四分量二维紧凑格式频域有限差分方法对粗糙导体表面导波结构的分析

文章利用四分量紧凑格式的二维频域有限差分方法（2-DFDFD）,结合等效表面阻抗边界条件（SIBC）,对粗糙导体表面导波结构的传输特性进行数值分析。根据等效表面阻抗边界条件,可以方便地计算边界上的切向场。只要求出本征方程,在给定频率上的传播常数就可以作为其特征值而被求得。     

角锥阵列的散射特性

借助于Floquet定理和空间谐波理论对周期性角锥阵列的散射特性进行了研究,分析了散射场的形成机理,讨论了阵列边缘切断效应对散射特性的影响.采用时域有限差分(FDTD)方法和周期性边界条件对吸波材料锥体阵列和微波黑体锥体阵列的散射场进行了计算,分析了RCS和微分散射系数的空间分布随阵列结构参数、阵列表面吸波涂层参数以及入射波频率的变化关系,给出了锥体内部和口面的场分布.     

偏心介质棒加载圆波导模式分析

本文基于柱谐基函数展开,对偏心介质棒加载的圆波导模式进行分析.利用Bessel函数的加法定理,在边界上进行场匹配,获得关于诸传播常数K_z的方程.对方程进行级数截断后,可以方便地解出该波导的各种传播模式,具有收敛性可靠,结果精确、计算量小的特点,比PMM和LSBRM更为可靠易行.     

有耗介质导波结构的高次杂交四边形边缘元分析

本文提出了一种高次杂交四边形边缘元方法。讨论了这种高次杂交边缘元的有限元空间构造，给出了其形函数的显形表达式。这种方法不仅消除了伪解而且能直接求解传播常数，从而无需迭代便能分析有耗介质导波结构的传输特性。对矩形导和条形介质填充波导本征模传播常数的计算表明这种高次杂交边缘元的计算精度比低次杂交边缘元要高出一个量级。     

波导结和波导-喇叭辐射器有限元分析导波数值边界条件及其应用

作为开域电磁场问题偏微分方程解法的一个重要方面,本文提出导波致值边界条件的概念和算法。本文着重讨论二维的具有平面导体边界的导波系统的散射和辐射问题,并以此表明基于数值边界条件的偏微分方程的数值解法,将为波导-喇叭辐射器的准确分析开辟了新的理论途径。     

边界条件微扰法计算非理想波导的传播常数

考虑到非理想导体波导壁金属损耗对传播常数的影响,对理想金属边界条件进行一阶近似微扰,得到了非理想波导的传播常数。和传统微扰法相比,能够在截止频率附近较为精确地计算衰减常数,也适用于导体损耗较大的情况;同时能给出非理想导体波导壁对相位常数的影响。将结果与Ansoft HFSS软件的仿真结果进行比较,两者具有较好的一致性。同时给出了边界条件微扰法解与解析解及传统微扰法解在一定条件下的联系,表明边界微扰法比解析法实现简单,比传统微扰法具有更广泛的适用性。     

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.     

FDTD中的一种新截断边界-STWBC

本文提出了一种新的边界条件:驻波-行波边界条件(STWBC).这种边界条件是在计算域外附加理想导电(磁)壁进行截断,运用反射原理,将边界处的驻波转化为行波,保持计算域内的行波状态,在有限空间内有效模拟出无限大的电磁散射空间.文中给出了该边界条件在FDTD中的差分迭代式,以及二维数值实验结果,并与PML边界和单向波边界进行了比较.由于该边界比单向波边界所需计算空间小,数值稳定性好,同时不象PML边界,需要进行场量分离和附加额外的吸收层,因此计算效率较高.     

波导模场分布采用模式匹配的PML处理方法

理想匹配层(PML)是近年来迅速发展起来的一种非常有效的吸收边界.本文基于模式匹配法将PML吸收边界条件用于平面光波导结构计算中,从理论上分析了PML吸收边界条件的有效性,并在PML边界条件下模拟计算了一个三段平面光波导结构的模场分布.     

分析无限平面金属栅电磁散射问题的一种新方法

本文基于直线法和Floquet定理提出了一种分析无限平面金属栅周期结构电磁散射问题的新方法。数值结果与谱域法结果和实验结果一致,但本文方法具有数学模型简单,计算量小等优点。     

Electromagnetic wave propagation in multilayer dielectric periodicstructures

The propagation characteristics in multilayer dielectric periodic structures, that extends a previous analysis by introducing additional dielectric layers, is presented. It is applied to propagating electromagnetic modes along the longitudinal and transverse directions of the structure's periodicity. The use of Floquet's theorem reduces the analysis to a single cell of the propagating fields for both, TE and TM polarizations. Results showing the effect of varying the layers thickness and electric permittivity on the propagation constant and on the field distributions within each cell are presented as well as the band structure associated with the periodic structure     

Unit cell approach to full-wave analysis of meander delay line using FDTD periodic structure modeling method

Unit cell modeling is performed to determine the effect of electromagnetic coupling on the propagation characteristics of a meander delay line, which is widely used in printed circuit boards and packages. Since the design of a delay line must guarantee several tens of picosecond timing margin in modern high-speed packages and board level interconnections, a penetrating understanding of the meander effect is essential. The propagation delay, the characteristic impedance, and the stop-band characteristic of the meander delay line have been carefully investigated based on a full-wave analysis using the finite-difference time-domain (FDTD) periodic structure modeling method. The periodicity of the meander line is utilized based on Floquet's theorem, resulting in a reduction of the computational domain in the FDTD simulation and providing a unit cell model of the meander line. The unit cell modeling of the meander delay line shows the effect of electromagnetic coupling in meander line structure on the reduction of the propagation delay. Also, an analysis based on the unit cell modeling was confirmed by time-domain reflection/transmission measurements.     

A spectral-domain analysis of periodically nonuniform coupledmicrostrip lines

Periodically nonuniform coupled microstrip lines are analyzed on the basis of a numerical field calculation. As the case of the single nonuniform microstrip line described in an earlier paper, Floquet's theorem is used to express all field quantities in terms of their spatial harmonics. The boundary value problem is formulated in a rigorous way and then solved using Galerkin's method in the Fourier-transform domain. Numerical and experimental results are presented     

Modeling good conductors using the finite-difference, time-domaintechnique

Finite-difference, time-domain (FDTD) is based upon the assumption that field behavior between sample points (i.e., cell nodes) is linear; for propagation in lossless or low-loss materials, the assumption of linearity will be valid as long as the number of cells per wavelength is kept above some minimum value. For good conductors, where the wavelength decreases many orders of magnitude from its free-space size, and the fields are decaying exponentially, it becomes impractical to shrink the cell size so as to maintain linearity between cells. When the number of cells per wavelength criterion is violated at a boundary, FDTD will not yield correct estimates of reflection from, or transmission into, that boundary. The work presented details and provides validation for two approaches that can be used to achieve realistic results when modeling good conductors with FDTD using practical cell sizes. These approaches do not require modifications to the FDTD algorithms, and do not affect program execution times. Achieving accurate loss estimates will be of particular interest to those modeling resonant structures using FDTD     

时域有限差分法分析平面周期性结构电磁特性

本文阐述了如何用时域有限差分法分析平面周期结构的电磁特性.FDTD方法与周期性边界条件、吸收边界条件结合,构成分析各种周期性结构电磁特性准确、有效的通用工具.但为了在时域表示宽带信号的周期性边界条件,必须引入辅助场量并加以适当变形才可建立时域迭代式.文中以平面双周期频率选择表面为例,给出了计算思路和结果.     

Plane waves in FDTD simulations and a nearly perfect total-field/scattered-field boundary

The total-field/scattered-field (TFSF) boundary has been successfully used for a number of years to introduce energy into finite-difference time-domain (FDTD) grids. If the propagation of the incident field is grid-aligned, a perfect TFSF implementation can be realized by using an auxiliary one-dimensional FDTD simulation which models propagation of the incident field. Here "perfect" implies the incident field propagation exactly matches the way in which the field propagates in the FDTD grid. However, for propagation which is not grid-aligned, no similarly perfect implementation has previously been presented. This work provides a framework for a perfect TFSF boundary for pulsed plane waves which do not propagate in a grid-aligned fashion. To achieve this, homogeneous plane-wave propagation is rigorously quantified. Using this knowledge and a specification of the desired incident field, the dispersion relation is used to ascertain the incident field at any point in the grid. It is required to account for, unlike in the continuous world, the electric field, the magnetic field, and the wavenumber vector not forming a mutually orthogonal set. Group velocity is also considered because of its relevance to the implementation.     

Efficient analysis of periodic structures

An algorithm which allows the analysis of optical periodic structures with a very large number of periods with minimum numerical problems is presented, For this purpose the stable impedance transfer is combined with Floquet's theorem. Numerical results for a Bragg grating with up to 20000 periods are presented featuring the very moderate numerical effort     

Slow-Wave Coplanar Waveguide on Periodically Doped Semiconductor Substrate

A metal-insulator-semiconductor (MIS) coplanar waveguide with periodically doped substrate is described. An efficient numerical method is introduced in order to obtain the propagation constants and the characteristic impedances of the constituent sections of each period. Using the results, the characteristic of the periodic MIS coplanar waveguide is analyzed by Floquet's theorem. The theoretical study shows reduction of attenuation and enhancement of the slow-wave factor at certain frequencies, compared to the uniform MIS coplanar waveguide. This structure is experimentally simulated and shows good agreement theory.     

渐变开槽相控阵天线的FDTD分析

对UHF波段无限大开槽阵列天线进行了时域分析,应用Floquet原理对阵列的结构进行区域划分,同时采用时域有限差分法（FDTD）进行数值仿真,研究了作为相控阵天线应用时的频率和空间扫描特性,给出了数值计算结果,得到一些有参考价值的结论。