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Title: ABOUT THE STUDY IN THE TIME DOMAIN OF JUNCTIONS BETWEEN THIN WIRES
Abstract: DOTIGl is a computer code developed for the study of the interaction of arbitrary electromagnetic signals with thin-wire structures, in the time domain. It calculates the current distribution induced on the structure by solving the electric field integral equation using the moment method. The numerical procedure used to develop the program and different possibilities for treating junctions are briefly described. To obtain an accurate solution for the current induced on the thin-wire structures it is very important to pay attention to the zones at which the wires intersect. Thus, different junction treatments were tested for several simple structures. Following some convergence criteria the current distributions were compared to a reference solution and also, by way of Fourier transform, with results obtained using some well known frequency-domain codes. [Vol. 6, No. 2, pp. 2-20 (199l)]
Author(s): Amelia Rubio Bretones, Alfonso Salinas Extremera
File Type: Journal Paper
Issue:Volume: 6      Number: 2      Year: 1991
Download Link:Click here to download PDF     File Size: 567 KB

Title: OPTIMAL LOCATION FOR MATCHING POINTS FOR WIRE MODELLING WITH MMP
Abstract: It is a basic premise in electromagnetic field modelling that the tangential electromagnetic field on the surface of ideal conductors must vanish. When point matching is used to impose this condition, the location of the matching points must be chosen. This paper treats the special case of thin wires. It is shown that for common approximations of the wire currents, the optimum locations of the matching points are well defined and that forcing the boundary condition beside these well defined matching points would increase the errors. For both piecewise-linear and staircase approximation of the current, explicit formulae for the optimum location of the matching points are given. [Vol. 6, No. 2, pp. 21-37 (1991)]
Author(s): P. Leuchtmann
File Type: Journal Paper
Issue:Volume: 6      Number: 2      Year: 1991
Download Link:Click here to download PDF     File Size: 707 KB

Title: SURFACE MODELLING FOR EM INTERACTION ANALYSIS
Abstract: This paper deals with the numerical modelling of the surface of a structure with a wire grid or a surface patch for Electromagnetic (EM) interaction analysis. Surface currents and fields on a wire grid model are computed using the Numerical Electromagnetics Code (NEC). The results are compared with those obtained on a triangular surface patch model using an Electric Field Integral Equation (EFIE) formulation. Simple structures such as a square plate as well as complicated structures such as an aircraft are considered. Good agreement is obtained in most cases. [Vol. 6, No. 2, pp. 38-52 (l99l)]
Author(s): S. Kashyap, A. Loule
File Type: Journal Paper
Issue:Volume: 6      Number: 2      Year: 1991
Download Link:Click here to download PDF     File Size: 587 KB

Title: ON THE FUNCTIONING OF A HELICOPTER-BORNE HF LOOP ANTENNA
Abstract: Numerical techniques allow engineers to evaluate the performance of antennas on complex structures. These techniques can provide valuable physical insights into the overall functional performance of such antennas. This short paper reports on the use of NEC2 to investigate the radiation characteristics of a loop antenna mounted below the tailboom of a helicopter in the frequency band 2AE15 MHz. It was concluded that such a loop antenna serves mainly to excite a dominant electrical dipole mode of operation for frequencies less than the lowest natural electrical resonance frequency of the helicopter itself, but greater than some frequency near the low end of the HF band. A limited set of measurements performed on a scale model of a helicopter generally supports the conclusions drawn from the numerical results predicted using NEC2. The reported result is of importance in so-called 'nap-of- the-earth' HF communications from helicopters. [Vol. 6, No. 2, pp. 53-73 (l99l)]
Author(s): Duncan C. Baker
File Type: Journal Paper
Issue:Volume: 6      Number: 2      Year: 1991
Download Link:Click here to download PDF     File Size: 1130 KB

Title: THE LINEAR-PHASE TRIANGULAR FACET APPROXIMATION IN PHYSICAL OPTICS ANALYSIS OF REFLECTOR ANTENNAS
Abstract: Numerical analysis of reflector antennas uses a discrete approximation of the radiation integral. The calculation replaces the actual reflector surface with a triangular facet representation. The physical optics current is then approximated within each facet. This paper provides analytical details of the method based on the assumption of a constant magnitude and linear-phase approximation of the physical optics current. Example calculations are provided for parabolic, elliptical, and shaped subreflectors. The computed results are compared with calculations made using a constant-phase approximation. These results show that the linear-phase approximation is a significant improvement over the constant-phase approximation in that the solution converges over a larger angular region of space. This improvement can significantly reduce storage requirements and possibly execution speed. [Vol. 6, No. 2, pp. 74-85 (1991)]
Author(s): W. A. Imbriale, R. E. Hodges
File Type: Journal Paper
Issue:Volume: 6      Number: 2      Year: 1991
Download Link:Click here to download PDF     File Size: 409 KB

Title: SIMPLIFIED 3-D MESH GENERATOR
Abstract: Wire-grid modelling of continuous surfaces for structures in three dimensions is a tedious and time consuming process. This paper describes a simplified automatic mesh generator that converts a large class of three-dimensional structures into appropriate wire-grid models. The output of the generator can readily be used as the input to wire antenna Moment Method codes. It is however designed specifically for use with the Numerical Electromagnetics Code (NEC). [Vol. 6, No. 2, pp. 86-98 (l991)]
Author(s): Riyadh K. Najm
File Type: Journal Paper
Issue:Volume: 6      Number: 2      Year: 1991
Download Link:Click here to download PDF     File Size: 562 KB

Title: THE SHORT FAT DIPOLE DEVELOPMENT IN APL OF A MOM SOLUTION
Abstract: This paper describes an effort to find the best profile for a figure-of- revolution, center-fed, electrically small dipole. It includes presentations on equation development, singularity treatment, code development, verification, and performance. [Vol. 6, No. 2, pp. 99-132 (1991)]
Author(s): Douglas B. Miron
File Type: Journal Paper
Issue:Volume: 6      Number: 2      Year: 1991
Download Link:Click here to download PDF     File Size: 1697 KB

Title: ANALYSIS OF THREE DIMENSIONAL DIELECTRIC LOADED CAVITIES WITH EDGE ELEMENTS
Abstract: In this paper we show that edge elements (a class of mixed finite elements) provide an efficient numerical approach in the determination of resonant modes in three dimensional high frequency cavities. These finite elements avoid "spurious modes", the non-physical numerical fields obtained from the solution of eigenvalue problems. Here, empty cavities as well as dielectric loaded cavities are analyzed: no "spurious mode" was observed. Moreover, comparisons with analytical results and previously published ones show the great accuracy of the numerical technique. [Vol. 6, No. 2, pp. 133-142 (1991)]
Author(s): L. Pichon, A. Razek
File Type: Journal Paper
Issue:Volume: 6      Number: 2      Year: 1991
Download Link:Click here to download PDF     File Size: 1475 KB

Title: ANTENNA ARRAY MODELLING BY PARALLEL PROCESSOR FARMS
Abstract: The fast concurrent implementation of a FORTRAN method of moments analysis of the electromagnetic properties of an array of tapered slot antennae is discussed. Decomposition of an existing FORTRAN algorithm for calculation of the currents induced by an incident radiation field in an infinite array of tapered slot antennae is described. The problem was distributed across an array of INMOS transputers, yielding significant speed-up over a single CPU. This decomposition was relatively simple to implement, can readily be scaled to larger processor arrays virtually indefinitely, and promises linear speed-up with the number of processors in the array. [Vol. 6, No. 2, pp. 143-151 (l991)]
Author(s): Iain Cramb, Daniel H. Schaubert, Richard Beton, James Kingdon, Colin Upstill
File Type: Journal Paper
Issue:Volume: 6      Number: 2      Year: 1991
Download Link:Click here to download PDF     File Size: 1473 KB