非Yee网格的FDTD法分析复杂媒质PBG结构的带阻特性

采用电、磁场各分量均位于网格中心的高阶时域有限差分法计算PBG结构的色散特性。对简单媒质问题的计算结果与采用Yee网格时域有限差分法所得一致，但更适合于分析含复杂媒质的问题。计算了三类磁各向异性PBG结构的色散特性曲线，指出：磁各向异性媒质都可明显增宽第一阻带；对称型磁各向异性还增多色散特性曲线中的阻带数，但旋磁型各向异性则不影响阻带数。     

辅助方程-双向隐式差分法的电磁散射研究

在辅助差分方程(ADEs)的基础上结合交替隐式时域有限差分方法(ADI-FDTD),提出ADEs-ADI-FDTD方法用以计算色散媒质的电磁散射问题。由于三维ADI-FDTD方法的复杂性,在此采用了全分裂场形式的场量以简化完全匹配层(PML)吸收边界的处理及在连接边界处入射场的加入。针对Debye型色散媒质,利用极化强度辅助差分系列方程推导了ADEs-ADI-FDTD方法中电、磁场的迭代方程及其相关参数表达式,最后通过对色散媒质和各向同性等离子体等物体进行仿真计算,计算结果显示了本文算法在时间上的高效性和精确性。     

基于帕德近似法模拟一般色散媒质电波传播的ADE-FDTD-CPML统一实现方案

为方便一站式处理常见几类各向同性、线性、无磁耗电色散媒质的电波传播问题,提出了一种ADE-FDTD-CPML统一实现方案:一是问题空间和吸收边界的统一处理;二是色散特性的统一建模:适用的媒质类型可以是单一的Havriliak-Negami(H-N)媒质、Davidson-Cole(D-C)媒质、Cole-Cole(C-C)媒质、Debye媒质、常规媒质或其任意组合;媒质属性可以是单极或多极的、有电耗的或无电耗的.该方案利用帕德(Padé)近似法,导出了一组整数阶辅助微分方程(ADEs),既克服了时域描述时遇到的分数阶导数困难,又展现了通用性好、复杂度低等优势.几个一维、三维算例解析、数值结果之间的对比,初步证实了统一实现方案的可行性和有效性.     

一种新颖的PBG宽阻带低通滤波器

 本文首次提出综合PBG结构和微带线结构两因素,来设计滤波器的概念.与普通PBG结构滤波器不同的是,本文采用具有T形和十字形短截线的微带线代替直线微带线,在接地板上只需刻蚀一列PBG结构即可构成宽阻带低通滤波器.文中以T形短截线PBG结构的低通滤波器为例,运用时域有限差分法(FDTD),分析了在不同短截线长度和PBG结构方孔边长的情况下,该滤波器的传输特性.文中还给出了该滤波器和Rumsey方法与Kim方法设计的级联、并联两种PBG结构低通滤波器的传输特性的模拟结果及其对比分析.最后,文中给出了模拟结果和测试结果,来验证所设计的低通滤波器的有效性.     

色散媒质中ADI-FDTD

基于交替方向隐式(ADI)技术的时域有限差分(FDTD)法是一种非条件稳定的计算方法，该方法的时间步长不受Courant稳定条件限制，而由数值色散误差决定。与传统的FDTD相比，ADI-FDTD增大了时间步长，从而缩短了总的计算时间。本文采用递归卷积方法将ADI-FDTD推广应用于色散媒质，推导了二维情况下色散媒质中的ADI-FDTD迭代公式。应用推导公式计算了色散土壤中目标的散射，并与色散媒质FDTD结果对比，在大量减少计算时间的情况下，两者结果符合很好。     

一种适用于任意色散媒质的新型FDTD方法研究

本文提出一种新的适用于各种复杂色散媒质的时域有限差分法,将色散媒质表征为一组无限冲激响应滤波器(IIR),由此导出基于介电常数和导电系数的时域有限差分方程,并对算法的稳定性条件和数值色散关系进行分析.这种改进的FDTD能分析与频率有关的电磁场问题.为验证该方法的有效性和可靠性,本文用冲激响应不变法设计IIR滤波器模拟色散媒质,并对高斯脉冲入射色散媒质的情况进行数值模拟,结果与解析值完全吻合.     

色散媒质中ADI-FDTD的PML

基于交替方向隐式(ADI)技术的时域有限差分法(FDTD)是一种非条件稳定的计算方法,该方法的时间步长不受Courant稳定条件限制,而是由数值色散误差决定。与传统的FDTD相比, ADI-FDTD增大了时间步长, 从而缩短了总的计算时间。该文采用递归卷积(RC)方法导出了二维情况下色散媒质中ADI-FDTD的完全匹配层(PML)公式。应用推导公式计算了色散土壤中目标的散射,并与色散媒质中FDTD结果对比,在大量减少计算时间的情况下,两者结果符合较好。     

N阶色散媒质的FDTD法与数字信号处理技术

提出了一种新的N阶色散媒质的时域分析方法,并将其表征为一组无限冲击响应滤波器,将色散媒质在FDTD中的表述问题转化为数字滤波器(IIR)的设计问题.改进FDTD能分析处理与频率有关的电磁场问题.为验证此方法的有效性和可靠性,用此方法计算了高斯平面波脉冲入射N阶色散媒质的情况,计算结果与解析值非常吻合.     

色散媒质中采用Z变换的ADI-FDTD方法

基于Z变换方法将ADI-FDTD推广应用于色散媒质,得到了二维情况下色散媒质中的迭代差分公式,同时给出了一种采用ⅡR滤波器结构来减少存储量的方法.本文方法适合于任意M阶色散媒质,最后,给出了一个算例,数据仿真结果表明,本文的算法与传统色散媒质中的FDTD相比,在计算结果吻合的情况下,存储量相当,计算效率却更高,时间步长仅仅由计算精度来决定.     

可调带宽PBG微带线

本文提出了一种新型的50Ω光子带隙(PBG)结构微带线,该PBG结构的制作是周期地改变金属导带的宽度,同时在金属接地板上刻蚀圆孔,此种PBG结构可以获得窄的通带或宽的阻带,其微带线的通带和阻带的宽度可按照设计者的要求改变。本文设计、制造和测量了两个新型的PBG结构微带线,并通过仿真验证这种新型PBG结构的仿真结果得到了实验的验证。     

Transversely anisotropic curved optical fibers: variationalanalysis of a nonstandard eigenproblem

A novel variational functional is introduced for the analysis of curved open and closed waveguides. The theory is based on the variational principle for nonstandard eigenvalue problems. The present method is valid for the arbitrary waveguide cross section and arbitrary radius of curvature for closed waveguides; for open guides, the radius should be sufficiently large, because the method predicts the real part of the propagation constant, not the imaginary part, which gives the attenuation in curved open structures. The dielectric medium can be homogeneous or nonhomogeneous with transverse and/or longitudinal anisotropy. As an example of the method, curved isotropic and anisotropic single-mode fibers with two different kinds of anisotropy models are studied. The analysis includes field distributions, changes in the dispersion curves due to reformed geometry, and birefringence characteristics in curved anisotropic fibres     

Coupled Slots on an Anisotropic Sapphire Substrate

Two analytical approaches are presented for coupled slots on an anisotropic sapphire substrate using the network analytical methods of electromagnetic fields. One is based on the quasi-static approximation and it derives the transformation from the case with the anisotropic substrate to the case with the isotropic substrate. The other is based on the hybrid mode formulation and it gives the dispersion characteristics.     

Electromagnetic scattering by an inhomogeneous plasma anisotropic sphere of multilayers

Electromagnetic scattering by an inhomogeneous plasma anisotropic sphere is formulated and obtained, where the inhomogeneous plasma anisotropic sphere is divided into (s-1) homogeneous anisotropic spherical layers. The electromagnetic fields in the inner spherical multilayers and outer free space of the inhomogeneous plasma anisotropic spherical structure can be expanded in terms of the spherical vector wave functions in plasma anisotropic medium and in isotropic medium, respectively. By applying the continuous boundary conditions of electromagnetic fields on the spherical interfaces of the (s-1)-layered homogeneous anisotropic plasma medium, the unknown expansion coefficients of fields in the multilayered plasma spherical structure are obtained, and then the electromagnetic field distributions are calculated. Numerical results for the very general inhomogeneous plasma dielectric material sphere are given and the data in a special case are obtained using the present method and the method of moments accelerated with the conjugate-gradient fast-Fourier-transform approach and compared to each other to verify the correctness and applicability of the present analysis.     

On Radial Transmission Line Representations of Electromagnetic Fields in an Anisotropic Moving Medium

The problems of electromagnetic waves in moving isotropic or uniaxial mediums have been dealt with by numerous authors. Chawla and Unz considered the fields in a moving anisotropic plasma, and Chen and Cheng analyzed waves in an isotropic plasma in a moving dielectric medium. In this note we consider electromagnetic fields in a moving anisotropic medium and propose the network formulation of electromagnetic fields in the moving medium in the radial cylindrical coordinate. The method is an extension of the transmission line representation of electron beams on infinite magnetic fields. We can apply these results to the cases of any magnetic field intensity and, further, solve the complex problems for a stationary anisotropic plasma by a similar method.     

Analysis of multiconductor transmission lines of arbitrary crosssection in multilayered uniaxial media

A mixed-potential electric field integral equation is formulated and applied in conjunction with the method of moments to analyze a transmission-line system consisting of multiple conducting strips of arbitrary cross section embedded in a stratified medium with or without top and/or bottom ground planes. Each layer of the medium is possibly uniaxially anisotropic, with its optical axis perpendicular to the dielectric interfaces. Computed dispersion curves and modal currents are presented and, when possible, are compared with data available in the literature     

STW resonances on corrugated plates of finite thickness

Propagation of surface transverse waves on a corrugated plate has been analysed. Results are presented for both thin and thick isotropic plates, showing that the dispersion curves for the lowest mode correspond in the second case to a semi-infinite substrate. A frequency equation is developed for planar resonators based on this type of wave propagation, applicable to both isotropic and rotated Y-cut trigonal plates.     

导体球涂覆各向异性铁氧体介质电磁散射的解析解

该文用球矢量波函数对各向异性铁氧体介质涂覆导体球的电磁散射解析解开展研究。各向异性铁氧体介质中电磁场的球矢量波函数解可表示成第一、二、三、四类球矢量波函数之和。根据球Bessel函数的性质,可以得出导体球涂覆各向异性铁氧体介质的球矢量波函数解析解。应用铁氧体与自由空间分界面上电磁场切向连续和在导体球面上切向电场等于零的边界条件以及球矢量波函数切向正交性质,可分别得出铁氧体介质中电磁场和散射场的展开系数。给出了平面波入射情况下的数值计算结果。该文的结果可应用于有关微波器件、天线以及目标特征的分析和计算。     

Fabry-Perot resonators in uniaxially anisotropic media

This paper investigates the resonant modes of Fabry-Perot interferometers with end reflectors embedded in linear, homogeneous, uniaxially anisotropic media. It is shown that for almost all practical cases the resonant modes consist of transverse electric (TE) modes and transverse magnetic (TM) modes relative to the direction of the optic axis in the medium. Two distinct integral equations are derived which together with Maxwell's equations are sufficient to perform a detailed analysis of these modes. However, since the results of the analysis of Fabry-Perot resonators in isotropic regions are available and well understood, the approach of the paper is to reduce a given "anisotropic resonator" to two corresponding equivalent "isotropic resonators": one for determining the TE modes and the other for determining the TM modes. The equivalent isotropic resonator for the TE modes has the same geometry as the actual resonator in the anisotropic medium. The geometry of the equivalent isotropic resonator for the TM modes is derivable in a very simple manner from the geometry of the actual resonator in the anisotropic medium and from the specified orientation of the direction of the optic axis in the medium. The well-known results for resonators embedded in isotropic media may henceforth be applied to determine the resonant modes of the anisotropic resonator.     

A comprehensive study of numerical anisotropy and dispersion in 3-DTLM meshes

This paper presents a comprehensive analysis of the numerical anisotropy and dispersion of 3-D TLM meshes constructed using several generalized symmetrical condensed TLM nodes. The dispersion analysis is performed in isotropic lossless, isotropic lossy and anisotropic lossless media and yields a comparison of the simulation accuracy for the different TLM nodes. The effect of mesh grading on the numerical dispersion is also determined. The results compare meshes constructed with Johns' symmetrical condensed node (SCN), two hybrid symmetrical condensed nodes (HSCN) and two frequency domain symmetrical condensed nodes (FDSCN). It has been found that under certain circumstances, the time domain nodes may introduce numerical anisotropy when modelling isotropic media