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Title: BACKSCATTERING FROM A CUBE
Abstract: Three analytical techniques -- the method of moments, geometrical theory of diffraction, and physical optics (without fringe current correction) -- are applied to the case of backscattering from a cube. Results are compared to experimental data. It is relatively easy to compute specular scattering with good accuracy; it is much more difficult to obtain good accuracy for corner incidence, which is emphasized here precisely because it provides a more rigorous test of an analytical technique. As expected, the method of moments provides good results when the segmentation is on the order of 0.1 wavelengths, and in some cases up to 0.26 wavelengths. Single-diffraction geometrical theory of diffraction predicts peak scattering within a few dB for a cube dimension of 0.1-3 wavelengths, which is the full range of experimental data, but is not accurate between peaks. Physical optics predictspeak scattering within a few dB for a cube dimension of 1-3 wavelengths, and is also not accurate between peaks. [Vol. 2, No. 2 pp. 55-74 (1987)]
Author(s): A. C. Ludwig
File Type: Journal Paper
Issue:Volume: 2      Number: 2      Year: 1987
Download Link:Click here to download PDF     File Size: 979 KB

Title: A NUMERICAL EXAMPLE OF A 2-D SCATTERING PROBLEM USING A SUBGRID
Abstract: In this paper we present a detailed application of a subgridding scheme for the finite difference time domain (FDTD) numerical solution to Maxwell's equations. The subgridding scheme will be necessary for greater detail and for localized calculations when other methods for the subcell modifications of the regular FDTD are not applicable. We have made comparative calculations, as a function of mesh size, of the reflection coefficient and shunt capacitance associated with two invite parallel plates with a finite discontinuity in plate separation. [Vol. 2, No. 2, pp. 75-102 (1987)]
Author(s): John C. Kasher, Kane S. Yee, Lawrence Livermore
File Type: Journal Paper
Issue:Volume: 2      Number: 2      Year: 1987
Download Link:Click here to download PDF     File Size: 1283 KB

Title: MODELLING BY NEC OF AN HF LOG-PERIODIC ANTENNA
Abstract: The Numerical Electromagnetics Code (NEC) is a computer code for analysing the electromagnetic response of an arbitrary structure consisting of wires and surfaces in free space or over a ground plane. It is based on the application of the Method of Moments to solve the electric field integral equation. A practical application of NEC which involved calculation of the impedance of a vertically polarised HF log- periodic antenna and comparison with measurements is described. A technique for improving the accuracy of the numerical calculations is discussed in addition to methods for accurately measuringmpedances of antennas employing balanced two-wire transmission line feeders. [Vol. 2, No. 2, pp. 103-111 (1987)]
Author(s): G. R. Haack
File Type: Journal Paper
Issue:Volume: 2      Number: 2      Year: 1987
Download Link:Click here to download PDF     File Size: 1080 KB

Title: THE COMPUTATION EXPRESSIONS OF SPHEROIDAL EIGENVALUES
Abstract: The higher order terms of eigenvalues in spheroidal differential equations are developed by using power-series expansion and asymptotic ones for both prolate and oblate wave functions. These important multipole expansions greatly facilitate and improve the computations of the electromagnetic scattering by different kinds of spheroids with various size parameters, refractive indices, and aspect ratios. [Vol. 2, No. 2, pp. 112-121 (1987)]
Author(s): Wan-xian Wang
File Type: Journal Paper
Issue:Volume: 2      Number: 2      Year: 1987
Download Link:Click here to download PDF     File Size: 601 KB

Title: NEAR FIELDS OF A LOGAEPERIODIC DIPOLE ANTENNA: NEC MODELLING AND COMPARISON WITH MEASUREMENTS
Abstract: Experiences of modelling a log-periodic antenna (tapered transmission line type) using NEC are reported. The antenna is required as a component of a near-field EMC test range, and hence computation of the near fields was the primary objective although some discussion of impedance is presented. Measurements of the near field of the real antenna were undertaken on a planar measurement range having the ability to scan planes at varying distances from the antenna. The measurements show good agreement with the predictions of NEC. [Vol. 2, No. 2, pp. 122-130 (1987)]
Author(s): K. T. Wong, P. S. Excell
File Type: Journal Paper
Issue:Volume: 2      Number: 2      Year: 1987
Download Link:Click here to download PDF     File Size: 773 KB

Title: THE APPLICATION OF THE CONJUGATE GRADIENT METHOD TO THE SOLUTION OF OPERATOR EQUATIONS -- AN UNCONVENTIONAL PERSPECTIVE
Abstract: This narrative presents an alternate philosophy for the accurate solution of operator equations, you might say "both singular and nonsingular" in general. In this approach, we try to solve the exact operator equation in an approximate way, quite differently from the matrix methods which try to solve the approximate operator equation in an exact fashion. The advantage of this new philosophy is that convergence is assured and a priori error estimates are available. The conjugate gradient methods are numerical methods which provide a means to reach this new goal, as opposed to an efficient means of just solving matrix equations, which some researchers have assumed them to be. We thereby take the position that there is a heaven-and-hell difference between the application of the conjugate gradient method to solve an operator equation and its application to the solution of matrix equations. [Vol. 2, No. 2, pp. 131-135 (1987)]
Author(s): Tapan K. Sarkar, Ercument Arvas
File Type: Journal Paper
Issue:Volume: 2      Number: 2      Year: 1987
Download Link:Click here to download PDF     File Size: 714 KB