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Title: A STABILIZING SCHEME FOR THE EXPLICIT TIME-DOMAIN INTEGRAL-EQUATION ALGORITHM
Abstract: The stability of the explicit version of the solution of the time-marching electric-field integral-equation continues to depend on the specifics of the application. The design of stability-enhancing schemes seems to be more of an art than a science. A contribution to this art is made with a design that is stable where others are not, and the practical issues of implementation, accuracy, and efficiency in both time and memory are addressed.
Author(s): S. Kashyap, M. Burton, A. Louie
File Type: Journal Paper
Issue:Volume: 13      Number: 3      Year: 1998
Download Link:Click here to download PDF     File Size: 757 KB

Title: BROAD BAND MODELLING OF ELECTROMAGNETIC WAVE COUPLING TO SCATTERERS INSIDE A METALLIC CAVITY
Abstract: In this paper we present an approach based on the method of moments for the solution of an electromagnetic compatibility problem. We determine the results of the impact of an electromagnetic wave on metallic housings with small holes. By separating the interior and the exterior of the housing we are able to use the Green’s functions of the cavity. The number of unknowns is therefore reduced compared to solutions using the free space Green’s functions. Different sets of functions (either local or global) are used for the method of moments (MoM). Furthermore, we present a method to generate broad band data from only a few computations by using an “intelligent” interpolation procedure. Finally, we present an experimental setup and compare our computations with measurements.
Author(s): J. v. Hagen, W. Tabbara, D. Lecointe
File Type: Journal Paper
Issue:Volume: 13      Number: 3      Year: 1998
Download Link:Click here to download PDF     File Size: 621 KB

Title: AN ALGORITHM FOR CALCULATING GREEN’S FUNCTIONS OF PLANAR, CIRCULAR CYLINDRICAL, AND SPHERICAL MULTILAYER SUBSTRATES
Abstract: We introduce an algorithm for calculating spectral domain Green’s functions of planar, circular, cylindrical, and spherical multilayer structures. The three spectral domain problems are interpreted as multilayer spatial domain problems with electromagnetic sources in the forms of current sheets, tubes, and shells, respectively, and with harmonic spatial variation. The algorithm, which is the same for all three geometries, is based on dividing these three field problems into appropriate subproblems by using equivalence, and on determining the tangential field components at the interfaces between the layers of the structure. The algorithm is implemented into three versions of a Fortran routine called G1DMULT, one version for each geometry. The only difference between the three versions is in two subroutines which calculate the fields due to harmonic current sheets, tubes, and shells, respectively, located in an infinite homogeneous material. We have tested the routine by calculating the properties of microstrip patch antennas and periodic structures.
Author(s): Zvonimir Šipuš, Per-Simon Kildal, Robert Leijon, Martin Johansson
File Type: Journal Paper
Issue:Volume: 13      Number: 3      Year: 1998
Download Link:Click here to download PDF     File Size: 955 KB

Title: DISCRETIZATION ERRORS IN THE GRAPHICAL COMPUTATION OF THE PHYSICAL OPTICS SURFACE INTEGRAL
Abstract: This paper studies the sources of discretization errors in the graphical computation of PO surface integrals. Three different PO models that as-sociate to screen pixels patches of different shape and orientation are presented. The RCS versus frequency results obtained for a sphere show that when the reso-lution in the surface discretization is high enough for the working frequency, the best results are obtained with the triangle mesh PO model (Gordon formula) [2], but the tangent plane approximation of J.S. Asvestas [13] achieves the best trade-off between CPU time and accu-racy. When the resolution in the surface discretization is not high enough for the working frequency, the best results are obtained in most cases with the heuristic ap-proximation of J.M. Rius [11] [12], due to the use of interpolated unit normals in pixels inside the flat trian-gles of the rendering model.
Author(s): Juan M. Rius, Daniel Burgos, Angel Cardama
File Type: Journal Paper
Issue:Volume: 13      Number: 3      Year: 1998
Download Link:Click here to download PDF     File Size: 694 KB

Title: ANALYSIS AND DESIGN OF PLANAR WAVEGUIDE SLOT ARRAYS USING SCATTERING MATRIX APPROACH
Abstract: A scattering matrix approach to the analysis and design of planar waveguide slot arrays is described in this paper. The new method employs the scattering matrix for TE10 and TE20 (to the waveguide axis) modes of isolated slot in the broad wall of a rectangular waveguide, rather than the admittance of the slot derived from approximate shunt or series lumped element model for the slot. The method fully accounts for the external mutual coupling due to the TE10 and TE20 modes on the slot, and can be easily extended to include higher order waveguide modes. Fur-thermore, it takes into account the deviation of the slot aper-ture from the sinusoidal distribution that is normally as-sumed with a nearly resonant slot. Numerical results dem-onstrating the viability of the scattering matrix approach, including an example for the design of a 2 x 3 planar array of longitudinal slots, are presented
Author(s): Karthikeyan Mahadevan, Hesham A. Auda, Charles E. Smith
File Type: Journal Paper
Issue:Volume: 13      Number: 3      Year: 1998
Download Link:Click here to download PDF     File Size: 554 KB

Title: EFFICIENT CGM APPLICATION FOR SCATTERING AND RADIATION OF ANTENNAS ON BOARD ARBITRARY STRUCTURES
Abstract: A technique based on an iterative scheme and a current-based method has been developed to determine the scattering and propagation characteristics of arbitrary structures and environments. To obtain a high degree of accuracy, parametric surfaces (NURBS) have been used to model the body surface. The technique solves the MFIE (Magnetic Field Integral Equation) defined over the body surface. The aim of the method is to make the analysis avoiding the memory and CPU time restrictions imposed by low frequency methods such as Method of Moments. Approximate expressions, based on dipole moment formulations, are applied to speed-up the calculations. Two initial guesses for the CGM (Conjugate Gradient Method) have been compared in order to see which one presents the best relationship between convergence and CPU time. Results are presented showing the behavior of the developed methods comparing them with measurements and other electromagnetic methods
Author(s): Olga M. Conde, Manuel F. C
File Type: Journal Paper
Issue:Volume: 13      Number: 3      Year: 1998
Download Link:Click here to download PDF     File Size: 741 KB

Title: FAST FREQUENCY RESPONSE CALCULATIONS OF CAVITY-BACKED APERTURE ANTENNAS USING HYBRID FEM/MOM TECHNIQUE IN CONJUNCTION WITH MODEL BASED PARAMETER ESTIMATION
Abstract: Model Based Parameter Estimation (MBPE) is presented in conjunction with the hybrid Finite Element Method (FEM)/Method of Moments (MoM) technique for fast computation of the input characteristics of cavity-backed aperture antennas over a frequency range. The hybrid FEM/MoM technique is used to form an integro-partial-differential equation to compute the electric field distribution of a cavity-backed aperture antenna. In MBPE, the electric field is expanded as a rational function of two polynomials. The coefficients of the rational function are obtained using the frequency derivatives of the integro-partial-differential equation formed by the hybrid FEM/MoM technique. Using the rational function approximation, the electric field is calculated and the input characteristics of the antenna are obtained over the frequency range. Numerical results for an open coaxial line and a cavity-backed microstrip patch antenna are presented. Good agreement between MBPE and the solutions over individual frequencies is observed. CPU timings for all numerical calculations are presented.
Author(s): C. J. Reddy, , M. D. Deshpande, B. R. Cockrell, F. B. Beck
File Type: Journal Paper
Issue:Volume: 13      Number: 3      Year: 1998
Download Link:Click here to download PDF     File Size: 575 KB

Title: IMPLICITNESS AND STABILITY OF TIME DOMAIN INTEGRAL EQUATION SCATTERING ANALYSES
Abstract: Time domain integral equation analysis of scattering problems has been inhibited by the instability generally observed. Usual treatments are explicit. We here describe an implicit approach, which allows timesteps to be selected to model the temporal variation of the field, rather than being constrained to small values by the need for the wave propagation during a timestep to be less than the smallest nodal spacing. For realistic bodies, this alone can result in computational cost savings by a significant factor. We present an investigation of the stability of the implicit approach, and show that it is much less prone to instability than the explicit. For realistic bodies, with rationally chosen timesteps, the implicit approach is for all practical purposes stable. This is so without recourse to the various temporal averaging schemes which have been proposed for stabilisation of the explicit form.
Author(s): S. J. Dodson, S. P. Walker, M. J. Bluck
File Type: Journal Paper
Issue:Volume: 13      Number: 3      Year: 1998
Download Link:Click here to download PDF     File Size: 778 KB

Title: VALIDATION OF, AND LIMITATIONS ON, THE USE OF NEC-4 FOR RADIATION FROM ANTENNAS BURIED WITHIN A HOMOGENEOUS HALF-SPACE
Abstract: The use of the computer program NEC-4 for the simulation of radiation from buried antennas is considered. NEC-4 uses the “exact” Sommerfield integral formulation for stratified media (in NEC-4, re-stricted to an homogeneous half-space). Although the formulation is rigorous, certain approximations have to be made for numerical implementation. The formu-lation, and some of these issues, is outlined in the paper. Several validation examples comparing results computed using NEC-4 and results available in the lit-erature are presented for antennas buried in various typical media, including ground, fresh water, and the sea. Satisfactory agreement has generally been obtained; where differences have been noted, we have able to explain most in terms of approximate implementa-tion issues.
Author(s): David B. Davidson, H. du Toit Mouton
File Type: Journal Paper
Issue:Volume: 13      Number: 3      Year: 1998
Download Link:Click here to download PDF     File Size: 554 KB