快速计算地面上车辆目标的电磁散射特性

为快速计算地面上车辆目标的电磁散射特性,实现适用于半空间环境的多层快速多极子方法.对于近区项,利用严格的半空间并矢格林函数进行计算;对于远区项,首先将半空间格林函数分解为直射项和反射项,然后采用实镜像方法计算反射项.方法物理概念清晰,与目前常用的离散复镜像方法相比,具有良好的收敛性和稳定性,大大降低计算时间和内存需求.实例计算并分析地面上汽车模型的电磁散射特性.     

一维周期结构散射近-远场外推的两种方法

 首先讨论了自由空间中一维周期结构近-远场外推的Floquet模方法,即对FDTD计算所得散射近场中输出边界上散射场进行级数展开,求出各阶Floquet模的复数幅值,再求得远区场。接着介绍了求解一维周期结构远区散射场的周期Green函数方法,即根据FDTD计算所得散射近场中输出边界上散射场,求得等效面电磁流后,再借助周期Green函数进行外推得到远区场。两种方法均仅用一个周期单元内的散射近场进行外推。计算结果验证了上述两种方法外推的有效性。     

考虑棱边散射的半空间复杂导体目标高频分析方法

研究了半空间内复杂导体目标棱边散射的高频求解方法.分析半空间电磁波的传播规律和复杂目标棱边的电磁散射特性,将半空间并矢格林函数引入等效电磁流方法中,给出了基于等效电磁流法和物理绕射理论的半空间棱边散射场计算式,同时结合图形电磁学,对半空间复杂目标进行消隐处理,判断目标的棱边像素及获得棱边参数,与半空间目标的面元散射场相叠加,快速有效地计算了半空间复杂目标的雷达散射截面.数值结果证明了方法的有效性和准确性. 关键词： 半空间等效电磁流方法 半空间并矢格林函数 图形电磁学 雷达散射截面     

互易定理计算分层半空间上方任意取向偶极子的远区场

利用互易定理推导了考虑直达波和界面反射波时半空间分层界面上任意取向偶极子在上半空间远区辐射场的解析表达式. 进一步考虑电偶极子距离分界面为某一高度情形, 在考虑直达波和反射波程差基础上导出相应辐射场公式. 辐射场解析表达式中分层半空间TM和TE波反射系数可以通过连分数方法或传播矩阵法计算获得. 本文推导过程物理概念清晰, 所得解析结果适于计算观察点远离界面情形下偶极子的远区辐射场. 数值计算结果表明, 利用本文结果可以快速分析半空间上方任意取向偶极子的远区辐射场.     

离轴球形粒子对高斯波束的散射光通量的计算

利用矢量球谐函数展开的方法,研究了离轴球形粒子对椭圆高斯波束的散射。根据其远区散射场的形式,得出了归一化散射场的斯托克斯参量(散射强度)与颗粒直径、折射率以及散射角的关系。建立了计算离轴球形粒子对高斯波束散射通量的解析模型,计算了散射光在任意散射方向上的光通量,得到了前向任意立体角内散射通量的计算公式,为激光散射探测提供了理论依据。     

厄米-高斯光束对手征介质球的远场散射

利用复源点方法将厄米-高斯光束展开为球矢量波函数的形式。基于广义洛伦兹米氏理论,应用手征介质球与自由空间分界面处电磁场切向连续的边界条件以及球矢量波函数的正交性,得到手征介质球远区散射场展开系数。研究了厄米-高斯光束对手征介质球的散射特性。数值计算了厄米-高斯光束对手征介质球的远区散射场分布,分析了波束模式、手征参数和手征球尺寸等对散射特性的影响。     

有耗半空间上方导体目标电磁散射的多层快速多极子算法

提出基于高阶拟合的多层快速多极子算法,用于分析有耗半空间上方导体目标的电磁散射.采用高阶拟合方法将远区相互作用单元的半空间空域格林函数用级数表示,对高阶拟合项作加法定理展开,进而应用多层快速多极子算法.该方法具有分组小,内存需求低,易于实现的优点.用数值算例验证其正确性与有效性.     

基于新型混合场积分方程的半空间三维均匀介质目标电磁散射分析

利用介质半空间格林函数,将一种混合场积分方程(JMCFIE)推广应用到有耗半空间的均匀介质的散射分析中,以减少离散矩阵方程迭代求解时所需的迭代步数,提高矩量法(MoM)对半空间介质目标散射分析的求解效率.数值算例验证了方法的准确性和有效性.     

半空间电大涂敷目标散射的高频分析方法

研究了半空间内(海面,地面)电大尺寸涂敷目标散射的高频求解方法.将半空间并矢格林函数引入物理光学方法中,对半空间复杂环境影响进行考虑,并利用阻抗边界条件考虑涂敷目标表面的复杂电磁散射,推导出半空间物理光学分析方法,同时结合图形电磁学,对半空间电大涂敷目标进行消隐判断,提取像素面元法矢量和深度缓存等有效信息,快速有效地计算了半空间电大涂敷目标的雷达散射截面.数值结果证明了方法的有效性和准确性. 关键词： 半空间物理光学方法 半空间并矢格林函数 图形电磁学 雷达散射截面     

半空间背景下目标电磁散射等效模型研究

在电磁场积分方程方法框架下,应用等效原理求解了半空间背景下目标的电磁散射问题,可针对目标仅处于半空间界面单侧及目标跨越半空间界面处于半空间两侧的几何相对位置。与传统的半空间格林函数计算方法不同的是,这一方法使用的是各自介质的自由空间格林函数,因此可以回避索墨菲积分并且可以很方便与快速算法(如多层快速多级子)相结合,并对求解临近半空间界面的目标获得较好的收敛性。在等效原理方法中需要用有限的界面等效无限大半空间界面,因此采用了锥形入射波以降低开放边界引起的边缘效应。不同于一般目标的远场雷达散射截面表达,在该模型下,半空间电磁散射的远场描述需要用差场雷达散射截面。给出的算例能与现有文献以及仿真软件很好的吻合,并可作为实用工具分析半空间背景对目标远场响应的影响。     

Analysis of one-dimensional rough surface scattering based on bidirectional reflectance distribution function model

Through in-depth analysis of the scattering properties of a one-dimensional random rough surface, a method to calculate the spatial bidirectional reflectance distribution function (BRDF) characteristics of a randomly rough surface is proposed. The scattering characteristics of an electrically large rough surface can be substituted by combination of subsection electromagnetic fields. The radar cross-section (RCS), which is transformed from the BRDF, is compared with numerical results from the Method of Moment (MoM). The agreement of the results verifies that this method could calculate the electromagnetic scattering field efficiently and straightforwardly. Moreover, the resulting combined fields from the BRDF of subsections in the rough surface show a good match with the entire scattering field of a whole surface, which indicates that a large electrically rough surface could be feasibly and effectively substituted with the combination of scattering elements using the BRDF method and the statistical method.     

多层球对高斯波束散射的德拜级数研究

基于广义洛伦兹-米氏理论,利用多层球粒子散射系数的德拜级数展开公式,提出了一种新的研究多层球粒子对高斯波束散射的方法。计算结果与已有的广义洛伦兹-米氏理论算法的计算结果吻合得很好。利用该方法有效分离了折射率分布满足指数变化规律的多层球粒子对高斯波束散射的远区散射场中多阶彩虹的干涉强度分布。数值模拟了双层球的归一化双一阶彩虹强度分布以及各层的一阶彩虹艾里结构。最后分析讨论了高斯波束的入射位置和束腰半径对多层球单阶彩虹强度分布的影响。     

The influence of the characteristics of a collection of particles on the scattered spectral density and its applications

The far-zone scattered spectral density of a light wave on the scattering from a collection of particles is investigated, and the relationship between the character of the collection and the distribution of the scattered spectral density is discussed. It is shown that both the number of particles and their locations in the collection play roles in the distribution of the far-zone scattered spectral density. This phenomenon may provide a potential method to reconstruct the structure character of a collection of particles from measurements of the far-zone scattered spectral density.     

Time-Domain Scattering Modelling of Two-Dimensional Cylinder Located on a Rough Surface

Numerical modelling on the transient electromagnetic scattering by a two-dimensional （21）） cylinder located on a time-evolving rough surface is presented by using time-domain integral equations. The proposed special choice of a tapered Gauss pulse incident wave removes the truncation error from the rough surface. Additionally, a two-level averaging technique is utilized to overcome the instability from the time marching procedure of solving integral equations. Excellent correspondences between the surface current distributions, as well as the far-zone fields, computed by the proposed method and that obtained by the traditional method of moments associated with the inverse discrete Fourier transformation scheme demonstrate the accuracy of the modelling.     

Condition for far-zone spectral isotropy of an electromagnetic light wave on weak scattering

The far-zone spectral isotropy of an electromagnetic light wave on scattering has been discussed. It is shown that a sufficient condition for the far-zone spectral isotropy of an electromagnetic light wave on scattering can be expressed by the following two requirements: the two-point correlation function of the dielectric susceptibility of the scattering medium obeys the so-called scaling law, and the normalized spectrum of the incident light wave has the same distribution along the two perpendicular directions.     

Stokes parameters of an electromagnetic light wave on scattering

Stokes parameters of an electromagnetic light wave on scattering have been discussed, which permit us to study the spectral degree of polarization of the far-zone scattered field. An example of scattering of a spatially coherent electromagnetic light wave from a quasi-homogeneous medium has been discussed to illustrate the changes of the Stokes parameters and the changes of the spectral degree of polarization of the far-zone scattered field.     

天线-罩系统的散射计算

应用物理光学法(PO)对天线-罩系统的散射特性进行分析。通过对罩壁的局部平板等效,导出了天线表面的感应电流和罩表面的等效电、磁流分布的计算公式。以口径天线-多层介质结构雷达罩为例,计算了天线、雷达罩及天线-罩系统的单、双站雷达散射截面(RCS),并研究了当照射波频率和天线扫描角变化时RCS的变化规律。     

Theory of waveguide light scattering in an integrated optical waveguide in the presence of noise

We develop a vector theory of waveguide monochromatic light scattering in an integrated optical waveguide with arbitrary three-dimensional irregularities in the presence of noise. The electrodynamical problem of laser radiation scattering in an irregular waveguide is solved by the method of coupled modes with the help of the theory of perturbations. The approximate solution of the inhomogeneous three-dimensional wave equation is derived by the method of modes and the method of Greens functions. The obtained Greens function is analyzed for the cases of propagating and evanescent modes of an irregular asymmetric optical waveguide. Analytical formulas for the near- and far-zone radiation fields are presented. A preliminary analysis of these formulas is given.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 48, No. 1, pp. 63–75, January 2005.     

On the use of the multifrequency method for studying scattered fields during the antenna measurements in an anechoic chamber

We consider a method of far-zone wideband antenna measurements performed at discrete frequencies with subsequent synthesis of the tested-antenna response in the time domain for separating the useful signal and interference due to scattering. Experimental results of a study of the scattered fields arising during the measurements of characteristics of centimeter-wave horn antennas on a standard facility in an anechoic chamber are presented.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 47, No. 12, pp. 1066–1077, December, 2004.     

膨胀石墨 3 mm波消光数值计算

为探讨膨胀石墨作为3 mm波干扰材料的消光、散射特性及其影响因素, 基于有限长度、有限电导率圆柱状导体的电磁散射, 利用矩量法建立了膨胀石墨的消光、散射、吸收及后向散射截面(雷达散射截面RCS)的计算式. 运用Mathematica编程计算并分析了膨胀石墨长度、半径、电导率、磁导率等因素与膨胀石墨消光、散射、吸收截面及RCS的关系. 结果表明: 当膨胀石墨的长度为1.5 mm、半径为0.05 mm时, 具有较好的消光、散射效果; 适当增大膨胀石墨的电导率、磁导率, 有利于提高其消光、散射能力. 本研究为探索增强膨胀石墨干扰3 mm波效果的技术途径提供了有价值的参考. 关键词： 膨胀石墨 石墨层间化合物 消光截面 矩量法