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.     

光滑曲面上测地线射线寻迹算法及爬行波计算

提出了一种光滑凸曲面上的一致性几何绕射理论(UTD)爬行波射线寻迹算法,该算法结合泰勒级数,并根据测地线的相关性质,使用计算几何方法对暗区爬行波射线进行寻迹;在参数曲面片上根据测地线性质求解爬行波轨迹点,并对爬行波在任意一点处的测地曲率进行计算,结果准确度高。最后使用该算法结合UTD方法计算二维圆柱的散射场,得到的结果与级数解吻合,验证了本文算法的有效性,扩展了UTD方法在实际工程中的应用。     

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.     

射线跟踪技术分析电大尺寸天线罩的寻迹算法

用几何光学——单一平面波射线跟踪技术解决电大尺寸多层介质罩内电磁波传播问题的关键任务是求解射线与各介质分界面的交点，尤其是为了考虑介质分界面曲率的影响，需要计算波阵面的曲率矩阵，因此有必要用更严格的方法来求射线与曲面的交点。论述了在已知天线罩各介质分界面曲面方程的情况下如何用数值方法中的二分法来计算射线和介质分界面的交点，其算法直观、可靠，适用的曲面方程形式广泛。     

GTD应用中任意凸曲面表面爬行波射线寻迹

射线寻迹是几何绕射理论(GTD)解决高频电磁散射和辐射问题的关键步骤.本文通过引入动态规划的数学优化方法,得到了任意凸曲面表面绕射射线的一般寻迹规划模型.并对无限长圆柱、旋转抛物面和任意构造的一凸曲面上爬行射线进行了寻迹计算,结果表明模型方法是正确的.该方法还可以应用到非均匀媒质任意凸曲面的爬行射线寻迹.     

一种求解电大平台天线互耦的时域积分方程快速算法

该文针对电大尺寸平台天线互耦问题,提出一种基于几何绕射理论加速的时域积分方程快速算法。在求解时域积分方程的经典时间步进法基础上,引入几何绕射理论中的绕射线寻迹,提高了迟滞积分的计算效率。数值算例证明了该方法能够有效地加速时间步进法的求解过程,对电大平台天线布局优化设计具有理论指导意义。     

基于NURBS建模技术的迭代MoM-PO方法分析电大尺寸平台天线方向图

本文采用基于非均匀有理B样条(NURBS,Non-Uniform Rational Bezier Spline)曲面建模技术的物理光学方法结合矩量法(Method of Moments-Physical Optics)分析位于电大尺寸平台附近天线的辐射方向图.文章推导了基于有理贝齐尔曲面的物理光学散射场计算公式.采用驻相法计算有理贝齐尔曲面上的物理光学感应电流积分.利用物理光学散射场迭代矩量法区域的电压矩阵.通过与传统平面片建模的物理光学方法的计算结果对比,说明本文方法的有效性和优点.     

基于裁剪造型的等几何分析方法求解波导本征值问题

等几何分析方法使得几何模型和分析模型能够用NURBS统一表达,避免了模型转换过程,但由于其分析域是由张量积面片构成,很难处理截面形式复杂的多联通域问题。裁剪造型等几何分析方法通过背景曲面和裁剪曲线将复杂带孔结构作为一个被NURBS曲线裁剪后的参数区域直接映射而成,只需要一个参数空间就可以表示任意复杂的拓扑结构,该方法既保留了传统等几何分析方法的优点,又实现了对复杂多孔结构的处理。本文将裁剪造型的等几何分析方法扩展到TE波的波导本征值问题,对复杂多孔结构的截止波数进行有效求解,并通过相应的数值算例验证方法的有效性和高精度性。     

组合导体目标电磁特性的快速多极算法计算

用快速多极算法分析具有任意线、面、体组合的电大尺寸理想导体目标的电磁散射和辐射特性.统一采用RWG基函数对线、面、体导体上的电流进行展开;使用了新的设置基函数和未知量的方法来处理任意的线-面,面-面连接问题;并使用多层快速多极算法结合ILUT预处理算法加速求解过程.数值结果验证了本文方法的准确性和高效性.     

一种基于几何统计的卫星移动MIMO信道模型

结合统计模型复杂度低和几何模型精确度高的优点,提出了一种基于几何统计的双极化卫星移动多输入多输出(MIMO)系统的信道建模理论。该模型总体上使用几何模型的建模思路,采用射线追踪方法对信道中传输的射线进行追踪,重点关注各条射线的各种小尺度参数,在实际计算中引入统计学方法对各种小尺度参数进行建模与处理,同时考虑信道环境造成的信号衰减以及信道环境对射线极化的影响,完成了信道模型的建立。根据已完成的建模理论,利用Matlab实现极化卫星移动MIMO信道的建模与仿真。通过与增强型统计模型仿真结果进行比较,得出了此几何统计模型是正确的,并可在一定程度上提高建模准确性的结论。     

Combining the moment method with geometrical modelling by NURBSsurfaces and Bezier patches

Induced current distributions on conducting bodies of arbitrary shape modelled by NURBS (non uniform rational B-splines) surfaces are obtained by using a moment method approach to solve an electric field integral equation (EFIE). The NURBS surfaces are expanded in terms of Bezier patches by applying the Cox-de Boor transformation algorithm. This transformation is justified because Bezier patches are numerically more stable than NURBS surfaces. New basis functions have been developed which extend over pairs of Bezier patches. These basis functions can be considered as a generalization of “rooftop” functions. The method is applied to obtain RCS values of several objects modelled with NURBS surfaces. Good agreement with results from other methods is observed. The method is efficient and versatile because it uses geometrical modelling tools that are quite powerful     

考虑多次散射的复杂目标一体化电磁散射计算

在复杂目标电磁散射计算中,表面散射、棱边散射以及凹形结构的多次散射是最为重要的几种散射贡献。研 究了包含表面散射、棱边散射和凹形结构多次散射的复杂目标一体化电磁散射计算方法,开发了基于UG 建模软件的 一体化电磁散射计算软件,其中表面散射计算采用了图形电磁计算方法,棱边散射算法采用ILDC,并使用UG/Open 实现了复杂目标棱边自动识别,对于包含多次散射的腔体等凹形结构,开发了基于NURBS 曲面的射线追踪方法和SBR 算法,实现了腔体结构多次散射计算。所有算法都统一在UG 建模软件中开发,实现了从目标几何建模到散射计算的 一体化,简化了模型前处理过程。算例表明,所开发的一体化散射计算软件计算精度高,通用性强,具有很好的工程 应用价值。     

Analysis of antennas on board arbitrary structures modeled by NURBSsurfaces

An accurate and efficient numerical scheme has been developed for predicting high-frequency radiation patterns of antennas mounted on arbitrary structures modeled by parametric surfaces. The method is based on geometric optics (GO) and the uniform theory of diffraction (UTD). Nonuniform rational B-splines (NURBS) surfaces have been used to describe the geometry of the structure. As most of the computer-aided geometric design (CAGD) tools available in the industry are biased on NURBS, the scheme can perform the electromagnetic analysis without any new or additional remeshing of the geometrical model. A special ray-tracing technique that combines GO and UTD with NURBS has been developed. This technique uses some selective criteria in order to identify rapidly the NURBS where a ray impact may occur. Impact point coordinates are obtained by means of an optimization procedure based on the conjugate gradient method (CGM). The accuracy and efficiency of the approach are shown comparing it with other methods     

任意形状电大散射体附近天线受扰方向图的快速分析

该文采用基于非均匀有理B样条曲面(NURBS)建模的物理光学方法结合矩量法(MoM-PO)分析任意形状电大散射体附近天线的受扰方向图。采用插值驻相点技术加快了方向图的计算速度。文章推导了基于有理贝齐尔曲面的物理光学散射场计算公式,采用驻相法(SPM)计算有理贝齐尔曲面上的物理光学感应电流积分从而得到物理光学散射场,并利用物理光学散射场迭代矩量法区域的电压矩阵。通过与传统平面片建模的物理光学方法的计算结果对比,说明该文方法的有效性和计算速度快的优点。     

Application of physical optics to the RCS computation of bodiesmodeled with NURBS surfaces

The paper presents a method for the computation of the monostatic radar cross section (RCS) of electrically large conducting objects modeled by nonuniform rational B-spline (NURBS) surfaces using the physical optic (PO) technique. The NURBS surfaces are expanded in terms of rational Bezier patches by applying the Cox-De Boor transform algorithm. This transformation is justified because Bezier patches are numerically more stable than NURBS surfaces. The PO integral is evaluated over the parametric space of the Bezier surfaces using asymptotic integration. The scattering field contribution of each Bezier patch is expressed in terms of its geometric parameters. Excellent agreement with PO predictions is obtained. The method is quite efficient because it makes use of a small number of patches to model complex bodies, so it requires very little memory and computing time     

Surface ray analysis of mutually coupled arrays on variable curvature cylindrical surfaces

Two previously developed ray methods for conformal arrays on surfaces with variable curvature are further systematized and applied to arrays of equispaced identical slits on perfectly conducting parabolic cylindrical surfaces. The two methods differ in their definition of the canonical problems that are fundamental to the scattering process. In the first method, multiple scattering on the smooth cylinder surface accounts for interaction between isolated elements, while in the second, surface rays are defined on a local periodically loaded surface. The first method is valid under quite general conditions and yields reliable numerical results for mutual-coupling coefficients and radiation patterns. The second provides a simple explanation of a variety of coupling and radiation phenomena when the array possesses aspects of periodicity, and it is preferable for numerical calculation of mutual coupling in large arrays. These features are illustrated in detail on a particular example. The results obtained confirm the utility of the ray analysis in furnishing solutions for coupling coefficients and element patterns in conformal arrays, and they also demonstrate the fundamental insight gained by the local periodic-structure approach.