用MEI—FD方法分析Chiral媒质的电磁散射问题

本文应用不变性测试方程和有限差分方法分析Ｃｈｉｒａｌ媒质的电磁散射问题。应用该方法时，要在所讨论的区域内建立起一组有关电场和磁场的耦合差分方程，并且要在截断边界上应用不变性测试方程建立起有关边界点系数的方程。文中给出了一些非均匀、有耗且具有电大尺寸任意横截面Ｃｈｉｒａｌ柱的雷达散射截面的数值结果。     

迭代不变性测试方程法在城市微小区电波传播预测中的应用

本文建立了基于不变性测试方程法的二维城市微小区电波传播预测模型。该模型考虑了地面反射和建筑物墙面的二维散射,利用ＭＥＩ方法在每个建筑物表面建立共形差分网格形成差分方程,并用迭代方法模拟电波在建筑物之间的多次散射。所得结果与实测值ＧＴＤ,ＦＤＴＤ的预测结果进行了比较。     

用FD－MEI计算横各向异性媒质柱的电磁散射特性

本文推导了二维横各向异性媒质中电磁散射的差分方程，得到了９点的差分格式，并将不变性测试方程与该差分方程结合计算了具有任意横截面、非均匀、有耗和一般张量形式的二维横各向异性媒质柱的电磁散射。文中给出一些典型数值算例。数值结果表明，该方法在分析计算此类问题时是有效的且具有一定的优势。     

用FD—MEI计算横各向异性媒质柱的电磁散射特性

本文推导了二维横各向异性媒质中电磁散射的差分方程，得到了９点的差分格式，并将不变性测试方程与该差分方程结合计算了具有任意横截面，非均匀，有耗和一般张量形式的二维向异性媒质柱的电磁散射，文中给出了一些典型数值算例，数值结果表明，该方法在分析计算此类问题时是有效的且具有一定的优势。     

用MEI方法计算电大尺寸非均匀各向异性涂覆媒质导体柱

本文运用有限差分技术，构造出非均匀各向异性媒质曲边网格的五点差分方程，借助不变性测试方程（ＭＥＩ）这一新概念，成功地计算了电大尺寸任意厚度涂覆媒质的导体柱的ＲＣＳ特性。在截断边界上采用ＭＥＩ方程，使得截断边界十分接近散射体表面，从而使计算占用计算机的内存大大减少，同时与矩量法相比，还显著缩短了计算时间。本文在微机上计算的电大尺寸柱体周长达１２０个小长，是一般方法无法比所的。     

基于MEI吸收边界条件的导体柱散射问题模拟

首次在圆柱坐标系时域有限差分 (FDTD)法中采用基于时域不变性测试方程 (MEI)方法的吸收边界条件 ,对导体圆柱的电磁散射问题进行了数值模拟研究。在相同计算条件下 ,与应用Bayliss Turkel二阶辐射边界条件的FDTD结果相比较 ,直观地表明MEI方法结果与解析解吻合更好     

非均匀介质多柱体散射的计算

本文运用迭代MEI过程对非均匀介质柱的多柱体散射进行了计算。该迭代过程充分运用了不变性特点，使MEI方程在各次迭代中反复使用，不仅减少了计算量也大大减少了所需的内存空间．对于不规则网格剖分下有限差分方程的建立，则采用了一种广义的测试系数的方法。文中将均匀介质多柱体散射作为非均匀情况之特例，与已有结果作了对比，获得良好的一致性。对非均匀介质柱的计算，也提供了算例。     

一种有效的吸收边界条件及其在散射问题中的应用

本文推导了非均匀各向异性媒质的有限差分方程,通过改变参数可以使该差分方程适用于均匀、非均匀、各向同性或各向异性等各种情况下柱体的散射计算.文中还给出了一种新的吸收边界条件,并与不变性测试方程法和矩量法在计算时间、存贮空间方面进行了比较.结果表明:运用这个条件在计算时间和存贮空间上都具有优点,是计算电大尺寸媒质柱体电磁散射特性的一种有效手段.     

差分GPS着陆系统动态数据的测试与分析

ＤＧＰＳ／ＲＡ／ＮＬＣ系统是六一五所研制的差分ＧＰＳ精密进折着陆试飞验证系统，系统设计要求满足国际民航组织的Ｉ类精密进近要求，飞行试验研究院为ＤＧＰＳ／ＲＡ／ＮＬＣ系统的飞行试验建立了完整的测试设备与试飞方法。根据ＤＧＰＳ／ＲＡ／ＮＬＣ系统的试飞要求，选择了相应的测量基准设备和数据采集系统，定量地测量差分ＧＰＳ着陆系统在飞行状态下的定位精度。     

快速MEI算法及其在电大尺寸电磁散射问题中的应用

本文基于不变性测试方程法（ＥＭＩ）提出一种快速算法,在二维散 表面建立菜形差分网格后,通过对节点的重新排序,将原问题中的稀疏矩阵变换为带状稀疏阵,从而使占用的计算机内存和计算时间均由Ｏ（Ｎ２）下降为Ｏ（Ｎ）,可以解决原来无法计算的问题,议事 成功地计算了最大周长为１００００个波长的几个电大尺寸二维柱体的电磁散射,并与矩量法、ＭＥＩ方法进行比较。     

Electromagnetic scattering from a chiral cylinder-general case

A generalized finite-difference (FD) scheme combined with the measured equation of invariance (MEI) is presented for the analysis of electromagnetic scattering from an inhomogeneous and lossy chiral cylinder with electrically large, arbitrarily shaped cross section. A new FD mesh in both chiral and achiral regions is formed, and the FD equations in a chiral medium are derived; then a large sparse matrix is formulated. The numerical results of bistatic scattering width (two-dimensional radar cross section) are given for the chiral cylinders of rectangular, elliptical, and complex cross section, respectively. Some results are compared with available data     

Scattering by a chiral cylinder of arbitrary cross section

An integral equation and method-of-moments (MM) solution to the problem of scattering by an inhomogeneous chiral cylinder of arbitrary cross section is presented. The volume equivalence theorem for chiral media is developed and used to formulate a set of coupled integral equations for the electric and magnetic volume polarization currents representing the chiral cylinder. These coupled integral equations are solved using a standard pulse basis and point-matching MM solution. Numerical results, including echo width and internal fields, are presented for the scattering by chiral slabs and circular cylinders. These results are compared to exact solutions when available     

时域有限面积法解手征介质涂层导体柱的电磁散射

本文将时域有限面积法推广应用于研究任意截面复合手征介质涂层导体柱的电磁散射问题,建立了数值求解复合手征介质问题的时域基本方程.本文使用正交贴体计算网格,并选用适合正交曲线坐标系的二阶精度吸收边界条件,提高了计算精度.对典型的复合手征介质涂层导体柱的RCS计算表明,数值计算结果与级数解相吻合.     

On the numerical errors in the 2D FE/FDTD algorithm for different hybridization schemes

Numerical experiments are carried out to study the accuracy of the two-dimensional Finite-Element/Finite-Difference Time-Domain (FE/FDTD) hybrid algorithm with three different hybridization schemes. The physical space is split into two domains viz., the finite difference (FD) and finite element (FE) domains. In the FD domain, a uniform Cartesian grid is used and in the FE domain, triangular elements with edge vector basis functions are used. Newmark-/spl beta/ scheme is used for temporal discretization in the FE domain. The unphysical reflections introduced by the FE domain for the different schemes are compared by computing the 2-D radar cross section of the FE domain surrounded by the FD domain. Computed results of scattering by a PEC circular cylinder for TE/sub z/ incidence using the three schemes and the traditional FDTD algorithm are presented.     

手征涂覆球对高斯波束的散射

在广义米理论的基础上,通过把入射高斯波束、散射场和内部场用适当的球矢量波函数展开,给出了一种求解手征涂覆球对高斯波束散射的解析方法。待定的展开系数可由从边界条件得到的线性方程组求出。对于波束的区域近似模型,给出了微分散射截面的数值结果。结果表明：与介质涂覆的情况相比,手征涂覆对微分散射截面和散色场的极化特性都产生了较大的影响。     

Radar cross-section study of cylindrical cavity-backed apertureswith outer or inner material coating: the case of E-polarization

A dual-series-based solution is obtained for the scattering of an E-polarized plane wave from a cavity-backed aperture which is formed by a slitted infinite circular cylinder coated with absorbing material. The material coating can be done on the inner or outer surface of the cylinder. For both cases, numerical results are presented for the radar cross section and comparisons are given for two different realistic absorbing materials. The radar cross-section results are also given for the aspect angle of the screen. Finally, the dependence of radar cross section on the thickness of the absorbing layer is presented     

Backscatter RCS for TE and TM excitations of dielectric-filledcavity-backed apertures in two-dimensional bodies

Transverse electric (TE) and transverse magnetic (TM) scattering from dielectric-filled, cavity-backed apertures in two-dimensional bodies are treated using the method of moments technique to solve a set of combined-field integral equations for the equivalent induced electric and magnetic currents on the exterior of the scattering body and on the associated aperture. Results are presented for the backscatter radar cross section (RCS) versus the electrical size of the scatterer for two different dielectric-filled cavity-backed geometries. The first geometry is a circular cylinder of infinite length which has an infinite length slot aperture along one side. The cavity inside the cylinder is dielectric filled and is also of circular cross section. The two cylinders (external and internal) are of different radii and their respective longitudinal axes are parallel but not collocated. The second is a square cylinder of infinite length which has an infinite length slot aperture along one side. The cavity inside the square cylinder is dielectric-filled and is also of square cross section     

A scattering model for thin dielectric cylinders of arbitrary crosssection and electrical length

A scattering solution for long, thin, dielectric cylinders of arbitrary cross section and electrical length is presented. The infinite-cylinder scattering formulation is shown to be an asymptotic solution for the finite-cylinder case, regardless of cylinder electrical length or cross section. The generalized Rayleigh-Gans (GRG) approximation for circular cylinders is shown to be a specific case of this general formulation, and therefore, the assertions of GRG are explicitly proven. A moment-method (MM) solution for thin circular cylinders is likewise presented and is used to examine and quantify the asymptotic errors associated with this solution     

The scattering cross section of a composite cylinder, geometric optics

The optical analogue of the scattering cross section of a composite cylinder is developed from a representation of the forward scattered amplitude as a continuous spectrum of radial eigenfunctions. The Debye approximation for the Hankel functions, which is valid when their arguments are large compared to the order, leads to a series of integrals which can be evaluated asymptotically by the method of stationary phase. The final result, for a certain range of parameters, is a diffraction correction plus a double sum of terms, each of which can be interpreted as an optical ray. It is shown that if the angular displacement between the incoming and scattered ray directions is(2m + 1)pi, the ray must have been reflected at the conducting core of the cylinder at least2m + 1times. After the parameter ranges to which these results apply were determined, the nonlinear equations for the ray angles were solved on a large-scale digital computer and the scattering cross section of a number of composite cylinders was calculated as a function of frequency. The results are presented graphically.     

基于奇异值分解的方法求解目标内谐振时的散射截面

表面积分方程已被广泛地用来分析电磁散射问题,但在离散的内谐振频率点上,用矩量法求解积分方程将得到错误的结果.本文基于电场积分方程,应用奇异值分解找出谐振模电流,并采用正交化方法将其舍去,从而得到非谐振模电流的分布.文中计算了一无限长理想导体圆柱内谐振时的散射截面,所得结果与解析解一致,并对一无限长理想导体三角柱的前向散射截面进行了计算,结果表明本文方法是有效和准确的.