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Title: MODEL-BASED PARAMETER ESTIMATION IN ELECTROMAGNETICS: III--Applications to EM Integral Equations
Abstract: Problem solving in electromagnetics, whether by analysis, measurement or computation, involves not only activities specific to these particular categories, but also some concepts that are common to all. Fields and sources are sampled as a function of time, frequency, space, angle, etc. and boundary conditions are satisfied through mathematical imposition or experimental conditions. The source samples, usually the unknowns in a problem, are found numerically or analytically by requiring them to satisfy both the appropriate form of Maxwell's Equations as relationships between them, together with the applicable boundary conditions. Alternatively, source samples may be measured under prescribed experimental conditions. These sampled relationships can be interpreted from the viewpoint of signal and information processing, and are mathematically similar to various kinds of filtering operations. It is this similarity that is discussed here in the context of modelbased parameter estimation, where the dependence of electromagnetic fields and sources that produce them are both regarded as generalized signals. MBPE substitutes the requirement of obtaining all samples of desired quantities (physical observables such as impedance, gain, RCS, etc. or numerical observables such as impedance-matrix coefficients, geometrical-diffraction coefficients, etc.) from first-principles models (FPMs) or from measured data (MD) by instead using a reduced-order, physically-based approximation, a fitting model (FM), to interpolate between, or extrapolate from, FPM or MD samples. When used for electromagnetic observables, MBPE can reduce the number of samples that are required to represent responses of interest, thus increasing the efficiency of obtaining them. When used in connection with the FPM itself, MBPE can decrease the computational cost of its implementation. Some specific possibilities for improving FPM efficiency are surveyed, specifically in terms of using FMs to simplify frequency and spatial variations associated with FPMs. Examples of MBPE applications are included here as well as speculative possibilities for their further development in improving FPM performance. [Vol. 10, No. 3 (1995), Special Issue on Advances in the Application of Method of Moments to Electromagnetic Radiation and Scattering Problems, pp 9-29]
Author(s): E. K. Miller
File Type: Journal Paper
Issue:Volume: 10      Number: 3      Year: 1995
Download Link:Click here to download PDF     File Size: 2214 KB

Title: AN EXAMINATION OF THE EFFECT OF MECHANICAL DEFORMATION ON THE INPUT IMPEDANCE OF HF LPDA'S USING MBPE
Abstract: This article examines the application of Model Based Parameter Estimation (MBPE) to the evaluation of the input impedance of HF Log Periodic Dipole Arrays (LPDA) during mechanical deformation. A study of cases of lengthening, shortening and displacing one element as well as the effect of mechanical sagging of the array is made. It is found that MBPE is a useful tool for minimizing computations and/or measurements in the study of mechanical deformation. [Vol. 10, No. 3 (1995), Special Issue on Advances in the Application of Method of Moments to Electromagnetic Radiation and Scattering Problems, pp 30-37]
Author(s): J. Tobias de Beer, Duncan C. Baker
File Type: Journal Paper
Issue:Volume: 10      Number: 3      Year: 1995
Download Link:Click here to download PDF     File Size: 629 KB

Title: CURRENT-BASED HYBRID MOMENT METHOD ANALYSIS OF ELECTROMAGNETIC RADIATION AND SCATTERING PROBLEMS
Abstract: A current-based hybrid method combining the method of moments (MM) with asymptotic current expansions for the higher frequency range is presented for the analysis of arbitrarily shaped, three-dimensional, perfectly conducting electromagnetic radiation and scattering problems. Some examples demonstrate the drastic saving in memory requirement and CPU-time when applying the hybrid method as compared to the conventional MM. Even though the proposed method is a frequency domain formulation, some time domain results based on a Fourier transform are presented as they show an accurate description of diffracted and creeping waves. [Vol. 10, No. 3 (1995), Special Issue on Advances in the Application of Method of Moments to Electromagnetic Radiation and Scattering Problems, pp 38-46
Author(s): Ulrich Jakobus, Friedrich M. Landstorfer
File Type: Journal Paper
Issue:Volume: 10      Number: 3      Year: 1995
Download Link:Click here to download PDF     File Size: 739 KB

Title: HYBRID METHOD OF MOMENTS SOLUTION FOR A PERTURBED DIELECTRIC CIRCULAR CYLINDER
Abstract: A hybrid technique is developed? using the integral equation/moment method solution approach with non-free space Green's functions, for a class of scat- tering problems involving nearly-circular 2-D dielectric cylinders under TMz illumination. The technique is applicable to other nearly-canonical 2-D penetrable scatterers, and may be extended to certain 3-D geometries. Applications to several 2-D geometries are demonstrated, with scattering pre- dictions compared to those from a standard moment method code. [Vol. 10, No. 3 (1995), Special Issue on Advances in the Application of Method of Moments to Electromagnetic Radiation and Scattering Problems, pp 47-52
Author(s): William D. Wood, Jr.
File Type: Journal Paper
Issue:Volume: 10      Number: 3      Year: 1995
Download Link:Click here to download PDF     File Size: 407 KB

Title: A LOW-FREQUENCY FORMULATION OF THE METHOD OF MOMENTS VIA SURFACE CHARGES
Abstract: In this paper a formulation of the method of moments for the analysis of low frequency problems is presented. In the considered frequency range, the integral solution of Maxwell equations in terms of magnetic vector potential and electric scalar potential respectively function of currents and charges is obtained imposing the Coulomb gauge. By combining Gauss law and current continuity at the boundaries among regions with different conductivity a first set of equations is obtained. Writing Ohm's law inside the conductive regions another integral equation set that allows the determination of the conduction current and surface charges unknowns is obtained. The method of moments is then applied to this system of equations. The use of pulse functions as subsectional bases allows a quick matrix set up especially when regular volume shapes are selected. Calculated results are compared with results obtained with other methods relating to benchmark problems. [Vol. 10, No. 3 (1995), Special Issue on Advances in the Application of Method of Moments to Electromagnetic Radiation and Scattering Problems, pp 53-57]
Author(s): Nunzio Esposito, Antonino Musolino, Marco Raugi
File Type: Journal Paper
Issue:Volume: 10      Number: 3      Year: 1995
Download Link:Click here to download PDF     File Size: 332 KB

Title: A STUDY OF A RECENT, MOMENT-METHOD ALGORITHM THAT IS ACCURATE TO VERY LOW FREQUENCIES
Abstract: We give an alternative description of a recently published moment-method algorithm, which uses divergence-free and rotation-free basis functions to maintain accuracy down to very low frequencies. The basic algorithm is restricted to simply-connected and non-self-intersecting surfaces. But this restriction has little practical impact--we show how multiply-connected surfaces, self-intersecting surfaces, and one-sided surfaces can easily be converted to the required topology without changing the solution. We examine a claim that the impedance matrix is diagonally dominant, which implies a guaranteed-to-converge Jacobi type of iterative solution of the matrix equation. Finally, we show how to control catastrophic-cancellation errors that occasionally appear in the voltage vector. [Vol. 10, No. 3 (1995), Special Issue on Advances in the Application of Method of Moments to Electromagnetic Radiation and Scattering Problems, pp 58-68]
Author(s): M. Burton, S. Kashyap
File Type: Journal Paper
Issue:Volume: 10      Number: 3      Year: 1995
Download Link:Click here to download PDF     File Size: 795 KB

Title: A STUDY OF TWO NUMERICAL SOLUTION PROCEDURES FOR THE ELECTRIC FIELD INTEGRAL EQUATION AT LOW FREQUENCY
Abstract: The numerical solution of the Electric Field Integral Equation (EFIE) using two different lowfrequency formulations is investigated. The two procedures are implemented for the triangular patch modeling procedure and results obtained for both methods are compared with the original triangular patch EFIE solution. The comparisons are made on the basis of the computed current values and the inverse condition number of the moment matrix. It is observed that the condition number of the matrix can be significantly different between the two low frequency formulations and that the method used to evaluate the forcing function can affect the results both in the low and high frequency ranges. [Vol. 10, No. 3 (1995), Special Issue on Advances in the Application of Method of Moments to Electromagnetic Radiation and Scattering Problems, pp 69-80]
Author(s): Wen-Liang Wu, Allen W. Glisson, Darko Kajfez
File Type: Journal Paper
Issue:Volume: 10      Number: 3      Year: 1995
Download Link:Click here to download PDF     File Size: 841 KB

Title: ELECTROMAGNETIC SCATTERING FROM TWO DIMENSIONAL ANISOTROPIC IMPEDANCE OBJECTS UNDER OBLIQUE PLANE WAVE INCIDENCE
Abstract: The surface integral equations of a two dimensional (2D) anisotropic impedance object is formulated to obtain the electromagnetic scattered fields due to oblique plane wave incidence. The surface impedance is anisotropic with arbitrary principle directions. The moment method with pulse basis functions and point matching is used to reduce the surface integral equations to a matrix equation. Four different formulations are generated for the problem. The surface current distributions and the scattered farfields are verified against the analytical series solutions of circular impedance cylinders. Very good agreement between the numerical and the analytical solutions is obtained. A rectangular cylinder made of four soft surfaces is analyzed for oblique incidence to verify that the results behave as expected. The computer code is also verified by comparing the solutions of the different formulations against each other. [Vol. 10, No. 3 (1995), Special Issue on Advances in the Application of Method of Moments to Electromagnetic Radiation and Scattering Problems, pp 81-92]
Author(s): Ahmed A. Kishk, Per-Simon Kildal
File Type: Journal Paper
Issue:Volume: 10      Number: 3      Year: 1995
Download Link:Click here to download PDF     File Size: 1148 KB

Title: ELECTROMAGNETIC SCATTERING BY AN ARBITRARILY SHAPED SURFACE WITH AN ANISOTROPIC IMPEDANCE BOUNDARY CONDITION
Abstract: The problem of electromagnetic scattering from arbitrarily shaped, imperfectly conducting surfaces that can be represented by an anisotropic impedance boundary condition is solved numerically using the electric field integral equation and a triangular patch model for the surface. The anisotropic impedance boundary condition function is described by a constant surface dyadic within each triangular face. The procedure is validated by comparison of numerical results obtained with the triangular patch model with body of revolution model results for problems involving scattering by spheres and cylinders having uniform or anisotropic impedance boundary conditions. [Vol. 10, No. 3 (1995), Special Issue on Advances in the Application of Method of Moments to Electromagnetic Radiation and Scattering Problems, pp 93-106]
Author(s): Allen W. Glisson, Mark Orman, Frank Falco, Donald Koppel
File Type: Journal Paper
Issue:Volume: 10      Number: 3      Year: 1995
Download Link:Click here to download PDF     File Size: 1128 KB

Title: PARAMETRIC MAPPING OF VECTOR BASIS FUNCTIONS FOR SURFACE INTEGRAL EQUATION FORMULATIONS
Abstract: A parametric mapping of vector basis functions is presented for curved-patch discretizations of surface integral equations. The mapping of the vector basis function maintains the normal continuity of the surface current density at cell boundaries, and is therefore suitable for use with the electric-field integral equation. Expressions for the matrix elements associated with the electric and magnetic field integral equations are developed. [Vol. 10, No. 3 (1995), Special Issue on Advances in the Application of Method of Moments to Electromagnetic Radiation and Scattering Problems, pp 107-115]
Author(s): Andrew F. Peterson, Keith R. Aberegg
File Type: Journal Paper
Issue:Volume: 10      Number: 3      Year: 1995
Download Link:Click here to download PDF     File Size: 632 KB

Title: A TECHNIQUE FOR AVOIDING THE EFIE "INTERIOR RESONANCE" PROBLEM APPLIED TO AN MM SOLUTION OF ELECTROMAGNETIC RADIATION FROM BODIES OF REVOLUTION
Abstract: Various surface integral equation formulations, including the electric (EFIE) and magnetic (MFIE) field integral equations, suffer from what is commonly known as the "interior resonance" problem. There are a number of remedies to this problem of which many involve modifying the integral equation formulation and result in increased computational effort and computer storage re- quirements. In an attempt to avoid this the application of a remedy, proposed in the literature, which requires no modification to the formulation has been investigated. This involves the detection of interior resonance frequencies and correction of the current by removing the mode responsible for the 'interior resonance". In the literature, the success of the remedy has been demonstrated for two-dimensional scattering problems involving PEC cylinders. In this work it is demonstrated that, while the correction of the MM (moment method) solution is successful when an "interior resonance" has been detected, the detection of the interior resonance frequencies can be extremely difficult in an MM solution of radiation from composite bodies of revolution. In fact, a foolproof computational algorithm for detecting interior resonance frequencies for this class of problems is yet to be developed. [Vol. 10, No. 3 (1995), Special Issue on Advances in the Application of Method of Moments to Electromagnetic Radiation and Scattering Problems, pp 116-128
Author(s): Pierre Steyn, David B. Davidson
File Type: Journal Paper
Issue:Volume: 10      Number: 3      Year: 1995
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Title: COMPUTATION OF MULTIPOLE MOMENTS FOR SHORT THIN WIRE CHIRAL STRUCTURES
Abstract: This paper considers the computation of the multipole moments of small chiral wire structures. The multipole moments are reviewed and it is shown that the charge induced on the wire must be accurately computed. A quasistatic thin-wire Galerkin Method of Moments formulation has been developed to numerically compute the charge distribution. The chiral structures under consideration are on the borderline of "thin" and a Body of Revolution Method of Moments formulation has also been developed for use as a check on the accuracy of the thin-wire approximations. It is shown that the "standard" thin-wire formulation is not sufficiently accurate, but the relatively simple addition of an end-cap greatly improves the convergence and accuracy of the formulation with acceptable computation cost. Finally, the formulation is extended to include bent wires, permitting the electric and magnetic dipole moments as well as the electric quadrupole moment to be calculated for a small chiral structure. [Vol. 10, No. 3 (1995), Special Issue on Advances in the Application of Method of Moments to Electromagnetic Radiation and Scattering Problems, pp 129-138]
Author(s): Isak Petrus Theron, David Bruce Davidson, Johannes Hendrik Cloete
File Type: Journal Paper
Issue:Volume: 10      Number: 3      Year: 1995
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Title: APPLICATION OF THE UMOM FOR THE COMPUTATION OF THE SCATTERING BY DIELECTRICS COATED WITH WEAKLY NONLINEAR LAYERS
Abstract: The paper describes an iterative approach to the computation of the electromagnetic scattering by isotropic, dielectric objects partially made of weakly nonlinear materials The approach is started by using a perturbative moment-method solution based on the Sherman-MorrisonWoodbury formula. The nonlinearity is assumed to be of the Kerr type, i e, the dielectric permittivity depends on the square amplitude of the electric field The bistatic scattering width and the field distribution are computed for some test cases, in particular, for infinite cylinders coated and filled with nonlinear materials The convergence of the medium is numerically evaluated and the results are compared with those obtained by the iterative distorted-wave Born approximation. [Vol. 10, No. 3 (1995), Special Issue on Advances in the Application of Method of Moments to Electromagnetic Radiation and Scattering Problems, pp 139-145]
Author(s): Salvatore Caorsi, Andrea Massa, Matteo Pastorino
File Type: Journal Paper
Issue:Volume: 10      Number: 3      Year: 1995
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Title: EM SIMULATION OF PACKAGED MMIC AND MICROSTRIP ANTENNAS USING "MICROWAVE EXPLORER"
Abstract: A moment method solution is presented for the full-wave electromagnetics analysis of multilayered planar structures of arbitrary shape. The mathematical formulation is based on the spectral domain integral equation and the Galerkin's testing procedure. The method is applied to shielded MMIC as well as radiating systems in the open environment. The inclusion of vertical current elements in the solution enables the method to analyze structures with vias and air bridges in both packaged and open environments Since a periodic structure approach is used in the formulation, extension to the analysis of infinite and finite antenna arrays becomes rather straightforward. Simulated results, obtained from our electromagnetic simulator "Microwave Explorer," are presented and compared with the available data to demonstrate the versatility and the accuracy of the method The numerical results presented include S-- parameters and farfield data. [Vol. 10, No. 3 (1995), Special Issue on Advances in the Application of Method of Moments to Electromagnetic Radiation and Scattering Problems, pp 146-152]
Author(s): Ali Sadigh, Krishnamoorthy Kottapalli, Peter Petre
File Type: Journal Paper
Issue:Volume: 10      Number: 3      Year: 1995
Download Link:Click here to download PDF     File Size: 479 KB