A hybrid FEM/MOM technique for electromagnetic scattering andradiation from dielectric objects with attached wires

A hybrid formulation is presented, which combines the method of moments (MOM) with the edge-based vector finite element method (FEM) to solve electromagnetic radiation problems from structures consisting of an inhomogeneous dielectric body of arbitrary shape attached to one or more perfectly conducting bodies. While either method alone fails to model these structures efficiently, a combination of both finite element and moment methods provides an excellent way to solve these problems. The FEM is employed to handle the interior domain of inhomogeneous dielectric bodies and the method of moments is used to develop surface integrals that relate the field quantities on boundary surfaces with the equivalent surface currents. These integral equations are then coupled to the finite element equations through the continuity of the tangential magnetic fields across the hybrid boundaries     

Numerical Analysis of Open-Ended Coaxial Lines

Numercal methods are applied in the analysis of coaxial structures used as sensors for in vivo permittivity studies of biological substances. The methods used for the solution of the resulting static conductor-dielectric problems are the Finite Element Method (FEM) and the Method of Moments (MOM) applied to a pair of coupled integral equations. A linear model which relates the sample permittivity to the fringing field capacitance of the sensor is discussed and values of the model parameters are calculated for different types of sensors.     

Hybrid analysis of reflector antennas including higher order interactions and blockage effects

The analysis of a reflector antenna system consisting of a feeder, a sub-reflector, and a main-reflector in microwave frequency bands, where the electrical dimensions of the antenna become prohibitively large for the use of a rigorous numerical method, has been performed by high-frequency asymptotic techniques (HFATs). As a result, the radiation patterns and input impedances of the antenna system were calculated based on an approximation: the radiation characteristics of the feed, sub-reflector and main-reflector are independent from each other. In this study, as an effort to alleviate the inaccuracy due to the exclusion of higher order mutual interactions existing among those subsystems, three different hybrid methods [finite-element method/method of moment (FEM/MOM) + physical optics (PO), FEM/MOM + geometrical theory of diffraction (GTD), and FEM/MOM + PO + physical theory of diffraction (PTD)] are introduced in the context of an iterative algorithm. The interactions between the feed and sub-reflector are accounted by a hybrid method which combines the FEM with the MOM; FEM/MOM. Whereas, the interactions between the objects in the FEM/MOM domain and the main-reflector are taken into account through the iteration: the fields and currents in the FEM/MOM domain are updated using the fields and currents obtained from the HFAT domain and vise-versa. These three methods are applied to two-dimensional reflector configurations, and corresponding results are compared in terms of accuracy and efficiency. The accuracy of the hybrid methods, especially those of FEM/MOM + GTD and FEM/MOM + PO + PTD, is found to be comparable to that of a rigorous numerical method. Furthermore, their computational costs are almost independent to the size of the main-reflector and to the distance from the feed point to the main-reflector.     

外推技术结合矩量法应用于二维介质柱RCS计算

基于Richardson外推(Extrapolation)提出了一种提高精度和快速计算任意二维介质柱体的雷达散射截面(RCS)外推技术和矩量法(MOM)相结合的方法(RE—MOM)。首先用二层粗细有序网格对介质柱体截面剖分。接着采用矩量法对相应二维介质柱体的电场积分方程求解，得到介质体在某一平面入射波照射下各自的电场向量，通过外推技术获得介质柱体在这一人射波照射下细网格上高精度的电场向量，进而计算出RCS。文中计算了几个例子，并与其他数值计算方法进行了比较，结果表明RE—MOM方法是正确和有效的。     

Surface integral equation method for the analysis of an obliquelystratified half-space

The radiation of a source in the presence of an obliquely stratified half-space is studied using the surface integral equation method. A generalized extinction theorem for the obliquely stratified half-space problem is derived, which gives eight surface integral equations for the fields. The Green's functions for the stratified media are found by a semianalytical method. These surface integral equations can be used to solve the rather complicated two-dimensional problem by the one-dimensional finite element method (FEM), which saves computer memory and computation time compared to the conventional two-dimensional FEM. for some special cases, the results obtained by this method are compared with those obtained by the numerical mode matching method and the Fourier integral technique. Excellent agreement has been observed between them. This method is general for any obliquely stratified half-space with arbitrarily many layers in each region     

小波矩量法分析环形微带缝隙天线*

将矩量法和小波变换理论结合起来,应用于求解电磁场积分方程,分析计算了环形微带缝隙天线磁流分布、驻波、阻抗特性和辐射方向图,通过用小波基代替一般的分域基矩量法中的权函数和基函数,使矩量法中与算子相对应的阻抗矩阵变成为大量元素为零的稀疏矩阵,减小了数值方法对存储量的要求,在达到允许精度的前提下,使计算量显著降低。文中给出计算实例,验证该方法,计算结果与用一般矩量法计算结果和实际测试结果相比,吻合较好。     

关于ICCG与有限元结合时计算特性的讨论

本文给出了ICCG的复数形式,并将其应用于电磁场散问题的数值计算中.讨论了不同性态的矩阵方程用ICCG求解的特点.并与其它算法进行了对比.同时文中还讨论了有限元网格优化及预选参数Ψ对ICCG收敛速度的影响.结果表明这种算法对解大型问题.尤其是对大型稀疏阵非常有效.     

Circuit models for power bus structures on printed circuit boards using a hybrid FEM-SPICE method

Power bus structures consisting of two parallel conducting planes are widely used on high-speed printed circuit boards. In this paper, a full-wave finite-element method (FEM) method is used to analyze power bus structures, and the resulting matrix equations are converted to equivalent circuits that can be analyzed using SPICE programs. Using this method of combining FEM and SPICE, power bus structures of arbitrary shape can be modeled efficiently both in the time-domain and frequency-domain, along with the circuit components connected to the bus. Dielectric loss and losses due to the finite resistance of the power planes can also be modeled. Practical examples are presented to validate this method.     

一维FSS电磁散射宽带特性的快速计算

基于渐近波形估计（AWE）技术和矩量法（MOM），快速分析了一维频率选择表面（FSS）的宽带电磁散射特性，首先采用MOM法将平面波照射下FSS的电场积分方程（EFIE）转化为关于感应电流的矩阵方程，并由该方程确定频率导数矩阵方程（MEFD）；再在所考虑的频带内的某一给定频率处求解MEFD，得到给定频率处的频率导数感应电流；最后根据Pade逼近理论由给定频率处的频率导数感应电流确定周期性结构在任意频率入射波照射下的感应电流，根据FSS上的感应电流及谱域Floquet谐波模计算FSS的电磁散射宽带特性，计算结果表明，AWE能有效逼近MOM逐点扫描计算的结果，同时在计算速度上可加快十几倍。     

光电器件仿真分析中的COCG高效迭代算法

对光电器件采用FEM/EFIE仿真分析所产生的线性系统的迭代求解算法进行了研究。与目前普遍使用的迭代法不同,针对FEM/EFIE系数矩阵的特点,提出了采用求解复对称且非正定的线性方程组的共轭正交共轭梯度（COCG）算法来进行高效迭代求解。数值实验基于对波导元件分别采用矢量有限元法（FEM）和电场积分方程法（EFIE）得到的两类典型线性系统进行迭代求解。结果表明：与常规迭代法相比,COCG在求解速度和内存使用上的性能优势非常明显,从而能较大地提高仿真效率。     

A systematic treatment of conducting and dielectric bodies witharbitrarily thick or thin features using the method of moments

A systematic procedure for modeling electromagnetic scattering problems involving bodies with electrically thin features is discussed. The scattering bodies are represented using standard surface integral equation formulations and solutions are obtained via the method of moments (MOM). It is demonstrated that accurate evaluation of the moment matrix elements is critical for obtaining accurate solutions for scatterers having thin features. It is also shown (by numerical example) that some of the various surface integral formulations remain valid and can be used to obtain accurate scattering results for arbitrarily thin dielectric and conducting features. The use of the systematic approach for such problems is illustrated by incorporating the procedures into a two-dimensional (MOM) program. Sample results illustrating the technique's utility and validity are provided     

埋于介质体中二维导体目标成象的迭代方法

本文应用一种迭代方法实现了埋于二维均匀介质体中理想导体目标几何构形的重建。在导出介质体与导体混合目标散射边界积分方程的基础上，利用Ｎｅｗｔｏｎ－Ｋａｎｔｏｒｏｖｉｃｈ方法和矩量法建立逆散射基本方程。为克服病态问题，连续采用多方面ＴＭ平面波照射目标以获取足够的信息，并通过迭代方法求解。最后、给出的一些散射目标的重建结果表明本方法的可行性，同时研究了噪声对重建结果的影响。     

A hybrid finite-element method for axisymmetric waveguide-fed horns

A new method for finding radiation patterns and the reflection coefficients associated with an axisymmetric waveguide fed horn is presented. The approach is based on a hybrid finite element method (FEM) wherein the electromagnetic fields in the FEM region are coupled to the fields outside by two surface integral equations. Because of the local nature of the FEM, this formalism allows for the presence of inhomogeneities to be included in the problem domain. The matrix equation which results from the application of this method is shown to be complex-symmetric. Comparisons of calculated and measured data for two different horns show good agreement     

周期性结构电磁感应电流宽带特性的快速计算

采用MOM法将周期结构的电场积分方程转化为关于感应电流的矩阵方程和频率导数矩阵方程，并根据Pade逼近理论由给定频率处的频率导数感应电流确定周期性结构在任一频率入射波照射下的感应电流，进而计算周期性结构的电磁感应电流宽带特性。计算结果表明，AWE在计算速度上比MOM可加快十几倍。     

Magnetic field integral equation at very low frequencies

It is known that there is a low-frequency breakdown problem when the method of moments (MOM) with Rao-Wilton-Glisson (RWG) basis is used in the electric field integral equation (EFIE); it can be solved through the loop and tree basis decomposition. The behavior of the magnetic field integral equation (MFIE) at very low frequencies is investigated using MOM, where two approaches are presented based on the RWG basis and loop and tree bases. The study shows that MFIE can be solved by the conventional MOM with the RWG basis at arbitrarily low frequencies, but there exists an accuracy problem in the real part of the electric current. Although the error in the current distribution is small, it results in a large error in the far-field computation. This is because a big cancellation occurs during the far field computation. The source of error in the current distribution is easily detected through the MOM analysis using the loop and tree basis decomposition. To eliminate the error, a perturbation method is proposed, from which a very accurate real part of the tree current has been obtained. Using the perturbation method, the error in the far-field computation is also removed. Numerical examples show that both the current distribution and the far field can be accurately computed at extremely low frequencies by the proposed method.     

Nonlinear analysis of ferrite-core circuits

An analysis is presented of the behavior of magnetic-core circuits employing rectangular-hysteresis-loop ferrite toroidal cores, and switched by a constant-current source. The analysis embraces simple magnetic-core circuits with various loads, multi-path-core circuits, cascaded-core circuits and air-gap-core circuits. The method of analysis presented is based upon an extension of A. Papoulis' unpublished work. It is known that the response or terminal properties of various magnetic-core circuits can be described analytically in a set of nonlinear equations. A form of graphical analysis is used to solve the nonlinear differential equations, and phase-plane trajectory is used to solve the nonlinear integral equations. Experiments have been conducted to verify the theoretical methods; theoretical calculations proved to be a close approximation to measured values.     

Theoretical modeling of cavity-backed patch antennas using a hybridtechnique

A hybrid technique that combines the method of moments (MoM) and the finite element method (FEM) to analyze cavity-backed patch antennas is presented. This technique features the use of FEM in solving the electromagnetic field distribution in the cavity and the use of MoM in solving integral equations outside the cavity. The results of MoM and FEM are combined through the continuity conditions on the boundary of the cavity. Due to the flexibility of FEM, complex cavities filled with inhomogeneous media can be analyzed by this technique. The results obtained by this hybrid technique are compared to the finite difference time domain (FDTD) results and good agreement is found