鳍线阻抗不连续性的混合模散射特性

本文用混合模展开鳍线中的本征场,并应用谱域法确定主模和高次模的传播常数和谱域中的本征场,然后结合模匹配法分析鳍线阻抗不连续性的混合模散射特性。文中给出计算的单鳍前30个模,双鳍前20个模的传播常数和阻抗不连续性的主模散射参数,计算结果与文献发表的结果一致。有关数值收敛性问题亦在文中进行了讨论。     

求解非均匀平面波导导模的一种新方法

本文给出一种新方法,用多层平板波导逼近非均匀平面波导,借助递推公式用牛顿切线法求解本征值方程,以求出非均匀平面波导导模的传播常数与模场分布。本方法优点在于程序简短通用,计算工作量小,求得结果与精确数值解十分吻合(直至近截止区)。本文给出了各种类型的非对称与对称渐变折射率平面波导的结果。     

用直线法分析圆截面S弯管的雷达散射截面

本文首次用直线法分析计算了电大尺寸波导中本征模的截止波数及场分布函数。由此求出的直圆管RCS分布曲线,与已知的计算和测试曲线在主要关心的角度范围内吻合很好。在此基础上依据耦合波理论求得本征模在弯波导段中的传输参量,最后由Stratton—Chu积分求得S弯管的后向散射场。计算及其与测试结果的比较表明,本文方法省时、简便且有较高精度,是计算圆截面S弯管雷达散射截面的一种有效方法。     

手征光纤中导模的色散特性

从手征介质中的电磁场本构关系出发，利用麦克斯韦方程组，对纤芯和包层都是手征介质构成的阶跃型手征光纤进行了解析求解，导出了模式场解和特征方程。用数值方法研究了纤芯和包层的手征导纳对手征光纤中导模的归一化传播常数、群延迟、波导色散等特性的影响。     

手征等离子本填充圆波导的传播特性

本文在柱坐标系中导出了手征等离子体波导内横向场量与纵向场量之间的关系，给出从向场量的波动方程，利用波导壁上的电场边界条件，建立了手征等离子体介质填充的圆波导传播常数的特征方程，计算得到了几种低次模式的传播常数随归一化波导半径及材料参数的一系列变化曲线，分析得出了若干有意义的结论。     

部分填充手征负折射率介质的平行板波导

部分填充手征负折射率介质的平行板波导中电磁波传输的导模特性进行了研究,给出了导模的场分布公式,推导出导模的特征方程.数值计算了导模的色散特性曲线、功率曲线和能流分布,探讨了手征负折射率介质层的厚度、手征参数等对导模特性的影响,发现了导模的一些奇异特性,如存在表面波模、功率流动方向与相位传播方向相反的后向波、功率储存、传播常数三值、模式交叉等现象,还发现此波导中存在电磁波传播的禁带.     

均匀直波导内的并矢Green函数

给出并矢Green函数的定义及其在波导耦合与辐射中的应用例，给出直波导内本征模场的一般表达式，在本征模是完备基的前提下，用极简单的办法得出四个并矢Green函数的一般表达式，给出了本征模完备性的证明，指出：Ohm-Rayleigh法不仅方法繁琐，而且缺少完备性的证明，其结果尚未代回原方程予以检验，只能是一个猜想，最后介绍Green函数的广义函数理论概要，以解释“源点场发散”的原因和处理原则。     

一种有效的三维光波导传输模式的数值计算方法

研究了一种有效的三维光波导传输模式本征值和本征向量的数值计算方法--反向迭代法,并用matlab语言实现了该数值计算方法对三维光波导基模和高阶模的求解. 本文所研究的反向迭代法是反幂法的一种改进形式.先从反向迭代法的基本数学原理入手,分析了反向迭代法的数值计算过程,以及收敛性和稳定性的判断.接下来,用波动光学的方法分析了三维波导的传输模式,得到了直角坐标下的亥姆霍兹方程,并对亥姆霍兹方程做了离散化处理.然后,将反向迭代法用于该方程的数值求解过程,并得到了三维波导所有可能的传播模式.由于该数值计算过程是直接对三维波导的亥姆霍兹方程进行处理,因此它对任意结构的三维波导都是适用的.通过对不同结构波导的计算表明反向迭代算法是一种处理三维光波导本征值与本征向量有效的计算方法,它不仅能求解三维光波导基模模式,而且也能较容易地搜索到高阶模模式,而这是其它数值计算方法很难办到的. 最后,为了验证所求传输模式数值解的正确性,用FDTD(时域有限差分)算法模拟了这些传输模式在三维光波导的传播过程.通过对输入场和传播过程中不同位置场分布的比较,结果表明该算法具有比较理想的精度.(PD8)     

手征等离子体填充圆波导的传播特性

本文在柱坐标系中导出了手征等离子体波导内横向场量与纵向场量之间的关系,给出求解纵向场量的波动方程.利用波导壁上的电场边界条件,建立了手征等离子体介质填充的圆波导传播常数的特征方程,计算得到了几种低次模式的传播常数随归一化波导半径及材料参数的一系列变化曲线,分析得出了若干有意义的结论.     

任意截面形状介质填充波导高次模求解的快速边缘元算法

本文提出了一种精确求解任意截面形状介质填充波导高次模的快速边缘元算法.数值实验表明:与以往算法相比,此算法所用内存巨幅减小,计算效率极大提高.具体数值研究了波导高次模求解精度和剖分疏密的关系.本文还计算了矩形空波导、条状介质填充波导、以及方块介质填充波导的本征模,与解析解或公布结果比较,证实本算法计算精度极高且不含伪解.最后本文还用开发的程序具体研究了内壁涂层波导的本征模.     

Full-wave analysis of dielectric waveguides using tangential vectorfinite elements

A novel method is presented for the analysis of dielectric waveguides. This method provides four major new contributions: (1) a transformation of variables is introduced that allows propagation constants to be computed directly; (2) H₁ (curl) tangential vector finite elements are applied to dielectric waveguides to obtain reliable approximate electromagnetic fields; (3) the Lanczos algorithm is modified to solve the required eigenmatrix equation efficiently; and (4) the reaction principle is used to provide a posteriori error estimates for use in adaptive mesh refinement. The method produces reliable solutions and applies to structures that contain both electric and magnetic inhomogeneities. The answers are refined adaptively to generate waveguide eigenmodes to a specified accuracy. Numerical results of an image guide, a microstrip transmission line, and a pedestal-supported stripline are shown. Computed solutions agree very well with previously published results     

Rigorous boundary integral equation solution for general isotropicand uniaxial anisotropic dielectric waveguides in multilayered mediaincluding losses, gain and leakage

Bounded and leaky eigenmodes of arbitrary shaped polygonal dielectric waveguides embedded in a multilayered medium are determined based on a rigorous full-wave analysis. The dielectric waveguides consist of isotropic or uniaxial anisotropic material. Losses and gain inside the layers and the waveguides are allowed. The eigenmodes are determined with a boundary integral equation technique in conjunction with the method of moments. Results for the propagation constants are presented for a number of waveguides and, where possible, compared with published data. Special attention is devoted to the transition from a dielectric waveguide to a perfectly conducting waveguide when the loss tangent of the waveguide material changes from zero to infinity     

Electromagnetic fields in circular bends of slab waveguides

A rigorous theory for analysis of radiation and transmission of electromagnetic waves in uniformly curved sections of slab waveguides is presented. Eigenmodes with continuous eigenvalues are defined for the sectorial region, which includes the circularly bent section of slab waveguides. General fields in the sectorial region can be expanded in terms of these eigenmodes. The theory is applied to the analysis of transient fields in the circularly bent section of a slab waveguide connected to a straight section. Numerical examples of radiation patterns and field distributions are presented for the TE₀-mode incident from the straight section     

Eigenmodes of a 2D array of coupled slot lines in the impedance approximation

A 2D periodic array of coupled slot transmission lines is considered in the approximation of equivalent boundary conditions. The eigenmode problem for an array operating in the quasi-periodic mode is formulated and solved. The dispersion equation for eigenmode propagation constants and expressions for eigenmode fields are obtained. The behavior of eigenmodes in a frequency band and in a range of values of geometric parameters is analyzed. The orthogonality of eigenmodes is shown. Theoretical results are compared to the results of numerical calculation performed with the use of electromagnetic simulation systems.     

Analysis of Open Dielectric Waveguides Using Mode-Matching Technique and Variational Methods

The mode-matching technique is employed for computing the propagation constants and field distributions of an inverted strip dielectric waveguide. The results derived in this manner are further improved by using variational formulas expressly designed for open dielectric waveguides. Illustrative numerical results are presented and compared with an experimental measurement as well as those based on approximate methods found in the literature.     

Transmission and attenuation of vector modes in uniformly bentcircular hollow waveguides for the infrared

Electric field distributions and attenuation constants of the eigenmodes in uniformly bent circular hollow waveguides have been evaluated based on a vector wave equation deduced from Maxwell's equations. A diagram representation of the parameter describing mode properties is introduced. It is numerically shown that vector modes gradually approach linearly polarized modes when the bending radius becomes small. A relation between attenuation constants in sharply bent circular and slab hollow waveguides is also discussed where the electric fields concentrate near the outer edge of the core     

An assessment of finite difference beam propagation method

A finite-difference beam propagation method (FD-BPM) is outlined and assessed in comparison with a conventional beam propagation method (FFT-BPM) which uses fast Fourier transformation. In the comparative study three straight waveguides with different index profiles that are frequently encountered in integrated optics are utilized. Using both methods normalized effective index values of the eigenmodes of these waveguides are calculated and compared with the exact values obtained from analytical expressions. As a further accuracy criterion, the power loss due to numerical errors when an eigenmode of a waveguide is excited is evaluated. Based on this comparison the accuracy, computational efficiency, and stability of the FD-BPM are assessed     

Numerical Analysis of the Rectangular Dielectric Waveguide and its Modifications

Dielectric waveguides suitable for millimeter and submillimeter wave integrated circuits are analyzed by applying the generalized telegraphist's equations. The dielectric waveguides treated in this paper are the rectangular dielectric image line, the cladded rectangular dielectric image line, the insulated image guide, and the strip dielectric guide. Numerical results of the propagation constant, the power distribution, and the field configuration in these dielectric waveguides are presented. Values for the propagation constants obtained by our method are compared with other theoretical results. Although this work is based on a closed waveguide model, it may be applicable to wide classes of dielectric waveguides with arbitrary dielectric profiles and cross sections.     

Eigenvalue analysis of curved waveguides employing FDFD method in orthogonal curvilinear co-ordinates

A two-dimensional finite difference frequency domain eigenvalue method employing orthogonal curvilinear co-ordinates is established. Its main strength is the accurate modelling of curved interfaces enabling the accurate evaluation of the complex propagation constants of curved waveguides. Numerical results for multilayer-multiconductor microstrip lines printed on curved substrates prove the validity of the method.     

Propagation in cylindrical fibres with anisotropic crystal cores

Expressions for the fields and propagation constants in cylindrical dielectric waveguides with umaxial crystal cores are found. The propagation constants of biaxial-crystal-cored guides are then deduced from a coupled-mode analysis, using the uniaxial solutions as ideal modes.