MoM/PO混合法中劈绕射电流基函数研究

论文给出了Bilow所提出的绕射电流基函数的理论依据,并把这种电流基函数和Burnside所提出的绕射电流基函数作了比较.考虑到绕射理论和基本电磁理论场量关系,对Bilow绕射电流基函数在过渡区和非过渡区分别进行了修正,提出了新的绕射电流基函数.三种基函数模拟的结果和理想导体劈绕射的解析解进行了比较,证明目前所采用的基函数精度最高.     

复杂散射环境中MoM与UTD混合方法的PO扩展

本文提出利用物理光学PO可扩展MoM UTD的应用范围 .理论和数值结果表明 ,PO电流的引入抛开了MoM UTD混合中的镜像原则 ,使散射体扩展到任意复杂面 ,以及很好地解决了线天线距离弯曲曲面较近的情况下UTD技术的缺陷 .另外 ,本文指出适当比例的PO区域仍可以较准确地求解MoM区域的电流和阻抗特性 ,使得本文方法变得简单有效 ;这为快速有效地分析复杂电大目标的电磁兼容问题提出了一条新的切实可行的途径     

Spaceborne Mesh Reflector Antennas With Complex Weaves: Extended PO/Periodic-MoM Analysis

Reflector antennas with complex mesh weave patterns are numerically analyzed by using extended physical optics (PO) combined with the periodic method of moments (MoM). The method applies the periodic MoM with Rao-Wilton-Glisson (RWG) basis and testing functions. It calculates the transmission coefficient matrix (T-matrix) of the realistic, complex weave pattern of the planar mesh, in order to calculate the modified PO current on the mesh reflector. When analyzed, the planar grid mesh is found to be compatible with the commonly used wire-grid model. The modified PO current on the locally planar mesh is implemented on the curved reflector surface for the diffraction analysis of the mesh reflector antennas. The far-field pattern of the offset parabolic antenna with grid mesh, modelled using periodic MoM, agreed well with those obtained from the wire-grid model. T-matrix calculated from the tabulated T-matrix data using the interpolation method is sufficiently accurate and compares well with the one calculated using the direct method, allowing users to choose one of the T-matrix calculation methods depending on the problem. The analysis of the mesh reflectors with two different complex weave patterns (single Satin and single Atlas at Ka band) is performed to exemplify the application of the extended PO/periodic MoM algorithm. It is shown that differences were observed in cross-polarization discrimination (XPD) for circular polarization operations depending on the weave patterns. This result demonstrates the usefulness of the proposed technique in accurate performance prediction of mesh reflector antennas with complex weave patterns     

二维组合目标RCS的MoM-PO混合法分析

利用矩量法求解二维目标结构的电磁散射问题,并在电流基混合法的基础上,对矩量法和物理光学混合法进行了研究,推导出了一种矩阵方程表达式,并通过仿真实例分析了以物理光学混合法计算多组合复杂目标散射时,物理光学区域与矩量法区域的划分方式,仿真结果证明,此区域划分结论的准确性、可行性。     

An Improved UTD Based Model for the Multiple Building Diffraction of Plane Waves in Urban Environments by Using Higher Order Diffraction Coefficients

This paper describes an improved model for multiple building diffraction modeling based on the uniform theory of diffraction. A well-known problem in conventional uniform theory of diffraction (CUTD) is multiple edge transition zone diffraction. Here, higher order diffracted fields are used in order to improve the result. Hence, we use higher order diffraction coefficients to improve a hybrid physical optics (PO)-CUTD model, the results show that the new model can correct errors of the PO-CUTD model. Therefore, the proposed model can find application in the development of theoretical models to predict more realistic path loss in urban environments, when multiple building diffraction is considered.     

Analyzing electromagnetic pulse coupling by combining TLT, MoM, andGTD/UTD

An important problem in electromagnetic compatibility (EMC) analysis is to determine the coupling of an electromagnetic field into a shielded cable. Using the transmission line theory (TLT), the disturbance voltage induced inside the cable is easily calculated from the current distribution on its shield. This current distribution depends on the incident electromagnetic field and is efficiently determined by the method of moments (MoM). Extending the MoM with the geometrical and uniform theory of diffraction (GTD/UTD) makes it possible to solve scattering problems that are too large and too complex for the plain MoM. The combination of the three approaches-TLT, MoM, and GTD/UTD-allows calculation of the disturbance voltage inside a shielded cable, which is part of a complex scattering structure. The fundamentals of each method and the way of putting them together are shown in this paper. The application of the proposed method is demonstrated by an example: the pulse coupling between a monopole antenna and a shielded cable is analyzed, taking into account a large conducting structure in the vicinity     

Improved PO-MM hybrid formulation for scattering fromthree-dimensional perfectly conducting bodies of arbitrary shape

The method of moments (MM) represents a suitable procedure for dealing with electromagnetic scattering problems of arbitrary geometrical shape in the lower frequency range. However, with increasing frequency both computation time and memory requirement often exceed available computer capacities. Therefore a current based hybrid method combining the MM with the physical optics (PO) approximation suitable for three-dimensional perfectly conducting bodies is proposed in this paper. The hybrid formulation allows a substantial reduction of computation time and memory requirement, while the results are in reasonable agreement with those based on an application of the MM alone. Further improvement can be achieved for flat polygonal parts of the scattering body by a heuristic modification of the PO current density taking into account the effects of edges. As opposed to the physical theory of diffraction (PTD), no additional electric and magnetic line currents along the edges are necessary     

Extensions to the hybrid method of moments/uniform GTD formulationfor sources located close to a smooth convex surface

We present an extension to the uniform geometrical theory of diffraction (GTD) for reflection from smooth curved surfaces. This approach allows the source to be much closer to the reflecting surface than the conventional uniform GTD formulation and does not require a Hertzian dipole source. In essence, the field point is mirrored in the plane tangential to the specular (reflection) point; the incident field is then calculated at the mirror point and the uniform GTD reflection coefficients are used to mirror this field to the original field point. This formulation reduces exactly to the conventional uniform GTD if the incident field is ray optical. The application to a hybrid method of moments (MoM)/GTD code is outlined and results computed using this code are presented for a dipole radiating in the vicinity of a cylinder     

矩量法-物理光学混合算法计算多尺度复合目标电磁散射场

基于电流的矩量法（method of moments，MoM）和物理光学法（physical optics，PO）的混合算法是目前求解电中尺度和多尺度目标电磁散射和辐射的主要方法，在计算MoM区和PO区的耦合作用时需要对PO区域进行亮区判断.传统纯CPU亮区判断方法时间复杂度为O（N2），时间消耗随着面片数量N增加而急剧增大.文中通过GPU渲染功能及对深度缓冲区（zbuffer）的利用，对PO亮区判断过程进行加速，亮区消耗时间与面片数量无直接联系，在面片数量达到105数量级以上加速优势明显.将加速的MoM-PO混合方法应用于复杂目标与粗糙面的组合情况，对比多层快速多级子（multi level fastmultipole method，MLFMA）方法，相比于纯PO方法，获得较高的精度.相比于单一算法，混合算法有明显优势.     

Analysis of Antenna Around NURBS Surface With Hybrid MoM-PO Technique

The hybrid method of moments and physical-optics (MoM-PO) approach is used to calculate the radiation pattern of antenna around arbitrarily shaped structure. The structure is modeled with Non-uniform rational B-spline (NURBS) surfaces. The hybrid MoM-PO approach is implemented by modifying the impedance matrix of the MoM region with PO. Formula for the scattered PO field is deduced for cases of antenna located around NURBS surface. The stationary phase method (SPM) is applied for the integral of the induced current in the PO region. Results obtained from this method and from MoM-PO approach based on triangle facet model agree well while the former is more efficient in execution time     

Higher order hybrid method of moments-physical optics modeling technique for radiation and scattering from large perfectly conducting surfaces

An efficient and accurate higher order, large-domain hybrid computational technique based on the method of moments (MoM) and physical optics (PO) is proposed for analysis of large antennas and scatterers composed of perfectly conducting surfaces of arbitrary shapes. The technique utilizes large generalized curvilinear quadrilaterals of arbitrary geometrical orders in both the MoM and PO regions. It employs higher order divergence-conforming hierarchical polynomial basis functions in the context of the Galerkin method in the MoM region and higher order divergence-conforming interpolatory Chebyshev-type polynomial basis functions in conjunction with a point-matching method in the PO region. The results obtained by the higher order MoM-PO are validated against the results of the full MoM analysis in three characteristic realistic examples. The truly higher order and large-domain nature of the technique in both MoM and PO regions enables a very substantial reduction in the number of unknowns and increase in accuracy and efficiency when compared to the low-order, small-domain MoM-PO solutions. The PO part of the proposed technique, on the other hand, allows for a dramatic reduction in the computation time and memory with respect to the pure MoM higher order technique, which greatly extends the practicality of the higher order MoM with a smooth transition between low- and high-frequency applications.     

阻抗劈散射的MM-PO混合算法研究

本文系统地研究了各向异性阻抗劈绕射的矩量法-物理光学(MM-PO)混合算法.首先研究了任意各向异性阻抗面的物理光学模型,推导出表面物理光学等效电磁流计算式.其次,提出了一种有效的含Hankel函数的弱振荡被积函数无穷积分处理方法.最后,将作者已公开发表的修正绕射电流基函数用于各向异性阻抗劈散射场研究,数值结果和已知的一致性绕射理论结果高度吻合.     

利用UTD修正的MoM-PO混合算法研究

介绍了利用矩量法(MoM)和物理光学(PO)混合方法处理复杂线体结构的电磁散射问题，提出利用pulse基函数对线电流进行展开，使得处理复杂线体结构问题变得简化，并推导出一般的矩阵方程。然后针对PO在阴影区域失效等问题，利用UTD(一致性几何绕射)对该简化模型结构下的PO区域电流进行了修正，使得其应用范围得到扩展、计算精度得到提高。文中的实例结果与传统的MoM很好的一致，从而说明了该方法的有效性和精确性。     

MoM-NPO混合算法分析天线-载体系统

安装在电大尺寸平台上的天线,载体的影响不容忽视。采用同样基于电流展开的矩量物理光学混合算法,并通过NURBS物理光学法进一步降低复杂结构的建模和计算,将载体对天线的影响用物理光学电流合并到包括天线的在内较小的矩量法区,使矩量法解决天线-载体系统成为可能。通过矩量法和混合算法分析载体对天线性能的影响证明,载体对天线的影响是显著的,混合算法能够在保证精度的前提下提高运算速度,为解决电大尺寸载体上天线的特性提供了良好的途径。     

机载天线辐射方向图的MoM-UTD混合法分析

采用矩量法(MoM)结合一致性几何绕射理论(UTD)的混合方法分析了机载单极天线的辐射特性。用该混合方法建立的机载天线辐射模型更符合实际,并且它同时具有MoM的精确性和UTD的高效性,克服了单一方法的不足。计算结果对于预测天线间的电磁兼容性和优化天线布局具有一定的指导意义。     

Diffraction by an anisotropic dielectric half-plane: a uniformasymptotic PO solution

A uniform solution is proposed to, describe the diffraction by a penetrable anisotropic dielectric halfplane illuminated at normal incidence by an electromagnetic plane wave. Resorting to second-order boundary conditions on a sheet simulating a special type of anisotropic dielectric thin layer, a physical optics (PO) approximation for the induced electric and magnetic surface currents is derived. Then, a uniform asymptotic evaluation of the corresponding radiation integral provides the diffracted field in terms of the standard transition function relevant to the uniform theory of diffraction. The effectiveness of the solution is proved by many numerical tests     

Plane-wave diffraction by a wedge--A spectral domain approach

The canonical problem of plane wave diffraction by a wedge in the context of the spectral domain approach which exploits the relationship between the induced current on a scatterer and its far field is investigated. It is shown how the exact solution to the wedge diffraction problem can be manipulated in a form which enables one to interpret the far scattered field as the Fourier transform of the physical optics (PO) current on the two faces of the wedge augmented by the fringe current near the tip of the wedge. A uniform asymptotic expansion for the total field which slightly modifies the Ansatz in the uniform asymptotic theory of electromagnetic edge diffraction is constructed.     

理想导体半圆柱TE波散射的混合法解

本文应用混合技术分析了在TE平面波激励下,理想导体半圆柱的双站散射。该混合技术是把半圆柱劈附近的电流表示为未知数,圆柱曲面上的一阶电流应用Fock理论求解,高阶绕射电流表示为含有未知系数的Fock型函数。圆柱平面上的一阶电流用物理光学近似和曲劈的一致性几何绕射理论得到。劈的二阶绕射电流表示为含有未知系数的GTD形式。然后通过磁场积分方程,运用简单矩量法求得劈附近的电流和未知的绕射系数。最后计算了理想导体半圆柱的双站散射截面,结果与矩量法的结果吻合得相当好。     

Ray tracing with PO/PTD for RCS modeling of large complex objects

The present paper deals with a new efficient approach in order to assess the simulation of scattered fields from arbitrary metallic objects. The basic idea is to combine a ray tracing algorithm with the principles of physical optics (PO) and the physical theory of diffraction (PTD). The ray tracing algorithm stochastically launches discrete rays and uses a ray density normalization. In order to perform simulations at finite objects the PO/PTD formulation is required. Thus, fast intersection routines can be implemented, while the ray density formulation reduces the PO and PTD integrals to a pure sum of ray contributions. Simulation results obtained with this model are verified by comparison with both exact simulations using a method of moments (MoM) code and measurement results, proving an excellent accuracy and fast computation even at complex objects. With this asymptotic approach, scattering properties of large objects that are too complex for exact methods can be analyzed with rather moderate computation efforts. Typical applications include the simulation of low observability (LO) designs as well as the generation of databases for identifying unknown aircraft by their radar signature.     

高阶MoM及其与PO的混合法计算电磁散射问题

本文提出了一种新的以高阶矩量法(MoM)与物理光学法相结合的混合法(MoM-PO).该方法采用曲面参数化的离散方法,保证了建模的精确性.计算过程中将散射表面灵活划分为MoM区和PO区,在各自区域可以灵活确定离散单元的大小和密度.MoM区域的高阶矩量法,采用基于Lagrange插值的高阶矢量基函数,结合点匹配技术,比传统的高阶法简单,易于实现.计算结果表明,本文的高阶矩量法及其与物理光学法结合的混合方法能准确有效的计算目标的电磁散射特性.