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.     

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.     

缝隙天线阵双站电磁散射的混合法

利用矩量法（ＭＯＭ）和等效边缘电磁流方法（ＥＥＣｓ）研究波导馈电的缝隙天线阵的双站散射问题。从理论和计算上分析,等效边缘电磁流方法可以计算有限尺寸的导体平板沿任意方向上的双站散射（包括边缘绕射场）,而矩量法可以考虑波导缝隙天线阵的散射与耦合问题,使它们混合便可以解决有限尺寸缝隙在线阵的散射问题。实际计算表明,方法是切实可行的。     

MM—PO混合法中一致性劈面绕射电流研究

研究了MM-PO混合算法中的劈面绕射电流基函数.基于一致性绕射理论,导出了不分区域的统一的一致性劈面绕射电流表达式,提出了UTD修正的MM-PO混合算法.理论分析和仿真计算表明,一致性MM-PO混合算法克服了当劈面从过渡区外向过渡区逐步逼近时分区域表达式的不连续性的困难,消除了相应的模型误差.研究还表明,所得到的修正混合算法也适用于阻抗劈包括各向异性阻抗劈情形.     

涂覆型大尺寸有限长圆柱散射特性的混合解法

本文首先从理论上导出了能计算斜入射绕射场的阻抗劈并矢绕射系数,然后利用该绕射系数结合物理光学法对涂覆型大尺寸有限长圆柱的散射特性进行了分析和计算。在绕射区计及了一阶和二阶绕射贡献,在镜反射方向附近作了驻相法近似,由此得到的数值结果与实验结果吻合较好。     

单翼圆柱电磁散射的混合解

本文利用混合法分析和计算了单翼理想导电圆柱远场散射。这种混合法应用了物理光学近似（ＰＯ）、ＦＯＣＫ理论、物理绕射理论（ＰＴＤ）、几何绕射理论（ＧＴＤ）和矩量法。计算结果与矩量法和Ｍｉｃｈｅａｌｉ的计算和测量结果一致。与Ｍｉｃｈｅａｌｉ的方法相比，混合法对于任意尺寸的圆柱半径与翼宽和任意的入射角都适用。     

复杂电磁环境中线天线近场数模预测

本文应用矩量法和几何绕射理论的混合技术及矩量法的稀疏技术详细分析和计算了多导体同时存在的复杂电磁环境中线天线的近场。理论值与实验数据进行比较，两者基本吻合。     

复杂电磁环境中线天线近场数模预测

本文应用矩量法和几何绕射理论的混合技术及矩量法的稀疏技术详细分析和计算了多导体同时存在的复杂电磁环境中线天线的近场，理论值与实验数据进行比较，两者基本吻合。     

修正劈表示的边缘等效电磁流的改进及在电磁散射中的应用

本文介绍了修正劈的概念和用其表示的等效边缘电磁流（ＥＥＣ）公式，并应用它们计算了圆盘双站雷达散射截面（ＲＣＳ）；提出一种确定修正劈方向的法则，这种法则是根据几何绕射理论（ＧＴＤ）中有关参数的定义确定的，因而它不是经验的法则。修正劈表示的ＥＥＣ仅利用了经典的Ｋｅｌｌｅｒ锥上的绕射系数公式和修正劈的概念就可得到任意入射和观察方向的ＥＥＣ，它克服一般ＥＥＣ在Ｋｅｌｌｅｒ锥外的方向上定义模糊的缺点。数值结     

不同消失矩的小波在小波矩量法中的应用比较

应用具有不同消失矩的Daubechies小波对平面波照射的无限长理想导体圆柱的表面电流进行了计算,研究了小波消失矩阶数对阻抗矩阵压缩率的影响.分析表明在小波矩量法中,对于一般的二维散射问题,8阶消失矩是比较好的,低于8阶得不到很好的压缩效果,高于8阶不但不能得到更好的压所效果还会增加计算量:该结论对小波矩量法中小波消失矩的选取有一定的指导意义.     

A study of a monopole arbitrarily located on a disk using hybrid MM/GTD techniques

The input impedance of a monopole located off-axis on a disk and oriented in an arbitrary direction is investigated using hybrid method of moments/geometrical theory of diffraction (MM/GTD) techniques. The equivalent currents method (ECM) and the uniform geometrical theory of diffraction (UTD) are used to ensure a proper treatment of each situation. A criterion for switching from UTD to ECM in the vicinity of the axial caustic is discussed. Measurements of impedance have been made in order to check the numerical results and are presented here, showing good agreement with theory.     

Closed-form expressions for uniform currents on a wedge illuminatedby TM plane wave

Closed-form expressions for nonuniform currents on a perfectly conducting, infinite wedge illuminated by a transverse magnetic plane wave are presented. The expressions are derived by requiring that they agree with the current predicted by the eigenfunction solution close to the edge and J.B. Keller's geometrical theory of diffraction (1962) far from the edge. The angle of incidence is arbitrary and the expressions remain uniformly valid even for glancing angles of incidence when the geometrical optics boundaries are in the vicinity of the wedge faces. The formulas presented are simple, involving Fresnel functions with complex arguments. These functions can be expressed in terms of complimentary error functions which may be computed using standard subroutine packages. Exact expressions for nonuniform currents are available for the two special cases of half-planes and infinite planes. Closed-form expressions for the axial electric field, and hence all the field components in the vicinity of the wedge axes, are also obtained. Currents computed using expressions obtained are compared with currents computed from the eigenfunction solution of the wedge, with good agreement throughout     

用UTD-MOM混合法有效分析大型平面阵列天线的辐射特性

采用矩量法(MOM)结合一致性几何绕射理论(UTD)来分析和计算大型平面阵列天线的辐射特性。大型天线阵列含有很多的辐射单元,单独应用矩量法求解时,未知数太多,计算速度慢。而应用MOM-UTD混合方法,未知数的数量大大少于单独用矩量法时的未知数的数量。本文以振子组成的平面阵列为例,说明该方法如何应用。最后给出了数值解的结果,并与单独用矩量法得到的结果进行了比较。比较表明,该方法是有效的、准确的。     

Review of hybrid methods on antenna theory

Hybrid methods are robust analysis tools for a large class of complex scattering and radiation problems not amenable to traditional classical methods. In the hybrid technique, a complex radiator is decomposed into parts solved by a combination of numerical and asymptotic methods. Three methods are reviewed here: the hybrid MM/Green’s function method; the field-based hybrid method which combines the method of moments (MM) and the geometrical theory of diffraction (GTD); and the current-based hybrid method which incorporates MM, physical theory of diffraction (PTD), and the Fock theory. The domain of applicability of each method is illustrated with examples.     

Improvement of the PO-MoM hybrid method by accounting for effectsof perfectly conducting wedges

A correction of the conventional physical optics (PO) current close-to-perfectly conducting wedges based on an application of the uniform geometrical theory of diffraction (UTD) is presented. This improved PO current is used in a hybrid formulation in combination with the method of moments (MoM) to deal with three-dimensional scattering bodies of arbitrary shape. The accuracy of this hybrid method is demonstrated by some examples. As opposed to an application of the physical theory of diffraction (PTD), only surface current densities and no fictitious electric and magnetic line currents along the edges are involved which allows a uniform treatment of the MoM and the PO region by expressing the surface current density as a superposition of basis functions defined over triangular patches     

Electromagnetic scattering by a two-dimensional wedge composed ofconductor and lossless dielectric

Electromagnetic scattering by two-dimensional wedges composed of perfectly conducting and lossless dielectric material is considered. Heuristic geometrical theory of diffraction type diffraction coefficients are presented and a hybrid moment-method/physical-optics technique is developed to verify the accuracy of the proposed diffraction coefficients. The purpose is to show that the heuristic approach can yield acceptably accurate results for a number of composite wedge geometries, rather than to present rigorous diffraction coefficients for the composite wedge per se. Calculated results are presented in which the results obtained by means of the two methods are compared. Very good agreement is achieved for a variety of wedge geometries     

Current-based hybrid analysis for surface-wave effects on largescatterers

Current-based hybrid analyses combine the method of moments (MM) with Ansatz currents derived from high-frequency methods such as physical optics, physical theory of diffraction (PTD), geometric theory of diffraction (GTD), and the Fock theory. The author introduces an analysis that incorporates a surface-wave basis set into the hybrid formulation. This approach substantially improves the modeling of nonspecular effects caused by surface waves. The discussion emphasizes the accurate representation of surface wave currents and the reduction of computational efforts in comparison with the conventional MM techniques. Scattering calculations for bodies of revolution (BORs) and two dimensional surfaces demonstrate the effectiveness of the analysis presented for large scatterers     

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     

Comparison of different order GTD solutions of double-edgediffraction problem

A second order diffraction coefficient for the uniform geometrical theory of diffraction (GTD) is obtained explicitly for two knife edges in terms of the usual complex transition function (a modified Fresnel integral). The results from conventional GTD (zero order), slope diffraction GTD (first order), and second order GTD are compared with those obtained from physical optics (PO), which uses the complex Fresnel double integral. The results from second order GTD are close to those from PO in most of the cases studied     

A hybrid asymptotic solution for the scattering by a pair ofparallel perfectly conducting wedges

The overlapping transition regions of the double diffraction by a pair of parallel wedge edges are considered for the hybrid case where the gap between the edges is small compared to the distances from the source and the observation point (plane-wave-far-field limit) and the scatterer as a whole is large (or infinite). A closed-form asymptotic solution for the scattered field continuous at all angles of incidence and scattering is constructed for this case. The peculiar feature of this solution is a hybrid representation of the field singly diffracted by the first wedge: a part of it is described by a nonuniform, geometrical theory of diffraction (GTD) expression, while the other part is described in terms of the uniform theory of diffraction (UTD). The rest of the diffracted ray fields are described by nonuniform expressions, with singularities mutually canceling on summation. This solution is applied to the scattering by a perfectly conducting rectangular cylinder with appropriate geometrical parameters, and agreement with moment method calculation is demonstrated