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Title: ON THE USE OF BIVARIATE SPLINE INTERPOLATION OF SLOT DATA IN THE DESIGN OF SLOTTED WAVEGUIDE ARRAYS
Abstract: Essential to the design process of slotted waveguide arrays is an accurate knowledge of the self-properties of the individual slots. These properties can be computed with sufficient accuracy using moment method codes, which are too computationally intensive to be incorporated into design codes for large arrays. This paper describes an interpolation scheme which provides both sufficiently accurate, and rapid, computation of slot data from a pre-determined database to be viable for use in a slotted waveguide array design code. [Vol. 9, No. 1 (1994), pp 6-9]
Author(s): Derek A. McNamara, Johan Joubert
File Type: Journal Paper
Issue:Volume: 9      Number: 1      Year: 1994
Download Link:Click here to download PDF     File Size: 335 KB

Title: A TECHNIQUE FOR DETERMINING NON-INTEGER EIGENVALUES FOR SOLUTIONS OF ORDINARY DIFFERENTIAL EQUATIONS
Abstract: A study of the determination of non-integer eigenvalues for ordinary differential equations with transcendental solutions is presented. An algorithm based on expansion in terms of Chebyshev polynomials and collocation is presented. The method is applied to the problem of computing the electric field external to a biconical radiating structure. Eigenfunction solutions for Legendre's differential equation satisfying the boundary conditions of the problem considered are presented. [Vol. 9, No. 1 (1994), pp 10-17]
Author(s): D. Reuster, M. Kaye
File Type: Journal Paper
Issue:Volume: 9      Number: 1      Year: 1994
Download Link:Click here to download PDF     File Size: 351 KB

Title: ANTENNA MODELING AND CHARACTERIZATION OF A VLF AIRBORNE DUAL TRAILING WIRE ANTENNA SYSTEM
Abstract: This paper describes the electrical characterization of the Very Low Frequency (VLF) dual trailing wire antenna systems associated with Navy aircraft used for communications to underwater Navy assets. The static wire geometry with the aircraft in orbit was obtained using a modified version of the program WIRE3, which models the mechanical parameters of the dual trailing wire antenna. The Numerical Electromagnetics Code (NEC) was used to model all electrical characteristics of the VLF dual trailing wire systems associated with the typical TACAMO aircraft. Antenna parameters such as current distribution, input impedance versus frequency, effective radiated power, and the effect of antenna wire conductivity were evaluated. It is demonstrated that the computer codes provide results which are consistent with measured values of static antenna electrical parameters. [Vol. 9, No. 1 (1994), pp 18-31]
Author(s): J.K. Breakall, D.H. Werner, R.J. Lunnen
File Type: Journal Paper
Issue:Volume: 9      Number: 1      Year: 1994
Download Link:Click here to download PDF     File Size: 675 KB

Title: ELECTROMAGNETIC SCATTERING FROM TWO-DIMENSIONAL COMPOSITE OBJECTS
Abstract: Different surface integral equations are presented for two- dimensional composite objects. The objects consist of impedance bodies partially coated with dielectric materials. In all of the formulations, the impedance boundary condition is applied on the impedance surface to reduce the matrix size in the numerical solution. The integral equations are reduced to a system of linear equations via the point matching technique. Application of the point matching technique is straight forward for two dimensional objects. Because of this surface discontinuities can be treated easily without the problems encountered when using triangle basis functions as a result, consideration of two-dimensional objects gives a clear picture of the accuracy that can be obtained using these formulations. Two of the formulations discussed herein overcome the problem of internal resonance. The numerical solutions are verified either by comparison with the analytical solutions for cylindrical objects or by applying self consistency tests for targets without analytical solutions. [Vol. 9, No. 1 (1994), pp 32- 39]
Author(s): Ahmed A. Kishk, Paul M. Goggans
File Type: Journal Paper
Issue:Volume: 9      Number: 1      Year: 1994
Download Link:Click here to download PDF     File Size: 583 KB

Title: EFFICIENT MATRIX ELEMENT CALCULATIONS FOR THE SPECTRAL DOMAIN METHOD APPLIED TO SYMMETRICAL MULTICONDUCTOR TRANSMISSION LINES
Abstract: The spectral domain method has proved to be a suitable analytical tool for the characterization of open, symmetrical planar structures. The method requires the repeated calculation of matrix elements, which each involves the time-consuming process of numerical integration over an infinite range. In this paper, suitable basis functions for the expansion of electric surface currents on strips or electric fields in slots, are provided. It is also shown how the use of these basis functions makes possible the efficient and rapid calculation of the matrix elements. [Vol. 9, No. 1 (1994), pp 40-50]
Author(s): J.C. Coetzee, J.A.G. Malherbe
File Type: Journal Paper
Issue:Volume: 9      Number: 1      Year: 1994
Download Link:Click here to download PDF     File Size: 583 KB

Title: PARALLEL IMPLEMENTATION OF THE NUMERICAL ELECTROMAGNETICS CODE
Abstract: NEC2 is a 10 000 line, public domain, FORTRAN IV program for electromagnetic analysis. This program has been adapted for use on transputer networks of various dimension. The FORTRAN code has been modified and translated into OCCAM where necessary. Parallel algorithms were developed and implemented for each NEC2 function in order to optimise efficiency. Execution efficiencies in excess of 80% were attained. [Vol. 9, No. 1 (1994), pp 51-57]
Author(s): D.C. Nitch, A.P.C. Fourie
File Type: Journal Paper
Issue:Volume: 9      Number: 1      Year: 1994
Download Link:Click here to download PDF     File Size: 544 KB

Title: VALIDATION OF THE MININEC3 CODE FOR COMPLEX RADIATING STRUCTURES
Abstract: The ability of the MININEC3 code to accurately model complex radiating structures was previously unknown because computer compiler constraints limited the size of analyzable configuration. With the conversion of the code from BASIC to FORTRAN however it is now feasible to use it to simulate such structures. This paper presents the results of a validation exercise aimed at assessing the code's suitability for modelling configurations which involve hundreds of segments. [Vol. 9, No. 1 (1994), pp 58-66]
Author(s): K.P. Murray, B.A. Austin
File Type: Journal Paper
Issue:Volume: 9      Number: 1      Year: 1994
Download Link:Click here to download PDF     File Size: 771 KB

Title: SOME EXAMPLES OF THE PREDICTION AND VALIDATION OF NEAR-FIELD DEPENDENT AIRCRAFT HF ANTENNA PARAMETERS USING NEC
Abstract: Examples are presented of the application of a moment- method modelling procedure (using NEC) to calculate the near-field dependent parameters of aircraft HF antennas. The overall aim of the work from which the examples are drawn is to provide a 'recipe'; the application of which will generate predictions of parameters of interest which are both credible and sufficiently accurate for engineering purposes. A feature of the procedure is that no empirically derived information is incorporated. The examples encompass a range of generic aircraft and antenna types: both fixed and rotary wing airframes, and electric (wire) and magnetic (loop and notch) primary radiators. Particular emphasis is placed upon validation of the predictions. This is performed by direct measurement where possible, but where this is not practicable simple, but independent, calculations are performed based upon equivalent circuits. As for the moment-method procedure, these corroborative calculations do not depend upon empirical information. [Vol. 9, No. 1 (1994), pp 67-77]
Author(s): J.W.R. Cox
File Type: Journal Paper
Issue:Volume: 9      Number: 1      Year: 1994
Download Link:Click here to download PDF     File Size: 970 KB

Title: USE OF A STEALTH BOUNDARY WITH FINITE DIFFERENCE FREQUENCY DOMAIN SIMULATIONS OF SIMPLE ANTENNA PROBLEMS
Abstract: A direct method for the numerical solution of Maxwell's equations in the frequency domain (sinusoidal steady state), for radiation problems of cylindrical symmetry, is incorporated into a finite difference program called HERZ, coded in FORTRAN. The termination of the fields on the outer boundary of the problem domain is accomplished via an absorptive layer, labelled a stealth layer, which attenuates the incident fields to insignificant amounts in a small computing space, without causing significant reflections that would disturb the near field solutions. No radiation boundary condition is specified on the problem domain, rather, the transmission of the fields to the stealth layer is optimized by specifying its electrical properties. To validate HERZ as a useful electromagnetic modeller for thin wire antennas, driving point admittances and surface current distributions for several configurations were compared to both theoretical and measured values, with good agreement. [Vol. 9, No. 1 (1994), pp 78-87]
Author(s): R.B. Thompson, F.S. Chute, F.E. Vermeulen
File Type: Journal Paper
Issue:Volume: 9      Number: 1      Year: 1994
Download Link:Click here to download PDF     File Size: 794 KB

Title: TWO WIRE RHOMBIC ILLUMINATOR PERFORMANCE AS PREDICTED BY THEORETICAL AND NUMERICAL MODELS
Abstract: The two wire rhombic illuminator (RI) is a rhombic wire antenna located over a ground plane which is used to generate near uniform electromagnetic fields over a specified working volume located below the antenna. The RI can be modeled as a simple two-wire transmission line at low frequencies but the transmission line model becomes inadequate at higher frequencies due to the enhanced radiation properties of the antenna. The performance of the RI including radiation effects is evaluated numerically using the Numerical Electromagnetics Code (NEC-2) and compared to that of the transmission line model. The antenna in the presence of a perfectly conducting ground plane is analyzed at frequencies ranging from 1 MHz to 500 MHz. Various segmentation schemes are utilized in order to accurately predict the performance of the RI at frequencies where the dimensions of the structure are very large in terms of wavelength. [Vol. 9, No. 1 (1994), pp 88- 101]
Author(s): J. Patrick Donohoe, Saad N. Tabet, C.D. Taylor
File Type: Journal Paper
Issue:Volume: 9      Number: 1      Year: 1994
Download Link:Click here to download PDF     File Size: 782 KB