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。     

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.     

高阶MoM及其与PO的混合法计算电磁散射问题

本文提出了一种新的以高阶矩量法(MoM)与物理光学法相结合的混合法(MoM-PO).该方法采用曲面参数化的离散方法,保证了建模的精确性.计算过程中将散射表面灵活划分为MoM区和PO区,在各自区域可以灵活确定离散单元的大小和密度.MoM区域的高阶矩量法,采用基于Lagrange插值的高阶矢量基函数,结合点匹配技术,比传统的高阶法简单,易于实现.计算结果表明,本文的高阶矩量法及其与物理光学法结合的混合方法能准确有效的计算目标的电磁散射特性.     

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.     

基于自适应积分法的三维目标电磁散射的研究

随着物体电尺寸不断变大,传统矩量法计算物体电磁散射和辐射会使计算量和存储量迅速的增加,最终导致无法计算出结果,而自适应积分法解决了矩量法计算量和存储量的问题,使得存储量变小,并利用快速傅里叶变换(FFT)加速了矩阵向量乘积,更加适用于求解电大尺寸的目标。     

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。     

预处理结合AWE技术求解导体目标RCS

采用渐近波形估计技术(AWE)和预处理技术求解导体目标的宽带雷达散射截面(RCS)。应用矩量法求解导体目标的电场积分方程,通过构造预条件算子,使由矩量法得到的阻抗矩阵稀疏化,从而计算导体表面电流时变得简便,再结合渐近波形估计(AWE)技术计算导体目标的宽带雷达散射截面(RCS)。实例结果表明,该方法在计算电大导体目标时具有较高的计算效率和很好的精度。     

多尺度问题电磁特性叠层矩量法分析北大核心CSCD

论文提出了一种叠层矩量法分析多尺度目标电磁特性。论文采用矩量法直接计算强相互作用区域,多层矩阵压缩方法(MLMCM)和多层快速多极子方法(MLFMA)分别用于加速计算低频和高频作用区域。论文通过使用多分辨ILU(MR-ILU)预条件加速迭代求解矩量法离散多尺度目标产生的病态矩阵方程。通过分析实际多尺度目标电磁特性证明论文方法的有效性。     

周期小波在电磁散射中的应用

讨论周期小波与矩量法相结合的方法在二维电磁散射计算中的应用，以周期小波作为基函数和权函数，并利用ｃｏｉｆｌｅｔ小波的消失矩性质，求解速度较快，结果非常精确。本文分别用小波矩量法、传统的矩量法及广义多极子方法计算了一个无限长方柱在平面波照射下的电流分布，并与有关资料上的结果进行比较，吻合得很好。     

任意形状单元有限微带阵列的电磁散射分析

提出一种有限微带阵列电磁散射特性分析的有效方法。该法采用有限阵格林函数与矩量法相结合的方法，有效地解决了矩量法在大型阵列电磁特性分析中的计算效率问题；通过选取RWG基函数，使该法适用于任何单元形状的微带阵列。文中计算了矩形、十字形及圆形单元微带阵列的雷达截面，并与常规矩量法和参考文献的计算结果进行了比对，验证了该方法的有效性。     

基于GA 与PIM 混合方法的基站天线波束赋形设计

基站天线的波束赋形设计是提高移动通信系统信道性能的关键技术之一。将投影迭代法和遗传算法应用到板状振子型基站天线的计算中,实现基站天线的快速优化设计。首先把振子形式假设为条带形状,对振子和底板均采用RWG基函数展开,得到传统矩量法的矩阵方程,然后通过投影迭代逐步修正未知电流,进而求得天线的远场方向图与天线尺寸的关系,最后与遗传算法相结合,优化设计了斜极化基站天线的波束赋形。实验结果与设计结果相吻合,证明了该方法的实用性。     

Computation of fields in an arbitrary shaped heterogeneousdielectric or biological body by an iterative conjugate gradient method

Electromagnetic (EM) fields in a three-dimensional, arbitrarily shaped, heterogeneous dielectric or biological body illuminated by a plane wave are computed by an iterative conjugate gradient method. The method is a generalized method of moments applied to the volume integral equation. Because no matrix is explicitly involved or stored, the method is capable of computing EM fields in objects an order of magnitude larger than those that can be handled by the conventional method of moments. Excellent numerical convergence is achieved. Perfect convergence to the result of the conventional moment method using the same basis and weighted with delta functions is consistently achieved in all the cases computed, indicating that these two algorithms (direct and iterative) are equivalent     

Analysis of low frequency scattering from penetrable scatterers

A method is presented for solving the surface integral equation using the method of moments (MoM) at very low frequencies, which finds applications in geoscience. The nature of the Helmholtz decomposition leads the authors to choose loop-tree basis functions to represent the surface current. Careful analysis of the frequency scaling property of each operator allows them to introduce a frequency normalization scheme to reduce the condition number of the MoM matrix. After frequency normalization, the MoM matrix can be solved using LU decomposition. The poor spectral properties of the matrix, however, makes it ill-suited for an iterative solver. A basis rearrangement is used to improve this property of the MoM matrix. The basis function rearrangement (BFR), which involves inverting the connection matrix, can be viewed as a pre-conditioner. The complexity of BFR is reduced to O(N), allowing this method to be combined with iterative solvers. Both rectilinear and curvilinear patches have been used in the simulations. The use of curvilinear patches reduces the number of unknowns significantly, thereby making the algorithm more efficient. This method is capable of solving Maxwell's equations from quasistatic to electrodynamic frequency range. This capability is of great importance in geophysical applications because the sizes of the simulated objects can range from a small fraction of a wavelength to several wavelengths     

二维电大导体目标宽带雷达散射截面的快速计算

在矩量法的基础上,应用空间分解技术将二维电大导体目标剖分成若干子区域,考虑子区域间的耦合,通过累进迭代法计算出目标表面电流,然后结合渐近波形估计技术计算了二维电大导体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.     

Matrix methods for field problems

A unified treatment of matrix methods useful for field problems is given. The basic mathematical concept is the method of moments, by which the functional equations of field theory are reduced to matrix equations. Several examples of engineering interest are included to illustrate the procedure. The problem of radiation and scattering by wire objects of arbitrary shape is treated in detail, and illustrative computations are given for linear wires. The wire object is represented by an admittance matrix, and excitation of the object by a voltage matrix. The current on the wire object is given by the product of the admittance matrix with the voltage matrix. Computation of a field quantity corresponds to multiplication of the current matrix by a measurement matrix. These concepts can be generalized to apply to objects of arbitrary geometry and arbitrary material.     

Calculation of electromagnetic waves scattering by non-homogeneous surface impedance using moment method

In this paper, using the method of moments to calculate the current density and mono-static and bi-static radar cross section of an unlimited strip by a non-homogeneous impedance. Here, incident wave is a plane wave. To authenticate the method, using the iterative method to solve the integral equations is engaged. Simulation results show that the surface with non-homogeneous impedance has reduced or increase in potential for bi- and mono-static radar cross section in certain azimuth.     

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     

埋于介质中的二维多导体目标的微波成象

提出了一种埋于介质体内多导体目标几何特性和物理特性重建的迭代方法。应用Ｎｅｗｔｏｎ－Ｋａｎｔｏｒｏｖｉｔｃｈ方法求解非线性方程组,得到关于目标特性矢量的Ｆｒｅｃｈｅｔ导数,从而使非线性方程转僳“线线性”＋“迭代”的处理过程。     

The Order-and-Type Prediction Problem Arising from Passive Intermodulation Interference in Communications Satellites

Intermodulation (IM) effects were recently observed in communications satellites where the source of nonlinearity was traced back to passive and normally linear components. This phenomenon is sometimes called passive intermodulation (PIM) and can cause serious interference to the ultrasensitive receiver on board the spacecraft. One interesting and important aspect of the PIM study is to find the order and type of IM products causing interference in an arbitrary satellite receive band. It is shown that the problem can be reduced by the use of number theory to a Diophantine optimization problem. Two types of tree searches are formulated and proposed as viable approaches. Some additional bounds for the equal-spacing case and an iterative technique for the unequal-spacing case are described. Finally, we show, by means of an example, that the proposed techniques offer a practical method of solving the order and type prediction problem.