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Title: REVISED INTEGRATION METHODS IN A GALERKIN BOR PROCEDURE
Abstract: Several relatively simple numerical changes improve the speed and accuracy of the early Mautz and Harrington discretization procedure for boundary element method calculations of scattering from axially symmetric bodies. This method is still in common use in programs such as CICERO and GRMBOR. For a fixed set of geometry points, changes in the azimuthal (o) integration reduce computer time, especially when lossy materials are involved. Changes in the integration along the generating curve (t) improve accuracy. The most interesting of these is the use of the equal area rule from parallel wire modeling of solid surfaces to answer the old question of the optimal constant for dealing with an integrable singularity in some of the t integrals. Some of these changes are applicable to a variety of integral equations and boundary conditions. Most of them can be implemented with little programming effort. Tests are shown for difficult cases involving spheres, and Mie series calculations are used for comparison. [Vol. 10, No. 2 (1995), pp 5-16]
Author(s): David R. Ingham
File Type: Journal Paper
Issue:Volume: 10      Number: 2      Year: 1995
Download Link:Click here to download PDF     File Size: 886 KB

Title: HIGHER-ORDER FDTD METHODS FOR LARGE PROBLEMS
Abstract: The Finite-Difference Time-Domain (FDTD) algorithm provides a simple and efficient means of solving Maxwell's equations for a wide variety of problems. In Yee's uniform grid FDTD algorithm the derivatives in Maxwell's curl equations are replaced by central difference approximations. Unfortunately, numerical dispersion and grid anisotropy are inherent to FDTD methods. For large computational domains, e.g., ones that have at least one dimension forty wavelengths or larger, phase errors from dispersion and grid anisotropy in the Yee algorithm (YA) can be significant unless a small spatial discretization is used. For such problems, the amount of data that must be stored and calculated at each iteration can lead to prohibitive memory requirements and high computational cost. To decrease the expense of FDTD simulations for large scattering problems two higher-order methods have been derived and are reported here. One method is second-order in time and fourth-order in space (2-4); the other is second-order in time and sixth-order in space (2-6). Both methods decrease grid anisotropy and have less dispersion than the YA at a set discretization. Also, both permit a coarser discretization than the YA for a given error bound. To compare the accuracy of the YA and higher-order methods both transient and CW simulations have been performed at a set discretization. In general, it has been found that the higher-order methods are more accurate than the YA due to the reduced grid anisotropy and dispersion. However, the higher-order methods are not as accurate as the YA for the simulation of surface waves. This is attributed to the larger spatial stencil used in calculating the fields for the higher-order methods. More research is needed to examine the accuracy of higher-order methods at material boundaries. [Vol. 10, No. 2 (1995), pp 17-29]
Author(s): Charles W. Manry Jr, Shira L. Broschat, John B. Schneider
File Type: Journal Paper
Issue:Volume: 10      Number: 2      Year: 1995
Download Link:Click here to download PDF     File Size: 1102 KB

Title: RADAR CROSS SECTION OF A RECTANGULAR CAVITY- A MASSIVELY PARALLEL CALCULATION
Abstract: A sequential code that calculates the radar cross section of a rectangular waveguide cavity was modified to execute on a MasPar MP-l massively parallel computer with a SIMD architecture. The code uses the mode matching method of analysis to produce a set of matrix equations. Steps taken to accomplish the parallelization are discussed and some specific examples of program modification are presented. Timing results for wideband data are given that demonstrate the power of parallel computers for this type of application. Suggestions are made for further improvements as increased memory space becomes available. [Vol. 10, No. 2 (1995), pp 30-45]
Author(s): L. D. Vann, L.T. Willet, J.S. Bagby, H.F. Helmken
File Type: Journal Paper
Issue:Volume: 10      Number: 2      Year: 1995
Download Link:Click here to download PDF     File Size: 835 KB

Title: A NUMERICAL TECHNIQUE TO DETERMINE ANTENNA PHASE CENTER LOCATION FROM COMPUTED OR MEASURED PHASE DATA
Abstract: In many antenna applications, it is a requirement to have knowledge of the antenna phase center properties. Many interpretations of antenna phase center and its apparent location exist. This paper will present a formulation for determination of antenna phase center location derived using the antenna phase response. A fortran program, developed from the formulations, is used to calculate phase center location for several examples which include both computed and simulated measured phase data. A simple numerical technique is presented that processes measured phase data allowing accurate phase center determination. [Vol. 10, No. 2 (1995), pp 46-62]
Author(s): Steven R. Best, James M. Tranquilla
File Type: Journal Paper
Issue:Volume: 10      Number: 2      Year: 1995
Download Link:Click here to download PDF     File Size: 1044 KB

Title: CONFORMAL ARRAY DESIGN SOFTWARE
Abstract: A powerful conformal array design computer program can be developed by modification of a physical optics based array fed reflector analysis computer program. [Vol. 10, No. 2 (1995), pp 63-74]
Author(s): H.K. Schuman
File Type: Journal Paper
Issue:Volume: 10      Number: 2      Year: 1995
Download Link:Click here to download PDF     File Size: 556 KB

Title: COMPARISON OF THE INPUT IMPEDANCE OF MONOPOLE ANTENNAS OBTAINED BY NEC, MINlNEC, AND MEASUREMENTS
Abstract: This paper compares the input impedance of monopole antennas numerically calculated by NEC and MININEC with experimental results. This comparison determines the limitation of these two computer codes used for modeling more complicated structures. Two groups of monopoles are considered. The first group consists of eight electrically thin monopoles of length .28 meters (.235 wavelengths at 252 MHz) and radii of .4064, . 7874, 1.168, 1.562, 2.390, 3.162, 6.350, and 7.920 millimeters (.341E-3, .661E-3, .981E-3, 1.31E-3, 2.01E-3, 2.66E-3, 5.33E-3, and 6.65E-3 wavelengths at 252 MHz). For this group, impedance calculations were compared to measurements over the band of 237-267 MHz. The second group consists of five electrically thick monopoles of length .2 wavelengths and radii of .0509, .0635, .0847, .1129, and .1270 wavelengths. For the second group impedance calculations were compared with measurements of tubular monopoles with flat ends. The results of this paper show that the extended kernel option of NEC predicted measured monopole impedance measurements more accurately than MININEC. [Vol. 10, No. 2 (1995), pp 75-85]
Author(s): R. J. Bauerle, J. K. Breakall
File Type: Journal Paper
Issue:Volume: 10      Number: 2      Year: 1995
Download Link:Click here to download PDF     File Size: 745 KB

Title: ACCURATE MODELING OF STEPPED-RADII ANTENNAS
Abstract: The LP8, eight element, log periodic antenna made by M2 Enterprises has recently been modeled at Penn State University using both Version 2 and 4 of the Numerical Electromagnetics Code (NEC). The antenna has a steppedradii element construction and operates from 10 to 30 MHz. The stepped-radii element construction is difficult to model using NEC Version 2. To model a stepped-radii antenna with this version, equivalent lengths of constant radii are calculated using another method of moments program called ELNEC. These equivalent lengths replaced the original stepped radii elements of the log periodic antenna during the modeling. Fortunately, NEC Version 4 can simulate the stepped-radii elements directly, which makes the modeling procedure much easier and accurate. Both NEC models show good agreement with the measurements when compared to VSWR measurements. The authors hope that this paper will help others with similar modeling problems who cannot yet obtain NEC Version 4. [Vol. 10, No. 2 (1995), pp 86-95]
Author(s): A. I. Bauerle, J. K. Breakall
File Type: Journal Paper
Issue:Volume: 10      Number: 2      Year: 1995
Download Link:Click here to download PDF     File Size: 726 KB

Title: MUTUAL VALIDATION OF THREE PROGRAMS FOR NUMERIC ANTENNA COMPUTATIONS
Abstract: The numerical results obtained by three different codes, GALNEC, WARAN and NEC-2 are compared for thin dipoles and thick ones with hemispherical end caps and for arrays of such collinear dipoles. The electric field integral equation and Galerkin's method are used in the code GALNEC where solid thick dipole bodies are implemented. Mei's (1965) integral equation and collocation technique are wed in the code WARAN, where thick dipoles are simulated as arrays of thin wires. Good agreement has been obtained for current distri- butions and input and mutual impedances. [Vol. 10, No. 2 (1995), pp 96-101]
Author(s): Andrew A. Efanov, Harald Schopf, Bernhard Schnizer
File Type: Journal Paper
Issue:Volume: 10      Number: 2      Year: 1995
Download Link:Click here to download PDF     File Size: 421 KB

Title: SIMPLE FINITE ELEMENT SOLUTIONS FOR EDDY CURRENT LOSSES IN PIPE-TYPE CABLES
Abstract: This paper outlines a simple finite element approach for computing eddy current losses in pipe-type cables Essentially, what is solved for is the eddy current loss in a metallic shell that encompasses one or more power frequency currents, flowing parallel to the longitudinal axis of the shell. The traditional cross sectional model for this type of problem involves an open boundary, which can present difficulties for conventional finite element methods, although some success has recently been reported with asymptotic boundary conditions [1]. For many practical cases, the simplest way to bypass this obstacle is to impose an approximate boundary condition, H= 0, at the outer surface of the metal shell It is demonstrated in this paper that this approximate boundary condition is quite accurate if the shell is, as a rule of thumb, at least three skin depths thick. [Vol. 10, No. 2 (1995), pp 102- 109]
Author(s): T. Loga, F.S. Chute, F.E. Vermeulen
File Type: Journal Paper
Issue:Volume: 10      Number: 2      Year: 1995
Download Link:Click here to download PDF     File Size: 805 KB