扩大瞬时散射场FDTD计算区域的新方法

本文采用非均匀网格来扩大瞬变电磁场ＦＤＴＤ法计算区域，可在不增加甚至减少存贮量和计算量的情况下，有利于空间时间窗的应用，减小或避免截断边界对计算结果的影响，提高其精度和可靠。本文以圆柱目标为例，讨论分析了采用吸收边界条件和本方法所得结果的可靠性。     

二维散射问题的一个完整的时域解

本文研究了利用卷积直接求解瞬态散射远场的方法，得到二维散射问题完整的时域解，通过计算实例与严格理论解的比较，表明算法的正确性，评议中给出几种规则散射体的RCS和瞬态散射远场的计算结果。     

用复射线展开法计算目标散射场的误差特性分析

复射线展开法是计算目标散射场的一种简捷的方法，其可靠性有赖于对误差特性的系统研究，本文以平面波谱积分为散射计算的参考标准，以Ｌ＾２空间中由范数定义的距离作为复射线展开法计算结果的误差，从而得到了复射展开法在目标散射场计算中的误差特性，找到了减误差的方法并给出这一方法的适应范围。     

改进的FDTD法分析研究无限长导体柱上棱边TM散射之间的相互影响

本文用改进的ＦＤＴＤ法（时域有限差分法）分析研究了带有棱边的无限长导体柱ＴＭ散射问题，以长方形导体柱为例，对棱边附近ＴＭ散射电流之间的相互影响进行了计算，数值计算结果表明棱边散射电流之间的相互影响比较明显，在近场问题中应特别予以考虑。在导体桂边附近的网格点上将近似场解直接引入差分方程，对ＦＤＴＤ方法进行了改进。同时本文对棱边周围的近场进行了分析计算，得出了棱边用导电劈近似处理的一些相关条件。     

新型箔片云团双站电磁散射计算方法研究

提出了计算圆形、四边形金属箔片云团单箔片双站ＲＣＳ的方法，给出了极化变换和散射矩阵计算的具体公式，可用于大数量高密度箔片云团双站ＲＣＳ计算研究，并给出了数值结果。     

复宗量菲涅耳积分的计算及其性质

复宗量菲涅耳（Ｆｒｅｓｎｅｌ）积分的计算，是有耗介质劈电磁散射中遇到的一个难题。本文综合运用了复宗量菲涅耳积分的小宗量级数展开和大宗量渐近展开，并且找到了大宗量展开与小宗量展开的衔接部，圆满地解决了菲涅耳积分在整个复平面内的计算机计算问题。本方法计算速度快，精度高。此外，本文还研究了菲涅耳积分在复平面上的对称性、零点等性质，给出了菲涅耳积分在复平面上的三维立体图和二维等值线图。     

求解目标地波散射特性的方法研究

本文把求解半空间散射问题的FDTD技术与地波传播理论相结合，研究任意复杂目标的地波散特性。入射地波设置在FDTD计算区域中的总场边界上并在散射场输出边界面上提取散射近场数据，然后利用等效及镜像原理，计算无地波衰减时的远区散射场，通过引入地波衰减因子，把该远区散射场转换为远区地波散射场，文中给出了方法验证例子以及一个较复杂目标的单站RCS计算结果。     

N阶色散媒质的瞬态散射特性

本文提出了Ｎ阶色散媒质瞬态特性的时域分析方法，结合Ｚ变换对常规的时域有限差分（ＦＤＴＤ）法进行了修正，改进后的ＦＤＴＤ法能分析和与频率有关的电磁场问题，具有方法简洁、易实现等优点。为验证此方法的有效性和可靠性，对Ｎ阶色散媒质的反向系数进行了分析与计算，并与已知的解析结果进行了比较，同时，采用此时域方法对Ｎ阶色散媒质和导体覆盖Ｎ阶色散媒质散射场进行了计算和分析。     

混合法在二维导体目标散射中的应用

本文介绍了以高频渐近法和矩量法为基础的一种求解复杂散射体的混合法，并结合计算实例分析了该方法的特点，准确性以及目前存在的缺点。     

阻抗劈中的等效边缘电磁流

本文把应用于理想导体劈中的等效边缘电磁流概念推广应用到阻抗劈上，导出了劈边缘在产面波斜入射情况下与阻抗劈绕射密切相关的等效边缘电磁流表达式，然后利用辐射积分公式，给出了有限长直劈的电磁散射解。为计算平板模型机翼的ＲＣＳ打下了理论基础，文中给出的计算实例说明了本文方法的有效性。     

源在曲面上的NURBS-UTD方法的爬行波射线寻迹算法研究

辐射源位于凸曲面上的一致性几何绕射理论(UTD)在分析设计电大尺寸平台上天线的应用广泛,本文给出了一种源点位于任意光滑凸曲面上的UTD爬行波射线寻迹算法,使用数值的微分几何方法对暗区爬行波射线进行寻迹.对目标模型引入非均匀有理B样条(NURBS)曲面进行建模,这使得UTD方法可以应用于以往板、柱、锥模型以外的任意光滑曲面模型.本文算法可应用于任意曲面上,数值结果表明了本文算法的有效性及工程适用性.     

应用NURBS-UTD方法分析受扰方向图

 本文研究基于任意曲面建模的UTD方法,引入NURBS曲面建模技术对电大尺寸目标建模,给出了NURBS-UTD方法中反射射线场以及表面绕射射线场的数值求解方法。与曲面有关的具体参数,根据微分几何的基本原理结合参数曲面定义使用各种数值方法进行处理,对线积分使用定义展开。针对实际当中任意几何造型的电大尺寸平台的电磁特性分析,本文方法不仅能够处理初等解析曲面,也能够处理任意弯曲的曲面模型,并且不需要消耗大量计算资源又提高了建模精度,文中给出实例进行说明。     

NURBS-UTD方法的反射射线寻迹算法研究

针对目前的UTD方法无法处理任意弯曲模型这一缺陷,该文将CAGD中广泛使用的NURBS曲面建模技术与计算电磁学中广泛使用的UTD方法相结合,讨论了NURBS-UTD方法的反射射线寻迹算法.该算法可应用于包括UTD方法中典型的柱、锥在内的任意曲面上,数值结果表明了算法的有效性及实用性.     

Overview of MM and UTD methods at the Ohio State University [radartarget scattering]

Techniques appropriate for low and high frequency numerical evaluation of the scattered fields from complex shapes are discussed. Object size in terms of wavelengths dictates the type of solution to be used. For targets in and just above resonance, the method of moments (MM) is used. The limitation in this case is that the scatterer cannot be too large in terms of the wavelength. For radar targets in the microwave band, the uniform geometrical theory of diffraction (UTD) and modifications thereof form the basis for the computation. This has the basic limitation that the scattering mechanisms need to be known and included in the model. Examples are given for both frequency regimes     

有限元法与UTD结合计算机载天线方向图

为了计算机载天线的方向图,近区矢量场可以作为有限元法(FEM)与UTD(一致性几何绕射理论)的结合点,将二者结合以解决类似的工程问题.首先利用基于有限元法的软件HFSS计算相控阵天线的近区矢量场,然后将此结果作为UTD方法的源进一步计算以预测该相控阵天线的受扰特性.结果表明这种方法可有效用于分析机载相控阵天线的辐射特性.     

A hybrid method for computing the scattered fields from complexstructures

A new hybrid method that removes typical discontinuities and singularities of UTD solutions is described and applied to scattering by complex structures. The scattered fields from the structure are first computed on a surface S enclosing it. Then these fields are used to compute an equivalent set of electric and magnetic currents, which are then used to find the scattered fields from the structure. This method can extend the ability of available UTD computer codes to solve for the scattered fields from structures that need special treatment and are nor solvable through direct UTD means. Good agreement is shown between this new hybrid method and moment method results as well as measurements     

An engineering approach for site shielding calculations

In this paper, two models to approximately calculate the field distribution in the vicinity of a perfectly conducting finite width screen are discussed. The first model is based on the geometrical theory of diffraction (GTD), and is simplified such that the magnitude of the individual ray contributions can be easily calculated. The second model is based on a graphical approach. Coefficients that are representative for the dimensions of the obstacle and the relative position of the observation point are used together with standardized equations to calculate the field strength in the shadow region behind the screen. Also a modification of the current CCIR procedure for knife-edge diffraction is proposed, such that it can be applied to a finite width screen. Results of all models are compared with more accurate and complex results from a model based on the uniform theory of diffraction (UTD). All models proposed are simple to apply and present an essential extension to currently available engineering models. It is found that the GTD model has the best performance with respect to the UTD approach. The graphical method, however, is more user friendly than the GTD model, because fewer intermediate results need to be calculated. Moreover, the use of this method yields a field-strength distribution for the whole shadow region of the obstacle instead of the field at just a single point. Further, it is found that the modified CCIR approach can also be used with good accuracy. The models discussed answer some questions formulated by the CCIR concerning site shielding, and extend the currently available engineering models for this interference reduction technique.     

Fully Coupled Hybrid FEM-UTD Method Using NURBS for the Analysis of Radiation Problems

A novel hybrid finite element method (FEM) -uniform theory of diffraction (UTD) method for the analysis of radiating structures in the presence of electrically large objects is presented. The hybridization is done in a fully coupled way taking into account mutual interactions between the FEM and UTD regions. The UTD objects are modeled using non-uniform rational B-spline (NURBS) surfaces. Ray acceleration techniques and simple clustering strategies are used to speed up the computation time. Numerical results are presented showing the validity of the method.     

Electromagnetic scattering from appendages on a smooth surface

A solution is obtained for the high frequency backscattered far field from appendages such as an inlet mounted on arbitrary smooth surfaces. The goal here is twofold; first, to demonstrate the effectiveness of the uniform geometrical theory of diffraction (UTD) in computing the scattered fields from such complex targets, and second, to develop iterative techniques to find multiply diffracted ray paths to be used in the application of UTD. These techniques are applicable to numerically as well as analytically defined surfaces.