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Title: Introduction to Genetic Algorithms in Electromagnetics
Abstract: This special issue of the ACES Journal is devoted to nev developments in Genetic Algorithm (GA) applications in computational electromagnetics. Genetic Algorithms have become extremely popular in the computational electromagnetics literature. The papers included in this special issue are very arcane, so I decided to include an unreviewed tutorial overview at the last minute as an introduction for those of you who are at a more basic level. GAs model natural selection and genetics on a computer to optimize a wide range of problems.
Author(s): Randy L. Haupt
File Type: Journal Paper
Issue:Volume: 15      Number: 2      Year: 2000
Download Link:Click here to download PDF     File Size: 2442 KB

Title: A Genetic Algorithm Optimization Procedure for the Design of Uniformly Excited and Nonuniformly Spaced Broadband Low Sidelobe Arrays
Abstract: This paper presents a systematic methodology for designing uniformly excited broadband low sidelobe linear and planar antenna arrays by varying interelement spacings. In the past, attempts to develop a robust array broadbanding design technique have been only marginally successful because of the large number of possible spacing combinations involved, coupled with the theoretical limitations surrounding the problem. The genetic algorithm (GA) has recently proven to be a very effective design tool for nonuniformly spaced low sidelobe antenna arrays with uniform excitation intended for operation at a single frequency. This paper introduces an approach for extending previous applications of GA to include the design of optimal low sidelobe arrays that operable over a band of frequencies. In addition, it will be demonstrated that designing for low sidelobe operation over a bandwidth adds significant array steerability that can be described as a simple mathematical relation. Finally, it will be shown that the GA objective function is no more complicated to evaluate for broadbanding purposes than it is in the single frequency case. Several examples of GA-designed broadband low sidelobe arrays will be presented and discussed.
Author(s): Brian J. Barbisch, D. H. Werner, P. L. Werner
File Type: Journal Paper
Issue:Volume: 15      Number: 2      Year: 2000
Download Link:Click here to download PDF     File Size: 9470 KB

Title: Application of Evolutionary Optimization Algorithms in Computational Optics
Abstract: The spatial and spectral treatment of electromagnetic fields express an essential operation regarding, e.g., the functionality of dense integrated opitcal devices. Such molding of fields can handly be handled without sophisticated heuristic optimization tools. By means of five design examples we have demonstrated that evolutionary algorithms (EA) are highly qualified to solve "real world" inverse problems considering various applications in the field of planar integrated optics, optical communication technology, and dielectric material modeling as well. In comparison to other optimization schemes Eas are even able to deliver structural and temporal information of the device under optimization which is an important feature when targeting computer guided engineering and virtual design platforms.
Author(s): Dianel Erni, Dorthea Wiesmann, Michael Spuhler, Stephan Hunziker, Esteban Moreno
File Type: Journal Paper
Issue:Volume: 15      Number: 2      Year: 2000
Download Link:Click here to download PDF     File Size: 15956 KB

Title: Genetic-Algorithm Optimization of an Array for Near-Field Plane Wave Generation
Abstract: An alternative approach to the design of an array antenna to be used to generate plane waves in the near field is presented. The original array was designed on the basis of a triangular grid of seven elements arranged in a hexagon, to minimize the number needed to achieve approximately uniform illumination of the test zone, under the assumption of isotropic element radiation patterns. In the alternative approach, a genetic algorithm was used to discover more economical distributions of elements which could still generate acceptable approximations to a plane wave zone. It was found that considerable simplifications from the 'common sense' approach were possible.
Author(s): Neil N. Jackson, Peter S. Excell
File Type: Journal Paper
Issue:Volume: 15      Number: 2      Year: 2000
Download Link:Click here to download PDF     File Size: 9694 KB

Title: Increasing Genetic Algorithm Efficiency for Wire Antenna Design Using Clustering
Abstract: The Genetic Algorithm (GA) is a very robust, powerful technique that is capable of optimizing designs in a very multimodal search spaces. However, it also requires significant numbers of simulations to perform such optimizations. If the simulations are expensive, as in the case of antenna design, GA's can be prohibitively expensive to use. A clustering technique has been investigated which cuts the required number of function calls 20-90% with minor or no degredation in the optimization quality. In this technique, a GA using real-valued genes is halted when the population has clustered around portions of the search space, and a local optimization technique completes the optimization quickly. This method has been applied to a variety of test functions and wire antenna designs, and the advantages of this technique seem to have broad applicability.
Author(s): D.S. Linden, R. MacMillan
File Type: Journal Paper
Issue:Volume: 15      Number: 2      Year: 2000
Download Link:Click here to download PDF     File Size: 7012 KB

Title: Optimum Population Size and Mutation Rate for a Simple Real Genetic Algorithm that Optimizes Array Factors
Abstract: The population size and mutation rate of a genetic algorithm have great influence upon the speed of convergence. Most genetic algorithm enthusiants use a large population size and low mutation rate due to the recommendations of several early studies. These studies were somewhat limited. This paper presents results that show a small population size and high mutation rate are actually better for many problems.
Author(s): Randy L. Haupt, Sue Ellen Haupt
File Type: Journal Paper
Issue:Volume: 15      Number: 2      Year: 2000
Download Link:Click here to download PDF     File Size: 9141 KB

Title: A Genetic Approach for the Efficient Numerical Analysis of Microwave Circuits
Abstract: The development of effiecient and effective algoritms for sparse matrix bandwidth minimization is of paramount importance for the enhancement of many numerical techinques for the analysis of microwave circuits. The tast of bandwidth reduction is computationally hard. Several approaches have already been proposed, but the problem is still open. In this paper, a genetic solution is proposed. The genetic algorithm is described, as well as its main characteristics (choice of chromosomes, genetic operations, etc.). Results demonstrate that the advantages of the genetic approach vanish because of the huge computational effort required. This severe limitation is removed thanks to the natural amenability of genetic algorithms to a parallel implementation. Results in the paper prove that a parallel genetic approach is a state-of-the-art solution to the problem of bandwidth reduction of sparse matrices encountered in electromagnetic numerical methods.
Author(s): Luciano Tarricone
File Type: Journal Paper
Issue:Volume: 15      Number: 2      Year: 2000
Download Link:Click here to download PDF     File Size: 6607 KB

Title: The application of nested dissection to the solution of a 2.5D electromagnetic problem
Abstract: We use the method of nested dissection to solve a 2.5D finite difference electromagnetic problem. This method is considered in some detail, and we have found that the expected theoretical run time savings over more common methods are realised in practice. The program has been used to model EM propagation in coal seams with a view to detecting seam disruptions, which can cause a loss of production in longwall mining operations. Various experimental results and a field survey are discuessed and we are able to use these results to construct a physically reasonable model which explanes the field data. Some further realistic geological structures are modelled and a comparison between out modelling program and several independent methods show satisfactory agreement.
Author(s): G.H. Smith, P.R. Williamson, K. Vozoff
File Type: Journal Paper
Issue:Volume: 15      Number: 2      Year: 2000
Download Link:Click here to download PDF     File Size: 1193 KB

Title: A Novel Preconditioning Technique and Comparison of Three Formulations for Hybrid FEM/MoM Methods
Abstract: Hybrid FEM/MoM methods combine the finite element method (FEM) and the method of moments (MoM) to model inhomogenous unbounded problems. These two methods are coupled by enforcing field continuity on the boundary that seperates the FEM and MoM regions. There are three ways of formulating hybrid FEM/MoM methods: outward-looking formulations, inward-looking formulations and combined formulations. In this paper, the three formulations are compared in terms of computer-resource requirements and stability and four sample problem geometries. A novel preconditioning technique is developed for the outward-looking formulation. This technique greatly improves the convergence rate of iterative solvers for the type of problems investigated in this study.
Author(s): Yun Ji, Hao Wang, Todd H. Hubing
File Type: Journal Paper
Issue:Volume: 15      Number: 2      Year: 2000
Download Link:Click here to download PDF     File Size: 9403 KB

Title: A New Excitation Model For Probe-Fed Printed Antenna On Finite Size Ground Planes
Abstract: This paper presents a new excitation model for probe-fed printed antennas on both infinite and finite size ground planes. The model has been developed within the general frame of the mixed potential integral equation (MPIE) and the method of moments (MoM). The technique is based on a delta-gap voltage model, and a special procedure is implemented inside the integral equation to effecitivly impose a voltage reference plane into a floating metallic plate which is acting as a ground plane. The present technique allows the accurate calculation of the input impedance of printed antennas, and the effects of finite size ground planes can be easily accounted for in the calculations. In addition, an efficient technique is present for the evaluation of the radiation patterns of printed antennas, taking also into account the presence of the finite size ground plane. Comparisons with measured results show that the new derived excitation method is indeed accurate, and can be used for the prediction of the backside radiation and sidelobe levels of real life finite ground plane printed antennas.
Author(s): F. Tiezzi, A. Alvarez-Melcon, Juan R. Mosig
File Type: Journal Paper
Issue:Volume: 15      Number: 2      Year: 2000
Download Link:Click here to download PDF     File Size: 5422 KB