Yinchao Chen

Finite-difference time-domain algorithm for solving Maxwell's equations in rotationally symmetric geometries

In this paper, an efficient finite-difference time-domain algorithm (FDTD) is presented for solving Maxwells equations with rotationally symmetric geometries. The azimuthal symmetry enables us to employ a two-dimensional (2-D) difference lattice by projecting the three-dimensional (3-D) Yee-cell in cylindrical coordinates (r, /spl phi/, z) onto the r-z plane. Extensive numerical results have been derived for various cavity structures and these results have been compared with those available in the literature. Excellent agreement has been observed for all of the cases investigated.

Finite-difference time-domain analysis of a stacked dual-frequency microstrip planar inverted-F antenna for mobile telephone handsets

We describe a stacked, dual-frequency microstrip planar inverted-F antenna (DF-PIFA) for mobile telephone handsets that can concurrently work in two frequency-bands, viz., those associated with the GSM and DCS 1800 systems operating at 0.9 GHz and 1.8 GHz, respectively. The proposed microstrip DF-PIFA is fed by a coaxial line, as opposed to two separated feed lines used in the conventional design. The design is carried out in a systematic manner and involves two steps. We begin with an initial configuration of the PIFA that is based on a standard design for a microstrip patch antenna fed by a coaxial line and is derived from an empirical approximation in conjunction with a transmission line model. Next, we employ a computer-aided design (CAD) tool, based on the nonuniform finite-difference time-domain (NU-FDTD) Maxwell solver, to optimize the performance characteristics of the DF-PIFA, including the return loss, the matching of the input impedance, and the far-field radiation patterns.

Multiple image technique (MIT) and anisotropic perfectly matched layer (APML) in implementation of MRTD scheme for boundary truncations of microwave structures

This paper presents an adjustable multiple image technique (MIT) and an anisotropic perfectly matched layer (APML) employed in the context of multiresolution time-domain (MRTD) scheme for the truncation of the computational boundary, with the MIT used for perfect electrically conducting (PEC) shields and the APML for open structures. We begin by presenting a systematic formulation for developing the constitutive relations and update equations in the transform domain of the MRTD, when considering both the original and image regions. We then illustrate the applications of the above techniques by analyzing a two-layer dielectric-loaded cavity, printed circuit enclosed by a PEC, as well as open transmission lines. Although, in principle, one can employ a large number of images to ensure the accuracy of the MRTD computation, in practice, it is useful, from the point-of-view of computational efficiency, to develop a criterion that determines the number of requisite images. While its formulation may appear to be lengthy, the MIT is based on physical concepts that are fairly well suited for computer programming.

Hybrid finite-difference/finite-volume time-domain analysis for microwave integrated circuits with curved PEC surfaces using a nonuniform rectangular grid

In this paper, we present a hybrid algorithm that combines the finite-difference time-domain (FDTD) and finite-volume time-domain (FVTD) methods to analyze microwave integrated-circuit structures that may contain curved perfect electric conductor (PEC) surfaces. We employ the conventional nonuniform FDTD in regions where the objects are describable with a rectangular mesh, while applying the FVTD method elsewhere where we need to deal with curved PEC configurations. Both the FDTD and FVTD quantities are defined in the mutually overlapping regions, and these fields from the respective regions are interpolated by using their nearest neighbors. We validate this algorithm by analyzing the scattering parameters of a stripline with one or more adjacent cylindrical vias, whose geometries are frequently encountered in printed-circuit-board designs. It is found that the hybrid FDTD-FVTD approach requires little increase in central processing unit time and memory in comparison to the conventional FDTD, while its computational accuracy is significantly improved over a wide range of frequencies. Specifically, this accuracy is found to be comparable to that achieved by doubling the mesh density of the staircased FDTD.

Microstrip resonators on anisotropic substrates

The spectral domain method is applied to study shielded microstrip resonators printed on anisotropic substrates. A Greens function that takes into account the dielectric anisotropy effects is derived through a fourth-order formulation. Galerkins method is then applied to form the characteristic equation from which the resonant frequency of the microstrip resonator is numerically obtained. Results for a microstrip situated on an isotropic substrate are used to validate the theory. >

A nonuniform FDTD technique for efficient analysis of propagation characteristics of optical-fiber waveguides

In this paper, we present a highly efficient one-dimensional cylindrical nonuniform finite-difference time-domain (1-D CNUFDTD) method, which utilizes the unsplit anisotropic perfectly matched layer (APML) for mesh truncation along the radial direction to analyze axisymmetric optical-fiber waveguides. As a first step, we validate the proposed FDTD algorithm by analyzing a uniform dielectric waveguide of circular cross section and show that the results are in excellent agreement with the conventional mode theory solutions. Next, we apply the algorithm to analyze propagation characteristics of a number of commonly used optical-fiber waveguides, i.e., step-index multimode, graded-index multimode, and single-mode step-index configurations.

An FDTD-Touchstone hybrid technique for equivalent circuit modeling of SOP electronic packages

The electromagnetic-field behavior within electronic packages used for high-speed digital-circuit or high-frequency analog-circuit applications often cannot be accurately modeled by using a quasi-static approximation, and a frequency-dependent analysis is sometimes needed for accurate modeling. In this paper, we employ the finite-difference time-domain (FDTD) approach, in conjunction with the commercially available software called Touchstone, to model the generic 24-pin silicon on plastic (SOP) package. The model for the package includes many details, such as the plastic encasement, bonding pads, and wires. The frequency responses of the package are tested against the results obtained with only the FDTD algorithm. It is shown that by extracting the equivalent-circuit elements from the field data, the hybrid FDTD-Touchstone technique allows greater flexibility in deriving a circuit configuration at the expense of fine tuning the circuit to reproduce the response of the package. It is hoped that the technique presented in this paper will lead to more accurate circuit simulations of complex packaging configurations than has been possible up to this point, by using quasi-static analyses.

Efficient and accurate finite-difference time-domain analysis of resonant structures using the Blackman–Harris window function

In this paper, we present a technique, based on the principle of the frequency-domain convolution of a time-domain signature and a truncation window function, to process the electromagnetic field solution in a resonant structure derived by using the finite-difference time-domain (FDTD) algorithm. We show that the use of this technique enables us to substantially reduce the total number of iterations provided that certain criteria are imposed on the time and frequency resolutions, as well as on the Nyquist sampling rate. The conventional approach to terminating the time iteration is to employ a rectangular windowing (RGW), which induces the unwanted Gibbs phenomenon in the frequency domain. To avoid this, we apply the Blackman–Harris window (BHW) function which modulates as well as truncates the computed time-domain electromagnetic signals. We demonstrate via a numerical experiment that the BHW modulation and truncation yield excellent results with only a small number of iterations, often only one-tenth of that needed in the RGW method.xa0© 1997 John Wiley & Sons, Inc. Microwave Opt Technol Lett 15: 389–392, 1997.

Design and analysis of a stacked dual-frequency microstrip planar inverted-F antenna for mobile telephone handsets using the FDTD

We present the design of a microstrip, dual-frequency planar inverted-F antenna (DF-PIFA) for mobile telephone handsets that can concurrently work at two frequency bands, viz., the GSM and DCS 1800 systems, which operate at 0.9 and 1.8 GHz, respectively. A computer-aided design (CAD) tool, based on the non-uniform finite difference time domain (NU-FDTD) Maxwell solver, is employed to optimize the performance characteristics of the DF-PIFA, including the return loss, impedance match, frequency bandwidth and the far-field radiation pattern.

Transformed-space non-uniform pseudo-spectral time domain (NU-PSTD) algorithm without the use of the non-uniform FFT

We present a new non-uniform pseudo-spectral time domain (NUPSTD) method for electromagnetic applications, in which we transform a non-uniform grid {x/sub i/} into a uniform one {u/sub i/} before applying the fast Fourier transform (FFT) to obtain the spatial derivatives. The transformed spatial derivatives are subsequently converted back to the real space via the use of interpolation formulas. The resultant scheme differs from the uniform PSTD algorithm only by a single factor of du/dx, and has a computational complexity of O(NlogN); hence, it preserves the efficiency of the uniform scheme. We demonstrate the application of the new method by considering the test case of a single dielectric slab. The computed results are in excellent agreement with the analytical solution up to frequencies for which the discretization size is only 3 cells per wavelength.