换和自适应复频率跳跃技术,快速而准确地分析任意形状导体目标的瞬态特性,大大提高了计算效率.在分析中,脉冲波形和导体目标的几何形状可以任意.分别以理想导体方形平板、理想导体立方体、理想导体球体和理想导体锥体为例,并将计算结果与频域矩量法的结果进行了比较.它们之间良好的一致性说明了所提出方法的正确性和有效性.     

任意形状导体目标的极点求解

从理论上求解极点,频域矩量法结合围线积分是通用且准确的方法,但由于计算量大而一直用于处理旋转对称目标的求解.本文提出Chebyshev多项式展开格林函数的方法,把频率因子从电场积分方程中分离出来,实现了多频点矩量法的快速计算,解决了任意形状导体目标极点的求解问题.最后对围线积分方法进行适当改进,并求解了三种目标的极点.     

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     

An Efficient Volume Integral Equation Solution to EM Scattering by Complex Bodies With Inhomogeneous Bi-Isotropy

A generalized volume integral equation method is formulated for electromagnetic scattering by arbitrarily shaped complex bodies with inhomogeneous bi-isotropy. Based on the volume equivalence principle, the integral equations are represented in terms of a pair of coupled bi-isotropic polarized volume electric and magnetic flux densities. Reduction of the integral equations into the corresponding matrix equations is obtained using the method of moments (MoM) combined with the tetrahedral mesh. In the MoM solution, the three-dimensional solenoidal function is incorporated as the basis function defined over each tetrahedral element and the details of implementation, particularly the treatment of integral singularities, will be elucidated. The efficiency and accuracy of the proposed method are validated by illustratively supported examples.     

Fast Analysis of RCS Over a Frequency Band Using Pre-Corrected FFT/AIM and Asymptotic Waveform Evaluation Technique

The pre-corrected fast Fourier transform (PFFT)/adaptive integral method (AIM) is combined with the asymptotic waveform evaluation (AWE) technique to present fast RCS calculation for arbitrarily shaped three-dimensional PEC objects over a frequency band. The electric field integral equation (EFIE) is used to formulate the problem and the method of moments (MoM) is employed to solve the integral equation. By using the AWE method, the unknown equivalent current is expanded into a Taylor series around a frequency in the desired frequency band. Then, instead of solving the equivalent current at each frequency point, it is only necessary to solve for the coefficients of the Taylor series (called “moments”) at each expansion point. Since the number of the expansion points is usually much smaller than that of the frequency points, the AWE can achieve fast frequency sweeping. To facilitate the analysis of large problems, in this paper, all the full matrices are stored in a sparse form and the PFFT/AIM method is employed to accelerate all the matrix-vector products on both sides of the matrix equation for the moments. Further, the incomplete LU preconditioner is used at each expansion point to improve the convergence behaviour of the matrix equation for the moments. The present method can deal with much larger problems than the conventional MoM-AWE method since the PFFT/AIM achieves considerable reduction in memory requirement and computation time. Numerical results will be presented to show the efficiency and capability of the method.      

一种稳定的时域电场积分方程求解方法

提出了一种求解任意形状理想导体目标时域散射的稳定时域电场积分方程(TDIE)方法,此方法能非常有效地消除后期振荡。利用显式MOT方法求解二阶时间微分的电场积分方程,矢量位随时间的变化关系采用边缘中心近似,标量位随时间的变化关系则采用三角面元重心近似,然后运用先五步后三步的平均方法。数值结果表明,本文方法能够有效地提高TDIE方法的收敛性和稳定性。