同轴馈电耦合微带天线的MPSTD-FDTD分析

将多区域时域伪谱(MPSTD)与时域有限差分(FDTD)相结合的混合算法应用于同轴馈电耦合微带天线的分析,该混合算法充分发挥两种时域算法的优越性,对同轴馈电耦合微带天线进行了准确建模与快速分析,数值仿真验证了该算法的有效性和准确性。     

Application of the three-dimensional finite-difference time-domainmethod to the analysis of planar microstrip circuits

A direct three-dimensional finite-difference time-domain (FDTD) method is applied to the full-wave analysis of various microstrip structures. The method is shown to be an efficient tool for modeling complicated microstrip circuit components and microstrip antennas. From the time-domain results the input impedance of a line-fed rectangular patch antenna and the frequency-dependent scattering parameters of a low-pass filter and a branch-line coupler are calculated. These circuits were fabricated and the measurements made on them are compared with the FDTD results and shown to be in good agreement     

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 fully three-dimensional simulation of a ground-penetrating radar:FDTD theory compared with experiment

A fully three-dimensional, finite-difference time-domain (FDTD) model of a ground-penetrating radar is described. The FDTD simulation completely models the transmitting and receiving antennas, the antenna feeds, the dispersive Earth, and the buried object. Results of scattering from three different buried cylindrical pipes are compared to previously measured results for a one-third size scale model of an actual radar and are shown to be in good agreement     

FDTD analysis of electromagnetic wave radiation from systemscontaining horn antennas

The application of the finite-difference time-domain (FDTD) method to various radiating structures is considered. These structures include two- and three-dimensional waveguides, flared horns, a two-dimensional parabolic reflector, and a two-dimensional hyperthermia application. Numerical results for the horns, waveguides, and parabolic reflectors are compared with results from using the method of moments (MM). The results for the hyperthermia application are shown as extensions of the previously validated models. This new application of the FDTD method is shown to be useful when other numerical or analytic methods cannot be applied     

Numerical stability of nonorthogonal FDTD methods

In this paper, a sufficient test for the numerical stability of generalized grid finite-difference time-domain (FDTD) schemes is presented. It is shown that the projection operators of such schemes must be symmetric positive definite. Without this property, such schemes can exhibit late-time instabilities. The origin and the characteristics of these late-time instabilities are also uncovered. Based on this study, nonorthogonal grid FDTD schemes (NFDTD) and the generalized Yee (GY) methods are proposed that are numerically stable in the late time for quadrilateral prism elements, allowing these methods to be extended to problems requiring very long-time simulations. The study of numerical stability that is presented is very general and can be applied to most solutions of Maxwell's equations based on explicit time-domain schemes     

Higher-order finite-difference schemes for electromagneticradiation, scattering, and penetration .1. Theory

Higher-order schemes for the finite-difference time-domain (FDTD) method are presented, in particular, a second-order-in-time, fourth-order-in-space method: FDTD(2,4). This method is compared to the original Yee (1966) FDTD scheme. One-dimensional update equations are presented, and the characteristics of the FDTD(2,4) scheme are investigated. Theoretical results for numerical stability and dispersion are presented, with numerical results for the latter, as well. The use of the perfectly matched layer for the FDTD(2,4) scheme is discussed, and numerical results are shown     

A finite-difference time-domain near zone to far zonetransformation [electromagnetic scattering]

An efficient time-domain near-zone-to-far-zone transformation for FDTD (finite-difference-time-domain) computations is presented. The approach is to keep a running accumulation of the far-zone time-domain vector potentials due to the tangential electric and magnetic fields on a closed surface surrounding the scatterer at each time step. At the end of the computation, these vector potentials are converted to time-domain far-zone fields. Many far-zone bistatic directions can be included efficiently during one FDTD computational run. Frequency domain results can be obtained via fast Fourier transform. Wideband results for scattering from a perfectly conducting plate were obtained from a single FDTD computation transformed to the frequency domain, and compared with moment method results. This approach is significantly more efficient than computing many FDTD results using sinusoidally varying excitation if a wide frequency band is of interest. Coupled with recent advances in computing FDTD results for frequency-dependent materials, wideband results for far-zone scattering from targets including frequency-dependent materials can be obtained efficiently     

Incorporating two-port networks with S-parameters into FDTD

A modeling approach for incorporating a two-port network with S-parameters in the finite-difference time-domain (FDTD) method is reported. The proposed method utilizes the time-domain Y-parameters to describe the network characteristics, and incorporates the Y-parameters into the FDTD algorithm. The generalized pencil-of-function technique is applied to improve the memory efficiency of this algorithm by generating a complex exponential series for the Y-parameters and using recursive convolution in the FDTD updating equations. A modeling example is given, which shows that this approach is effective and accurate. This modeling technique can be extended for incorporating any number of N-port networks in the FDTD modeling     

A new FDTD algorithm based on alternating-direction implicit method

In this paper, a new finite-difference time-domain (FDTD) algorithm is proposed in order to eliminate the Courant-Friedrich-Levy (CFL) condition restraint. The new algorithm is based on an alternating-direction implicit method. It is shown that the new algorithm is quite stable both analytically and numerically even when the CFL condition is not satisfied. Therefore, if the minimum cell size in the computational domain is required to be much smaller than the wavelength, this new algorithm is more efficient than conventional FDTD schemes in terms of computer resources such as central-processing-unit time. Numerical formulations are presented and simulation results are compared to those using the conventional FDTD method     

Analysis of shielded membrane microstrip line using the finite-difference time-domain method

A simple and efficient analysis method of the shielded membrane microstrip (SMM) line using the finite-difference time-domain (FDTD) method is presented. New FDTD equations are derived using the contour path FDTD concept for the Yee cell which contains three thin dielectric sheets of membrane. The characteristic impedance and the effective dielectric constant of the SMM line are calculated using our proposed method. The method is validated by comparison with the results shown by Robertson et al. [1996].     

Z-transform theory and the FDTD method

In implementing the finite-difference time-domain (FDTD) method on materials which are dispersive or nonlinear, the relationship between the flux density and the electric field can be the most complicated part of the problem. Because the FDTD method is a sampled time-domain method, this relationship can be can be looked upon as a digital filtering problem. The Z transform is typically used in digital filtering and signal processing problems. The paper illustrates the use of the Z transform in implementing the FDTD method where complicated dispersive or nonlinear materials are involved     

Dispersion compensation for Huygens' sources and far-zonetransformation in FDTD

The equivalence principle is utilized for generation of both incident plane waves and for near- to far-zone transformation in the finite-difference time-domain (FDTD) method. Small errors will appear due to numerical dispersion when a plane wave is generated by Huygens' sources using an analytical expression for the incident field. These errors can be derived from the numerical dispersion relation in the frequency domain. By using a second-order approximation of the numerical wavenumber it is shown that a simple approximative time-domain compensation procedure for the dispersion can be derived. This has been implemented in a Huygens' source routine and in a time-domain near- to far-zone transformation routine. It is shown that this compensation significantly reduces the errors produced when calculating far-zone scattered fields of low amplitude. It is also shown that it is sufficient to compensate either the Huygens' sources or the time-domain near- to far-zone transformation with respect to dispersion. For validation, plane wave propagation through empty space and scattering of a dipole have been studied     

Analyzing the stability of the FDTD technique by combining the vonNeumann method with the Routh-Hurwitz criterion

This paper addresses the problem of stability analysis of finite-difference time-domain (FDTD) approximations for Maxwell's equations. The combination of the von Neumann method with the Routh-Hurwitz criterion is proposed as an algebraic procedure for obtaining analytical closed-form stability expressions. This technique is applied to the problem of determining the stability conditions of an extension of the FDTD method to incorporate dispersive media previously reported in the literature. Both Debye and Lorentz dispersive media are considered. It is shown that, for the former case, the stability limit of the conventional FDTD method is preserved. However, for the latter case, a more restrictive stability limit is obtained. To overcome this drawback, a new scheme is presented, which allows the stability limit of the conventional FDTD method to be maintained     

Finite-difference, time-domain analysis of lossy transmission lines

An active and efficient method of including frequency-dependent conductor losses into the time-domain solution of the multiconductor transmission line equations is presented. It is shown that the usual A+B√s representation of these frequency-dependent losses is not valid for some practical geometries. The reason for this the representation of the internal inductance the at lower frequencies. A computationally efficient method for improving this representation in the finite-difference time-domain (FDTD) solution method is given and is verified using the conventional time-domain to frequency-domain (TDFD) solution technique     

A 3-D precise integration time-domain method without the restraints of the courant-friedrich-levy stability condition for the numerical solution of Maxwell's equations

In this paper, a new three-dimensional time-domain method for solving vector Maxwell's equations, called the precise-integration time-domain (PITD) algorithm, is proposed in order to eliminate the Courant-Friedrich-Levy (CFL) condition restraint. The new algorithm is based on the precise-integration technique. It is shown that this method is quite stable even when the CFL condition is not satisfied. Although the memory requirement of the PITD method is much larger than that of the finite-difference time-domain (FDTD) method, this new algorithm is very appealing since the time step used in the simulation is no longer restricted by stability. As a result, computation speed can be improved. Therefore, if the minimum cell size in the computational domain is required to be much smaller than the wavelength, this new algorithm is more efficient than the FDTD scheme. Theoretical proof of the unconditional stability is shown and numerical results are presented to demonstrate the effectiveness and efficiency of the method. It is found that the accuracy of the PITD is independent of the time-step size.     

Application of Haar-wavelet-based multiresolution time-domainschemes to electromagnetic scattering problems

The multiresolution time-domain (MRTD) algorithm is applied to the problem of general two-dimensional electromagnetic scattering. A Haar wavelet expansion is utilized. A parallel between Haar MRTD and the classic Yee finite-difference time-domain (FDTD) algorithm is discussed, and results of simulations on canonical targets are shown for comparison. We focus on the incident-field implementation, which, in our case, consists of a pulsed plane wave. Also, we consider scattering in a half-space environment, with application to subsurface sensing. The results illustrate the advantage of the Haar MRTD method as compared with the classic FDTD, which consists of reduced memory and execution time requirements, without sacrificing accuracy     

Thin-Wire Model Using Subcellular Extensions in the Finite-Difference Time-Domain Analysis of Thin and Lossy Insulated Cylindrical Structures in Lossy Media

Recently, a subcellular thin-wire model for the finite-difference time-domain (FDTD) simulation of resistively coated cylinders with lossless insulating and surrounding media was presented. In this paper, it is shown that this model can be extended to lossy cases. The material discontinuity between lossy insulating and surrounding media is corrected as the time-domain boundary condition. The convolution term of the boundary condition is solved by employing a recursive technique. Applying the contour-path integration to the FDTD unit cells around the wire, one may find the coarse-grid-based equation with the correction term and factors for the material discontinuity and the quasi-static field behavior around the wire. In the 2-D cylindrical coordinates with rotational symmetry, the validity of the proposed model is confirmed by an impedance analysis of insulated and resistive antennas according to the electrical properties of insulating and surrounding media, as well as the choice of cell size.      

Signal integrity analysis of interconnects using the FDTD methodand a layer peeling technique

This paper presents the application of an impedance layer peeling technique to network parameter extraction from finite-difference time-domain (FDTD) simulations. It is shown that the combination of both methods offers a simple and efficient way to analyze lossless linear 1- or 2-port structures. The extraction of equivalent entirely in the time domain and the optimization of lumped element parameters is not necessary. Special attention is paid to the problem of injecting voltage steps with short risetimes into the FDTD grid. Results obtained with this technique are compared to network analyzer measurements and usual FDTD analysis based on scattering parameter extraction     

A FDTD-based modal PML

The finite-difference time-domain (FDTD) method is one of the most popular numerical methods for solving electromagnetic problems because of its algorithmic simplicity and flexibility. For an open waveguide structure, modal perfectly matched layer (PML) schemes have been developed as efficient absorbing terminations. However, since these PML schemes are not derived directly from the FDTD algorithm, they do not perform as well as the original three-dimensional (3-D) PMLs. In this letter, a FDTD-based one-dimensional modal PML is proposed. Because it is derived directly from the FDTD formulation, its numerical dispersion characteristics are very close to the original FDTD method. Relative differences between results obtained with the proposed method and the original 3-D PML are found to be less than -220dB, and the proposed modal PML is shown to perform at least the same as the original PML if not better.