Finite-difference time-domain solution of Maxwell's equations forthe dispersive ionosphere

The application of the finite-difference time-domain (FDTD) technique to problems in ionospheric radio wave propagation is complicated by the dispersive nature of the ionospheric plasma. In the time domain, the electric displacement is the convolution of the dielectric tensor with the electric field, and thus requires information from the entire signal history. It is shown that this difficulty can be avoided by returning to the dynamical equations from which the dielectric tensor is derived. By integrating these differential equations simultaneously with the Maxwell equations, temporal dispersion is fully incorporated. An FDTD approach utilizing the vector wave equation is also presented. The accuracy of the method is shown by comparison for a special case for which an analytic solution is available. The method is demonstrated with examples of pulse propagation in one and two dimensions. The computational limitations of present-generation computers are discussed. The application of this approach to the study of wave propagation in randomly structured ionization is addressed     

基于FDTD的微带缝隙漏波天线分析

应用时域有限差分法(FDTD)对微带缝隙漏波天线进行分析,直观地得到了微带缝隙漏波天线内部的电场分布。提出了一条有效的经验公式,成功地计算了微带缝隙漏波天线的漏波传播系数,与实验数据吻合较好。比较了不同缝隙宽度和微带宽度对微带缝隙漏波天线性能的影响。证明了在微带漏波天线上开缝可以有效地减少天线尺寸及降低天线的工作频率。     

A semivectorial finite-difference time-domain method (optical guided structure simulation)

A semivectorial finite-difference time-domain method (FDTD) that solves the vector wave equations for the transverse electric fields is presented and validated. By taking into consideration the boundary conditions for the transverse, electric fields in the finite-difference scheme, the polarization effect of the electromagnetic waves can be modeled. In comparison with the full vector FDTD, the present approach requires less memory and is more computational efficient. The method is validated by a comparison with the exact analytical solutions as well as the full vector FDTD results and is shown to be very accurate.<>     

A new Ka-band microstrip Y-junction circulator with a ferrite sphere

A novel microstrip circulator with a magnetized ferrite sphere is proposed for millimetre wave communications. A three-dimensional finite difference time-domain (FDTD) approach for the analysis of this ferrite sphere-based microstrip circulator is presented. The electromagnetic fields inside the ferrite junction are calculated by using special updating equations derived from the equation of motion of the magnetization vector and Maxwell's curl equations in consistency. Frequency-dependent insertion loss, isolation and reflection loss of circulator are calculated over a wide band of frequencies with a single FDTD run. Experimental results at the Ka-band are presented and compared with theoretical simulation. Good agreement is found between them.     

Development of the Microstrip Circulator with a Magnetized Ferrite Sphere in Millimeter Wave Band

In this paper, a novel microstrip circulator with a magnetized ferrite sphere is proposed for various millimeter wave communications. A three-dimensional Finite-Difference Time-Domain (FDTD) approach for the analysis of this ferrite sphere based microstrip circulator is first presented. The electromagnetic fields inside the ferrite junction are calculated using special updating equations derived from the equation of motion of the magnetization vector and Maxwell's curl equations in consistency. Frequency dependent insertion loss, isolation and reflection loss of circulator are calculated over a wide band of frequencies with a single FDTD run. Experimental results at Ka band are presented and compared with theoretical simulations. As a result, a good agreement is found between them.     

Application of the FD-TD method to the analysis of circuitsdescribed by the two-dimensional vector wave equation

A class of microwave circuits described by a two-dimensional vector wave equation is defined. It is proposed to refer to them as vector two-dimensional or 2-DV circuits to distinguish them from circuits described by a two-dimensional scalar wave equation (typically referred to as 2-D circuits). It is shown that the 2-DV class contains some planar circuits filled with anisotropic media, two-dimensional waveguide discontinuities, and circular waveguide discontinuities. Calculation of dispersion characteristics of inhomogeneously filled hollow waveguides is an eigenvalue problem belonging to the 2-DV class. Application to the finite-difference-time-domain (FDTD) method to the analysis of 2-DV circuits is described. Examples show the efficiency of the method for several types of circuit     

A hybrid implicit-explicit FDTD scheme for nonlinear opticalwaveguide modeling

A hybrid implicit-explicit finite-difference time-domain (FDTD) method for solving the wave equation in nonlinear optical waveguiding structures is proposed. The new scheme combines the computational simplicity of the explicit scheme in linear medium regions with the superior stability property of the partially implicit scheme in regions of nonlinear materials, thus eliminating potential problems of instability associated with nonlinearity. Simulation results for Kerr-type nonlinear slab waveguides and corrugated waveguides are presented and compared with those obtained using the conventional noniterative FDTD scheme     

基于FDTD的薄膜体声波谐振器的数值分析

提出了基于时域有限差分方法对薄膜体声波谐振器进行数值分析的新方法.利用时域有限差分法理论对压电材料的控制方程和牛顿方程在空间和时间上进行了离散化,通过得到的差分方程直接得出了声场传播的时域数值解.使用该数值方法对薄膜体声波谐振器的电学特性阻抗进行了分析,并将结果与一维Mason模型的解析解进行了比较验证.     

Finite-difference approach to the solution of time-domain integralequations for layered structures

A numerical algorithm for the analysis of transient electromagnetic fields in planar structures is proposed based on the time-domain magnetic-field integral equation (MFIE), electric-field integral equation (EFIE), and the marching-on-in-time approach. The field vectors are represented in terms of vector potential functions which are calculated either by integration or by the three-dimensional (3-D) wave equation according to the geometry of the structure. Thus, the algorithm combines the advantages of integral equation techniques and finite-difference schemes. While this approach is applicable to any geometries, it is especially suitable for multilayered planar structures and is competitive to the finite-difference time-domain (FDTD) method in the case of open and radiating problems. Theoretical results are verified by the analysis of a pulse propagation in a homogeneous open-end microstrip line     

Stability criterion for radial wave equation in finite-differencetime-domain method

A relaxed time-step stability criterion is derived for the radial wave equation in Schelkunoff form approximated by a finite-difference time-domain (FDTD) method. The criterion is established by comparing with the Cartesian Laplacian operator. This is the first step in developing stability analysis for a spherical wave implementation in FDTD     

等离子体与电磁波相互作用FDTD 数值模拟

围绕等离子体与电磁波相互作用的问题,将气体分子动力学与电磁场理论相结合,基于玻尔兹曼方程和麦克斯韦方程建立了等离子体与电磁波相互作用自洽模型,为了对模型进行验证,将该方法与经典的电流密度卷积时域有限差分法进行对比,以一维情况下电磁波由自由空间向等离子体内传播为例,应用时域有限差分法对二者进行了数值仿真,仿真结果证明了所建立模型的正确性。此外,基于该模型仿真分析了等离子体参数对电磁波在等离子体中传播的影响,为等离子体与电磁波相互作用的研究提供了一种新思路和新方法。     

网格长度对FDTD计算的影响

基于平面波传播的物理性质，提出一种FDTD改进方法——在研究稳态问题时，为保证数字波前与入射方向垂直，网格划分不能是固定的，其长度之比应随人射方向变化。研究了改进方法对数值色散的影响，并与传统方法作了比较。在三维Yee网格中对平面波的模拟结果表明，改进方法的收敛性能大为提高，对远场散射的误差影响小。     

并行FDTD-UTD方法分析机载相控阵天线

利用时域有限差分法(FDTD)-UTD(一致性几何绕射理论)混和算法分析机载相控阵天线的辐射方向图.将复矢量场作为FDTD方法和UTD方法的接口,提出FDTD-UTD混和算法解决机载相控阵天线辐射问题.首先利用并行FDTD方法通过全波分析得到精确的相控阵的辐射复矢量场,然后将此结果作为源代入UTD算法来预测相控阵受机体的影响.结果表明该方法可以有效地解决机裁相控阵辐射分析问题.     

A New FDTD Formulation for Wave Propagation in Biological Media With Cole–Cole Model

The finite-difference time-domain (FDTD) method has been widely used to simulate the electromagnetic wave propagation in biological tissues. The Cole-Cole model is a formulation which can describe many types of biological tissues accurately over a very wide frequency band. However, the implementation of the Cole-Cole model using the FDTD method is difficult because of the fractional order differentiators in the model. In this letter, a new FDTD formulation is presented for the modeling of electromagnetic wave propagation in dispersive biological tissues with the Cole-Cole model. The Z-transform is used to represent the frequency dependent dielectric properties. The fractional order differentiators in the Cole-Cole model is approximated by a polynomial. The coefficients of the polynomial are found using a least-squares fitting method     

三维FDTD中TF/SF边界的时域群速补偿法

TF／SF（Total Field／Scattered Field）法是FDTD（Finite-Difference Time—Domain）数值算法中引入平面波源的有效方法之一。本文对TF／SF法中的一维辅助渡源法进行改进，首先推导出三维FDTD网格内的电磁波传播群速和相速的近似解析解。为预测离散网格内电磁波传播提供理论基础；然后以此为依据，提出对一维辅助波源的时域群速补偿法。经过实际三维FDTD问题的数值模拟，证实了本文方法在保持一维辅助波源法高效简洁的同时，进一步减少了泄露误差，给FDTD计算散射问题提供了有力工具。     

Envelope LOD Wave Equation PML Algorithm for Dispersive Band-Limited FDTD Applications

Unconditionally stable envelope scalar wave equation perfectly matched layer algorithm is presented for truncating dispersive finite difference time domain (FDTD) grids. The algorithm is based on the locally one dimensional FDTD formulations and it is suitable for band-limited electromagnetic applications. Two-dimensional numerical examples are included to show the validity of the proposed formulations.     

有限口径亚波长衍射光学器件的严格矢量分析

利用二维时域有限差分(FDTD)方法作为严格电磁计算模式,分析、比较了连续面型和经过Farn方法得到的亚波长结构面型的衍射微柱透镜在TE极化波和TM极化波入射情况下的聚焦特性。对不同F数衍射微柱透镜的严格矢量分析表明,亚波长结构器件的聚焦特性对输入光波的极化情况有更强的敏感性。并简要讨论了FDTD方法的数值色散和计算空间吸收边界的设置等问题。     

机载短波天线间隔离度的全波分析

对飞机等复杂形体及机载短波天线进行全波ＦＤＴＤ数值模拟所需的数学建模方法的介绍,研究了机载短波天线间隔离度的分析计算方法,并以波音７０７－３２０Ｂ飞机为例计算了机上４付短波天线间隔离度。所用方法及所得结果可作为飞机电磁兼容分析与设计的手段和依据。     

时域有限差分法中金属薄板边缘场差分方程的修正

本文提出了一种时域有限差分法中金属薄板边缘场修正的差分方程.以带状线和V形天线为例检验了修正的差分方程的有效性,数值结果表明,和金属板边缘阶梯近似相比,计算精度大大提高.     

一种新的FDTD入射场设置方法

本文提出了一种新的入射场设置方法.采用一维FDTD算法来模拟入射波.所得结果与通常的入射场解析表达式的结果比较表明,采用一维FDTD算法引入的入射波在总场区分布均匀,在散射场区泄漏小.