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Title: THE NEC2 RADIATION PATTERNS OF UNDER-SEGMENTED WIRE GRID MODELS OF A FIGHTER AIRCRAFT COMPARED TO MEASUREMENTS
Abstract: This paper presents results of a NEC2 method of moments evaluation of VHF/UHF antennas on a wire grid model of a fighter aircraft. The study shows that practically useful radiation patterns results can be obtained when the grid model is considerably under-segmented in aircraft regions which are electrically far removed from the antennas. Normal modelling guide-lines requires approximately 35000 segments for the fighter grid model at 400 MHz; judicious under-segmentation gave useful results using a model comprising 5000 segments. This reduction in segments reduced computer time by a factor of 343 and memory requirements is reduced by a factor of 18. NEC2 radiation patterns are compared to measurements on a l/lOth scale model which was performed in an anechoic chamber compact range. [Vol. 10, No. 1 (1995), pp 5-14]
Author(s): 0. Givati, A.P.C. Fourie
File Type: Journal Paper
Issue:Volume: 10      Number: 1      Year: 1995
Download Link:Click here to download PDF     File Size: 667 KB

Title: A SURFACE INTEGRAL EQUATION FORMULATION FOR LOW CONTRAST SCATTERERS BASED ON RADIATION CURRENTS
Abstract: A new surface integral equation formulation based on radiation currents is presented. Numerical problems have been observed when treating low contrast scatterers with surface integral equation formulations based on the total equivalent currents. These problems result because the total equivalent currents are large compared with the radiation currents for low contrast materials. The surface integral equation formulation presented here avoids this problem by solving directly for the radiation currents. [Vol. 10, No. 1 (1995), pp 15-18]
Author(s): Paul M. Goggans, Allen W. Glisson
File Type: Journal Paper
Issue:Volume: 10      Number: 1      Year: 1995
Download Link:Click here to download PDF     File Size: 423 KB

Title: THE MEASURED EQUATION OF INVARIANCE METHOD APPLIED TO RANDOMLY ROUGH SURFACES
Abstract: The Measured Equation of Invariance (MEI) method has received considerable attention recently. Unlike more traditional numerical techniques, MEI solutions are obtained by inversion of a relatively small and sparse matrix. Therefore, the MEI method can potentially provide a solution much more quickly than other techniques. To date, the MEI method has been applied primarily to discrete objects. In this paper, bistatic radar cross sections for one-dimensional, perfectly conducting, randomly rough surfaces are obtained using the MEI method. The implementation suitable for this problem requires some modification and enhancement of the original algorithm to achieve the desired accuracy. These algorithmic changes can be applied to the discrete scattering problem as well. Monte Carlo results for the bistatic scattering cross section for surfaces with Gaussian statistics and satisfying a Gaussian roughness spectrum are compared to those from another technique and excellent agreement is obtained. [Vol. 10, No. 1 (1995), pp 19-30]
Author(s): John B. Schneider, Shira Lynn Broschat
File Type: Journal Paper
Issue:Volume: 10      Number: 1      Year: 1995
Download Link:Click here to download PDF     File Size: 1519 KB

Title: WIREGRID: A NEC2 PRE-PROCESSOR
Abstract: WIREGRID is a pre-processor for the widely used public domain method of moments computer code NEC2. WIREGRID was developed for modelling metallic structures using a mesh of wires. In particular, it has powerful facilities for controlling the density of the mesh, permitting the same basic model to be used for different frequencies, with the code automatically generating a suitable mesh for a particular frequency. WIREGRID is not limited to generating wire meshes: it can also be usefully applied to true thin-wire modelling, for instance for Yagi-Uda and log-periodic antennas. In this paper, the basic philosophy of the code is described, and the code capabilities are detailed. Sufficient detail is presented so that the paper can serve as a reference for code users. The meshing algorithm is briefly described. An example is shown of the automatic mesh generation capabilities applied to an automobile. WIREGRID is available in the public domain via anonymous ftp; details of the ftp sites and hardware requirements are given in the appendices. [Vol. 10, No. 1 (1995), pp 31-39]
Author(s): C. F. du Toit, D.B. Davidson
File Type: Journal Paper
Issue:Volume: 10      Number: 1      Year: 1995
Download Link:Click here to download PDF     File Size: 844 KB

Title: A GUIDE TO IMPLEMENTATIONAL ASPECTS OF THE SPATIAL DOMAIN INTEGRAL EQUATION ANALYSIS OF MICROSTRIP ANTENNAS
Abstract: In the analysis of microstrip radiating structures integral equation methods rate among the more accurate approaches. By far the most demanding part in the use of these methods is the actual numerical implementation. This paper presents a detailed illustrated description of the numerical implementation of a spatial domain mixed-potential integral equation analysis of microstrip radiating structures. [Vol. 10, No. 1 (1995), pp 40-51]
Author(s): Louis T. Hildebrand, Derek A. McNamara
File Type: Journal Paper
Issue:Volume: 10      Number: 1      Year: 1995
Download Link:Click here to download PDF     File Size: 1533 KB

Title: PERFORMANCE OF A CHARACTERISTIC-BASED, 3-D, TIME-DOMAIN MAXWELL EQUATIONS SOLVER ON THE INTEL TOUCHSTONE DELTA
Abstract: A characteristic-based, windward numerical procedure for solving three-dimensional Maxwell equations in the time domain has been successfully ported to the Intel Touchstone Delta multicomputer. The numerical results by concurrent computation duplicated the earlier simulations of an oscillating electric dipole on a vector processor and compared well with the exact solutions. The parallelized code is scalable up to 512 nodes and incurs only up to 7.6% performance degradation. The sustained data processing rate is clocked at 6.551 Gigaops. However, the data I/O process is unscalable on the shared memory system. [Vol. 10, No. 1 (1995), pp 52-62]
Author(s): J. S. Shang, Kueichien C. Hill, Donald A. Calahan
File Type: Journal Paper
Issue:Volume: 10      Number: 1      Year: 1995
Download Link:Click here to download PDF     File Size: 1094 KB

Title: ON THE APPLICABILITY OF THE BICONJUGATE GRADIENT FFT METHOD FOR THE THIN CONDUCTING PLATE PROBLEM
Abstract: The application of the Biconjugate Gradient FFT method to the thin conducting plate problem is investigated. Upon comparing with a Conjugate Gradient FFT method, it is found that the Biconjugate Gradient solution requires a relatively larger error tolerance to achieve a comparatively well-behaved current distribution. Coupled with the requirement of only one matrix-vector product per iteration, the computational cost of the Biconjugate Gradient method is, thus, much smaller than those previously reported in the literature. Of particular importance is the use of the incident electric field as a starting estimate to alleviate the non-convergence behaviour which is usually associated with the application of a Biconjugate Gradient approach to conducting plates at grazing angle. For other angles of incidence, it is shown that this procedure also accelerates the resulting convergence rates as compared to those obtained by simply using zero as an initial estimate. [Vol. 10, No. 1 (1995), pp 63-68]
Author(s): T. V. TRAN, A. McCOWEN
File Type: Journal Paper
Issue:Volume: 10      Number: 1      Year: 1995
Download Link:Click here to download PDF     File Size: 702 KB