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。     

基于Laguerre多项式的边界积分方程时域求解

针对时域积分方程中存在的晚时震荡问题,介绍了基于Laguerre多项式的电场、磁场和混合场积分方程,求解了导体球和导体圆柱的时域电流分布和后向散射场以及单站RCS。结果表明,3种积分方程很好地解决了晚时震荡问题,混合场积分方程具有更高的计算精度。     

基于Laguerre多项式的边界积分方程时域求解

针对时域积分方程中存在的晚时震荡问题,介绍了基于Laguerre多项式的电场、磁场和混合场积分方程,求解了导体球和导体圆柱的时域电流分布和后向散射场以及单站RCS。结果表明,3种积分方程很好地解决了晚时震荡问题,混合场积分方程具有更高的计算精度。     

ACA 算法加速时域MoM 分析瞬态电磁问题

本文使用自适应交叉近似算法(Adaptive Across Approximation)加速时域积分方程的求解,从而达到降低内存 使用量和缩短计算时间的目的。众所周知,基于时间步进(Marching-On-in-Time)的时域积分方程的解会在时间轴后半 部分出现明显的震荡现象,造成解的不稳定。阶数步进(Marching-On-in-Degree)是解决这一问题的有效途径。因此, 本文首先采用MOD 方法求解时域积分方程,从而得到一个时间轴上稳定的解;其次,由于时域矩量法产生的大规模 稠密矩阵,其求解势必对内存以及硬件资源有着较高的要求。ACA 算法是一种纯数学加速方法,本文将它应用于时 域积分方程的求解过程中,有效地降低了资源需求。最后,通过算例验证了本文方法的有效性和可行性。     

一种改进的时间步进稳定性平均方法

介绍了时域积分方程方法（TDIE）的基本原理,提出一种抑制时域电场积分方程（TDIE）时间步进（MOT）后期振荡的新平均算法,提高了MOT算法后期的稳定性。计算了高斯脉冲波照射到金属立方体时目标表面的电流响应,数值结果表明,该方法简单有效地推迟了TDIE后期震荡时间。     

电磁脉冲下螺旋天线瞬态响应的仿真研究

由于通信天线经常工作在宽带或者多频带模式,为了对电磁干扰下的通信天线进行保护,对天线时域特性的仿真必不可少.其中一个需要研究的问题就是将天线装载于金属平台上并同时使用脉冲源激励.文中使用一种具有通用性的数值方法--时域电场积分方程,仿真了电磁脉冲照射下螺旋天线的宽带瞬态响应特性.采用拉革尔多项式作为全域时间基函数来展开时间变量,获得求解线天线散射辐射问题的时域电场积分方程,也就是阶数步进递推格式,最后使用数值计算得到了螺旋天线的瞬态响应特性.     

多项式建模解电离层相位污染阶数选择新方法

电离层相位污染使天波超视距雷达杂波频谱展宽,影响舰船等低速目标检测.针对这一问题,近年来发展了基于分段多项式相位建模和高阶模糊函数的(HAF)解电离层污染算法,如何合理地选取模型阶数是该算法的核心.给出了两种改进的自适应多项式建模阶数选择方法.并利用仿真方法进行了验证,结果表明:基于高阶模糊函数变换性质的频域和时域阶数选择方法的计算量较现有算法有较大提高,且频域法可在较低信噪比下准确判断多项式阶数.     

基于栅瓣修正窗的调频步进信号时域合成算法

文章针对调频步进信号存在频域冗余时,"去斜"接收距离像时域合成算法出现的栅瓣现象,提出基于栅瓣修正窗的时域拼接算法。根据本雷达收发分置的特点,提出利用发射信号直接衰减回环到接收端的信号形成理想栅瓣修正窗的方法;给出基于栅瓣修正窗的时域拼接算法流程及仿真验证;利用某近场成像雷达的实测数据验证了本方法的有效性。对调频步进信号的实际工程应用具有一定的参考价值。     

时域积分方程MOT算法的推迟位时间卷积数值积分新方法

通过变量代换平滑三角形上推迟位（标量位函数和矢量位函数）并消除推迟矢量位旋度的奇异性,使得采用数值积分法就能够精确快速地计算任意正则时间基函数与推迟位函数及推迟矢量位旋度之间的时间卷积运算,可用于基于任意类型时间基函数的时域电场、时域磁场及其混合场积分方程时间步进（MOT ）算法。与时间卷积运算的解析法对比分析表明,该时间卷积数值积分方法能够精确快速地计算基于任意类型时间基函数和不同时间步长条件下时域积分方程MOT算法的阻抗矩阵元素;而具体的计算实例也表明,阻抗矩阵的精确计算显著地提升了时域积分方程MOT算法的后时稳定性和求解精度。     

空间光调制器产生拉盖尔-高斯光束方法研究

为了解决产生拉盖尔-高斯模式光束较难的问题,采用二进制振幅全息图方法,基于空间光调制器,产生了拉盖尔-高斯光束,进行了理论分析和实验验证。推导了高斯光束到拉盖尔-高斯光束傅里叶变换的传递函数,通过对拉盖尔-高斯模拟图的修正,得出了可以用于空间光调制器的二进制全息图; 搭建了基于4f系统的实验平台,取得了不同阶数的拉盖尔-高斯模式输出,并在实验中对产生的拉盖尔-高斯光束进行了检测。结果表明,此套装置搭建及操作简便,且可实现动态可控的光束输出,对于产生高阶涡旋光束以及因斯-高斯模式都有重要意义。     

Transient electromagnetic scattering from dielectric objects using the electric field Integral equation with Laguerre polynomials as temporal basis functions

In this paper, we propose a time-domain electric field integral equation (TD-EFIE) formulation for analyzing the transient electromagnetic response from three-dimensional (3-D) dielectric bodies. The solution method in this paper is based on the Galerkin's method that involves separate spatial and temporal testing procedures. Triangular patch basis functions are used for spatial expansion and testing functions for arbitrarily shaped 3-D dielectric structures. The time-domain unknown coefficients of the equivalent electric and magnetic currents are approximated using a set of orthonormal basis function that is derived from the Laguerre functions. These basis functions are also used as the temporal testing functions. Use of the Laguerre polynomials as expansion functions for the transient portion of response enables one not only to handle the time derivative terms in the integral equation in an analytic fashion but also completely separates the space and the time variables. Thus, the time variable along with the Courant condition can be eliminated in a Galerkin formulation using this procedure. We also propose an alternative formulation using a different expansion of the magnetic current. The total computational cost for this new method is similar to that of an implicit marching-on in time (MOT)-EFIE scheme, even though at each step this procedure requires more computations. Numerical results involving equivalent currents and far fields computed by the two proposed methods are presented and compared.     

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     

Use of the pattern equation method for solution of problems of scattering of electromagnetic waves by bodies covered with a dielectric

The pattern equation method is generalized to problems of scattering of electromagnetic waves by 3D perfectly conducting bodies covered with a dielectric. The method is implemented in an algorithm for bodies of a rather arbitrary shape. In the case of a sphere, explicit analytic expressions for the coefficients involved in the scattering pattern are obtained from the general system of equations for these coefficients. The expressions obtained coincide with the corresponding formulas in the theory of Mie series. Scattering patterns are calculated for various bodies of revolution. The calculation results for bodies with a coating are compared to similar characteristics obtained via simulation of a dielectric coating with the suitable impedance.     

Treating the instabilities in marching-on-in-time method from adifferent perspective [electromagnetic scattering]

A general method is presented to treat the instabilities which are frequently observed in the electromagnetic transient solutions using the marching-on-in-time method. The basic idea is to apply an finite impulse response (FIR) filter with a constant group delay during the course of marching-in-time. An electric field integral equation (EFIE) formulation for perfectly conducting bodies is used as a vessel to demonstrate the method. Sample numerical results are presented and discussed. The computed results, while showing good agreement with the data obtained from other methods, present great stability improvement     

精确稳定求解时域电场积分方程的一种新方法

时域电场、磁场和混合场积分方程已被广泛用来分析散射体的时域散射响应.基于适当的空间积分方法和隐式的时间步进算(MOT)法在求解时域磁场和混合场积分方程时总是稳定的,然而在求解TDEFIE时则是不稳定的.在本文中,时域电场积分方程的非奇异性积分采用标准的高斯求积法来计算;而利用参数坐标变换和极坐标变换将其奇异性积分转换成为可以分区域精确快速计算的非奇异性积分.通过数值实验表明,利用该方法可以非常精确稳定地求解时域电场积分方程,即使是在时间迭代后期也不必采用任何求平均的过程;另外,该方法可以用于任意时间基函数并可以推广到高阶空间基函数的情形.     

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.     

A hybrid FEM/MOM technique for electromagnetic scattering andradiation from dielectric objects with attached wires

A hybrid formulation is presented, which combines the method of moments (MOM) with the edge-based vector finite element method (FEM) to solve electromagnetic radiation problems from structures consisting of an inhomogeneous dielectric body of arbitrary shape attached to one or more perfectly conducting bodies. While either method alone fails to model these structures efficiently, a combination of both finite element and moment methods provides an excellent way to solve these problems. The FEM is employed to handle the interior domain of inhomogeneous dielectric bodies and the method of moments is used to develop surface integrals that relate the field quantities on boundary surfaces with the equivalent surface currents. These integral equations are then coupled to the finite element equations through the continuity of the tangential magnetic fields across the hybrid boundaries     

Study of mixed-order basis functions for the locally corrected Nystro/spl uml/m method

A high-order locally corrected Nystro/spl uml/m (LCN) method employing the mixed-order basis functions proposed by C$80al/spl iota/s$80kan and Peterson is presented for the electromagnetic scattering by targets composed of both dielectric and conducting bodies. An integral operator based on a combined field formulation for conducting surfaces and a Mu/spl uml/ller formulation for dielectric surfaces is used. It is found that for general scattering objects, mixed-order basis functions accelerate the convergence of the LCN solution, can eliminate spurious charges, and can significantly reduce the condition number of the impedance matrix.