A Robust Approach for the Derivation of Closed-form Green's Functions

Cataloged from PDF version of article.Spatial-domain Green’s functions for multilayer, planar geometries are cast into closed forms with two-level approximation of the spectral-domain representation of the Green’s functions. This approach is very robust and much faster compared to the original one-level approximation. Moreover, il does not require the investigation of the spectral-domain behavior of the Green’s functions in advance to decide on the parameters of the approximation technique, and it can be applied to any component of the dyadic Green’s function with the same ease

Closed form Greens functions for general sources and stratified media

Cataloged from PDF version of article.The closed-form Green's functions of the vector and scalar potentials in the spatial domain are presented for the sources of horizontal electric, magnetic, and vertical electric, magnetic dipoles embedded in general, multilayer, planar media. First, the spectral domain Green's functions in an arbitrary layer are derived analytically from the Green's functions in the source layer by using a recursive algorithm. Then, the spatial domain Green's functions are obtained by adding the contributions of the direct terms, surface waves, and complex images approximated by the Generalized Pencil of Functions Method (GPOF). In the derivations, the main emphasis is to put these closed-form representations in a suitable form for the solution of the mixed potential integral equation (MPIE) by the method of moments in a general three-dimensional geometry. The contributions of this paper are: 1) providing the complete set of closed-form Green's functions in spectral and spatial domains for general stratified media; 2) using the GPOF method, which is more robust and less noise sensitive, in the derivation of the closed-form spatial domain Green's functions; and 3) casting the closed-form Green's functions in a form to provide efficient applications of the method of moments. © 1995 IEE

Spurious radiation from microstrip interconnects

Cataloged from PDF version of article.The level of spurious radiation from microstrip interconnects, which are modeled here as either single or asymmetric parallel microstrip lines terminated by arbitrary complex load impedances, is investigated in this paper. The calculation of the spurious radiation requires a knowledge of the current distributions on the microstrip lines, and the first step is to compute these distributions efficiently. This is carried out here by using the method of moments in conjunction with closedform spatial domain Green’s functions that circumvent the need for time-consuming evaluation of Sommerfeld integrals. Once the current distributions on the etches have been obtained, the level of spurious radiation, which is defined as the radiated power crossing the plane parallel to the plane of interconnects, is calculated. The dependence of the spurious radiation on the lengths of the lines and on the termination impedances of the etches is also studie

Electromagnetic scattering solution of conducting strips in layered media using the fast multipole method

Cataloged from PDF version of article.The fast multipole method (FMM) is applied to the solution of the electromagnetic scattering problems in layered media for the first time. This is achieved by using closedform expressions for the spatial-domain Green’s functions for layered media. Until now, the FMM has been limited to the homogeneous-medium problems. An integral equation based on the two-dimensional scalar Helmholtz equation is solved to compute the electromagnetic scattering from sample geometries of conducting strips in layered media in order to demonstrate the accuracy and the efficiency of the new method

Numerically Efficient Analysis of Planar Microstrip Configurations Using Closed-Form Green's Functions

Cataloged from PDF version of article.An efficient technique for the analysis of a general class of microstrip structures with a substrate and a superstrate is investigated in this paper using newly-derived closed-form spatial domain Green's functions employed in conjunction with the Method of Moments (MoM). The computed current distributions on the microstrip structure are used to determine the scattering parameters of microstrip discontinuities and the input impedances of microstrip patch antennas. It is shown that the use of the closed-form Green's functions in the context of the MoM provides II computational advantage in terms of the CPU time by almost two orders of magnitude over the conventional spectral domain approach employing the transformed version of the Green's functions

An efficient method for electromagnetic characterization of 2-D geometries in stratified media

Cataloged from PDF version of article.A numerically efficient technique, based on the spectral-domain method of moments (MoM) in conjunction with the generalized pencil-of-functions (GPOF) method, is developed for the characterization of two-dimensional geometries in multilayer planar media. This approach provides an analytic expression for all the entries of the MoM matrix, explicitly including the indexes of the basis and testing functions provided that the Galerkin’s MoM is employed. This feature facilitates an efficient modification of the geometry without the necessity of recalculating the additional elements in the MoM matrix. To assess the efficiency of the approach, the results and the matrix fill times are compared to those obtained with two other efficient methods, namely, the spatial-domain MoM in conjunction with the closed-form Green’s functions, and a fast Fourier transform algorithm to evaluate the MoM matrix entries. Among these, the spectral-domain MoM using the GPOF algorithm is the most efficient approach for printed multilayer geometries

A numerically efficient technique for the analysis of slots in multilayer media

Cataloged from PDF version of article.A numerically efficient technique for the analysis of slot geometries in multilayer media is presented using closed-form Green's functions in spatial domain in conjunction with the method of moments (MoM). The slot is represented by an equivalent magnetic-current distribution, which is then used to determine the total power crossing through the slot and the input impedance. In order to calculate power and current distribution, spatial domain closed form Green's functions are expanded as power series of the radial distance rho, which makes the analytical evaluation of the spatial domain integrals possible, saving a considerable amount of computation time

Use of computationally efficient method of moments in the optimization of printed antennas

Cataloged from PDF version of article.Derivation of the closed-form Green’s functions and analytical evaluation of the method of moments (MOM) matrix entries have improved the computational efficiency of the significantly in the analysis of printed geometries. With this background in mind, an extension of this efficient numerical technique is to incorporate an optimization algorithm and to assess its potential as a computer-aided design (CAD) tool. Therefore, we have employed the Gradient search and Genetic algorithms, in conjunction with the electromagnetic (EM) simulation technique, to a number of representative examples of interest

Design of dual-frequency probe-fed microstrip antennas with genetic optimization algorithm

Cataloged from PDF version of article.Dual-frequency operation of antennas has become a necessity for many applications in recent wireless communication systems, such as GPS, GSM services operating at two different frequency bands, and services of PCS and IMT-2000 applications. Although there are various techniques to achieve dual-band operation from various types of microstrip antennas, there is no efficient design tool that has been incorporated with a suitable optimization algorithm. In this paper, the cavity-model based simulation tool along with the genetic optimization algorithm is presented for the design of dual-band microstrip antennas, using multiple slots in the patch or multiple shorting strips between the patch and the ground plane. Since this approach is based on the cavity model, the multiport approach is efficiently employed to analyze the effects of the slots and shorting strips on the input impedance. Then, the optimization of the positions of slots and shorting strips is performed via a genetic optimization algorithm, to achieve an acceptable antenna operation over the desired frequency bands. The antennas designed by this efficient design procedure were realized experimentally, and the results are compared. In addition, these results are also compared to the results obtained by the commercial electromagnetic simulation tool, the FEM-based software HFSS by ANSOFT

Analytical Evaluation of the MoM Matrix Elements

Cataloged from PDF version of article.Derivation of the closed-form Green’s functions has eliminated the computationally expensive evaluation of the Sommerfeld integrals to obtain the Green’s functions in the spatial domain. Therefore, using the closed-form Green’s functions in conjunction with the method of moments (MOM) has improved the computational efficiency of the technique significantly. Further improvement can he achieved on the calculation of the matrix elements involved in the MOM, usually double integrals for planar geometries, by eliminating the numerical integration. The contribution of this paper is to present the analytical evaluation of the matrix elements when the closed-form Green’s functions are used, and to demonstrate the amount of improvement in computation time