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Title: Predicting MoM Error Currents by Inverse Application of Residual E-Fields
Abstract: This paper presents a methodology to predict a posterori the error associated with a Method-of-Moments solution. The discussion is limited to a one dimensional pulse basis function wire-based implementation, but is easily extended. A Formulation for Error Prediction based on the relationship between the error in the boundary conditions and the error in the solution is presented, and validated by an over-segmented problem. The formulation is then used in a normally-segmented solution to predict the error by means of a linear interpolation of the calculated current which results in a smoother boundary condition error. The results show that this normally-segmented methodology predicts the error current within 5% of the "accurate" error current obtained by a 20:1 oversegmentation of the problem. Further work needs to be performed to extend this to the multidimensional case, although no technical difficulties are expected with this.
Author(s): A. P.C. Fourie, D. C. Nitch, A.R. Clark
File Type: Journal Paper
Issue:Volume: 14      Number: 3      Year: 1999
Download Link:Click here to download PDF     File Size: 381 KB

Title: On the Iteration of Surface Currents and the Magnetic Field Integral Equation
Abstract: In an effort to mathematically validate the convergence properties of various surface current-iterative methods, the magnetic field integral equation is analyzed for its contraction mapping properties. The analysis is performed first on the general integral operators and then on the matrices representing the discrete forms of the integral operators associated with the different iterative methods. The contraction mapping properties are determined by investigating the spectral radius of each linear operator. Conditions for the verification and validation of these iterative methods are provided, along with mathematical checks for the existence of spurious modes and the existence of internal resonance.
Author(s): D.D. Reuster, G.A. Thiele, P.W. Eloe
File Type: Journal Paper
Issue:Volume: 14      Number: 3      Year: 1999
Download Link:Click here to download PDF     File Size: 583 KB

Title: Modeling of Low-Gain Antennas on Aircraft using APATCH
Abstract: Radiation patterns for low-gain antennas such as those used for telemetry and collision avoidance systems were computed using the APATCH program. APATCH uses shooting and bouncing rays (SBR) to compute the radiation pattern for the antenna intalled on a scattering geometry. A built-in antenna model was used to represent a telemetry antenna and its accuracy verified by comparison with measurements and results from a method of moments patch code. Antenna patterns were computed for various locations on a Cessna 172 and an F-18 Hornet.
Author(s): J. Calusdian, D. Jenn
File Type: Journal Paper
Issue:Volume: 14      Number: 3      Year: 1999
Download Link:Click here to download PDF     File Size: 511 KB

Title: A NOVEL SPATIAL IMAGES TECHNIQUE FOR THE ANALYSIS OF CAVITY BACKED ANTENNAS
Abstract: This paper describes a new contribution to the analysis of arbitrary shielded circuits and antennas of complex shapes, in the frame of the intergal equation (IE) and Method of Moments formulation (MoM). The technique is based on the spatial image approach and a new specially truncated set of images is developed to enhance the convergance behavior of the series involved. Results show that, with the new specially truncated series of images, convergence is achieved very fast. In this paper simulated results obtained with the new approach are compared with measurments.
Author(s): A.A. Melcon, J.R. Mosig
File Type: Journal Paper
Issue:Volume: 14      Number: 3      Year: 1999
Download Link:Click here to download PDF     File Size: 575 KB

Title: EFFICIENT SOLUTION OF LINEAR SYSTEMS IN MICROWAVE NUMERICAL METHODS
Abstract: A common bottle-neck, limiting the performance of many electromagnetic numerical methods, is the solution of sparse linear systems. Until now, this task has been typically solved by using iterative sparse solvers, whose require heavy computational efforts, especially when the problem is not well conditioned. An alternative strategy is based on the use of banded solvers, which numerical complexity is quadratical with respect to the matrix bandwidth. Of course, these methods are efficient provided that the matrix bandwidth is sufficiently small. In this paper, a method (called WBRA) for the bandwith reduction of a sparse matrix is presented: it is here specifically customized to typical electromagnetic matrices. The approach is superior to all the previous algorithims, also with respect to commercial well-known packages, and is suitable also for non-symmetric problems. As demonstrated by results, the use of WBRA, in conjuction with common banded solvers, substantially improves (up to one order of magnitude) the solution times in several electromagnetic approaches, such as Mode-matching, FEM, and MoM analysis of microwave circuits. In conclusion, it is proved that the high efficiency and effectiveness of WBRA turns the stragety of bandwith reduction combined with a banded solver into the most profitable way of solving linear systems in electromagnetic numerical methods.
Author(s): L. Tarricone, F. Malucelli, A. Esposito
File Type: Journal Paper
Issue:Volume: 14      Number: 3      Year: 1999
Download Link:Click here to download PDF     File Size: 625 KB

Title: PARALLEL IMPLEMENTATION OF GALERKIN TECHNIQUE IN LARGE SCALE ELECTROMAGNETIC PROBLEMS
Abstract: An intergal equation formulation in conjunction with a palallelised Galerkin technique is employed to solve large-scale electromagnetic (EM) problems. The proposed technique is applicable to EM structures consisting of similar conducting or dielectric parts, defined as "elements". Coupled intergal equations are derived in the frequency domain, written in terms of the conductivity currents or the electric fields deployed on the conducting or dielectric "elements" surfaces, respectively. The system of intergal equations is numerically solved via the parallel computed Galerkin technique, with convienient entire domain basis functions. Even for ellectrically large structures, the use of entire domain basis functions leads to relatively small order linear systems and the main computational cost refers to the matrix fill rather than the matrix solution. The parallalisation introduced to the computation of the matrix elements overcomes the limitation of using Method of Moments at lower and resonant frequencies. The inherent parallelisim of the introduced technique allows for the results to be obtained with minimal addition to sequental code programming effort. Two indicative electromagnetic compatibility applications are presented, concerning the coulping of incident waves with multiple conducting rectangular plates and the coupling phenomena occuring in a multi-element waveguide array looking into a layered lossy cylinder. Numerical results are presented, while the applicability/suitability of diverse High Performance Computing platforms is judged, based on both performance obtained and ease of code portation.
Author(s): D.I. Kaklamani, K.S. Nikita, A. Marsh
File Type: Journal Paper
Issue:Volume: 14      Number: 3      Year: 1999
Download Link:Click here to download PDF     File Size: 808 KB