Finite-Element Analysis of Dielectric Waveguides with Curved Boundaries

The modes of dielectric waveguides with curved boundaries are computed efficiently using a curved-sided (isoparametric) second-order finite element rather than the more usual triangular element. A novel way of placing the virtual boundary is described. Results are obtained for dielectric rod and elliptical waveguides, and compared with earlier results. The method is used to analyze a single-mode fiber-optical coupler.     

曲边介质波导的有限元分析

本文应用曲边有限元方法有效地计算了曲边质波导的色散特性，编制了相应的计算程序,应用本文方法计算得到的椭圆旬质波导和组合椭圆介质波导的主模和高次模的色散曲线与文献[2],[3]的结果相当吻合。     

Vectorial Finite-Element Method Without Any Spurious Solutions for Dielectric Waveguiding Problems Using Transverse Magnetic-Field Component

An improved finite-element method for the analysis of dielectric waveguiding problems is formulated rising the transverse magnetic-field component. In this approach, the divergence relation /spl nabla/ · H = 0 is satisfied and the spurious, nonphysical solutions which have been necessarily included in the solutions of earlier vectorial finite-element methods are completely eliminated in the whole region of a propagation diagram. To verify the accuracy of the present method, numerical results for a rectangular metallic waveguide half filled with dielectric are presented and compared with exact and earlier finite-element solutions. Dielectric rectangular waveguides are also analyzed for both isotropic and anisotropic cases.     

Finite-Element Analysis of Dielectric-Loaded Waveguides

A finite-element analysis in which nonphysical spurious solutions do not appear has been established to solve the electromagnetic field problem of the closed waveguide filled with various anisotropic media. This method is based on the approximate extremization of a functional, whose Euler equation is the three-component curlcurl equation derived from the Maxwell equations, with a new conforming element. Specific examples are given and the results are compared with those obtained by exact solutions and longitudinal two-component finite-element solutions. Very close agreement was found and all nonzero eigenvalues have been proved to have one-to-one correspondence to the propagating modes of the waveguide.     

A Nonlinear Finite-Element Leaky-Waveguide Solver

A novel hybrid finite-element method for the analysis of leaky-waveguide structures is presented. The possibly radiating structure is enclosed within a fictitious circular contour-C in order to truncate the infinite solution domain. The field in the unbounded domain, outside contour-C, is expressed as a superposition of transverse electric and magnetic modes. Their radial dependence is expressed in terms of Hankel functions, which satisfy the radiation condition at infinity. The bounded area is discretized using hybrid node/edge elements for an accurate and efficient handling of the electric field vector wave equation. The transparency of the fictitious contour is ensured by enforcing the field continuity conditions according to the principles of a vector Dirichlet-to-Neumann mapping. The whole procedure yields a nonlinear eigenvalue problem for the complex axial propagation constant (beta). The nonlinearity is due to the appearance of beta within the argument of the Hankel functions. The final nonlinear problem is solved by employing a matrix Regula-Falsi algorithm. Initial guesses for the Regula-Falsi algorithm and a fast estimation of the eigenvalues spectrum are provided by a linear formulation based on a second-order approximation (beta/k_o)² Lt 1. The proposed method is validated against published numerical and experimental results for both leaky and surface wave modes.     

Finite-Element Solution of Unbounded Field Problems

An unbounded region is divided into local picture-frame regions where a partial differential-equation solution is obtained, with the remaining unbounded region represented by an integral equation. (The method permits the use of free-space Green's functions, and thus special problem-dependent Green's functions need not be found.) The integral equation is formulated as a constraint upon the local picture-frame solutions, whence these local solutions are solved directly by a variational method, using finite elements, in a manner such that the problem of the Green's-function singularity is side-stepped. The technique is applicable where sources and media inhomogeneities and anisotropies are local, and can all be placed within one or several picture frames. It is in these cases that the integral-equation approach is at a particular disadvantage, and the use of a partial differential-equation technique is advisable if not necessary. Examples presented include the static and harmonic fields of a parallel-plate capacitor, a microstrip line on a dielectric substratum, and a radiating antenna with dielectric obstacles.     

矩形波导不连续性的有限元分析

本文应用Gelerkin有限元法对矩形波导H面和E面不连续性问题进行了研究,编制了一个通用的计算机程序.对矩形波导H面弯曲、E面弯曲以及T型结头进行了计算机辅助设计,理论计算与测试结果吻合很好,证明了本文方法的正确性.     

Finite-Element Time-Domain Simulation of Electric Discharges

A formulation to deal with materials having dispersive and nonlinear characteristics in the finite-element time-domain method is proposed. The approach is illustrated by an electric discharge simulation in a spark gap switch based on the collision plasma vector differential equation with a polarization current dependent resistivity. The simulated voltage response across the spark gap switch matches the waveform of the measured curve and allows the extraction of the unknown plasma frequency for the electric discharge in air.     

操作控制台有限元分析

采用有限元分析软件ANSYS模拟实际工况对操作控制台进行强度分析、模态分析和结构特性分析,通过环境试验验证分析结果的合理性.应用这种分析方法,可以为进一步的结构设计和优化设计提供理论依据和参考,提高设计效率.     

Polar Geometry Waveguides by Finite-Element Methods

For waveguides whose geometries are described as coordinate surfaces in circular polar coordinates, a finite-element method is used to derive base matrices over a triangular element in the polar geometry. These matrices are used to solve,mode problems in circular, sector, double-ridged circular, and spiral waveguides. The discussion is mainly in terms of cutoff frequency, bandwidth, and convergence.     

介质谐振器特性的有限元计算

本文应用有限元方法分析和计算了置于空气和不均匀介质中的圆柱形介质谐振器的谐振频率,以及介质谐振器与微带线的耦合参量。计算结果与现有文献的计算结果和实验结果相当吻合。     

Hybrid-Mode Analysis of Microstrip by Finite-Element Methods

A numerical analysis is presented in terms of finite elements of hybrid-mode propagation in closed microstrip. Two modes with zero frequency cutoff are described; one is a quasi-TEM mode and the other a surface mode. Also investigated is a third mode which corresponds to the lowest order waveguide mode in the absence of the strip.     

A General High-Order Finite-Element Analysis Program Waveguide

A very general computer program for determining sets of propagating modes and cutoff frequencies of arbitrarily shaped waveguides is described. The program uses a new method of analysis based on approximate extremization of a functional whose Euler equation is the scalar Helmholtz equation, subject to homogeneous boundary conditions. Subdividing the guide cross section into triangular regions and assuming the solution to be representable by a polynomial in each region, the variational problem is approximated by a matrix eigenvalue problem, which is solved by Householder tridiagonalization and Sturm sequences. For reasonably simple convex polygonal guide shapes, the dominant eigenfrequencies are obtained to 5-6 significant figures; for nonconvex or complicated shapes, the accuracy may fall to 3 significant figures. Use of the program is illustrated by calculating the propagating modes of a class of degenerate mode guides of current interest, for which experimental data are available. Numerical studies of convergence rate and discretization error are also described. It is believed that the new program produces waveguide analyses of higher accuracy than any general program previously available.     

基于有限元方法的螺旋天线设计

研究了一种用于中短距离通信的螺旋天线,分析了螺旋天线特别是轴向模螺旋天线的基本电磁辐射特性,介绍了有限元方法的基本理论和数值计算过程,并结合有限元法对螺旋天线进行了设计、优化,仿真出该天线的电参数和辐射方向图,然后将设计的天线模型进行通信实验。实验表明圆极化的轴向模螺旋天线通信质量良好,完全达到设计要求。     

科普的境界

我们都希望能够在本届博览会上看到好于往届的景象,因为在科技与社会快速发展的今天,无论是在科技馆里,还是在电视屏幕或科普画廊以及图书架上,我们实在需要越来越多的不断创新的科普产品,以适应社会发展和广大公众的要求。实现这个目标,不仅是我们对科普产品创作者和生产厂家、出版商的期待,也是我们全体科普工作者的责任。要担负起这样的责任,在很大程度上又取决于我们对任何一件（部）科普产品创作的依据、目的和意义等基本问题的认识与理解。     

EBG结构在曲面共形天线中的应用

利用Mushroom型EBG结构的等效电路和Bragg反射条件,设计了三种曲面EBG结构。并通过刻蚀和加载的办法将它们应用在曲面共形天线中。经过建模仿真,并且与普通的天线进行比较,发现附加EBG结构的共形天线的回波损耗得到了很好的抑制,辐射方向图也取得了很好的改良。天线的前向辐射有了不同程度的提高,背向和侧向辐射减小,在附虽EBG结构的二元阵中,阵元间的耦合效应也得到了有效的抑制。不过EBG结构单元不能距离天线贴片过近,否则也会引起新的互耦。     

Fast Waveguide Eigenanalysis by Wide-Band Finite-Element Model-Order Reduction

An efficient method for fast wide-band eigenmode analysis is presented in this paper. The finite-element solution space is projected to a subspace containing frequency-dependent information obtained at a single frequency by a Lanczos algorithm and modified perturbation theory, resulting in a single-point reduced-order model accurate over an extremely wide frequency range. A numerical procedure is developed to extract a desired mode from the reduced-order model for fast frequency sweep and is then applied to several practical problems, which demonstrate the solution accuracy and computational efficiency of the proposed method.