This paper presents a tutorial and overview of genetic algorithms for electromagnetic optimization. Genetic-algorithm (GA) optimizers are robust, stochastic search methods modeled on the concepts of natural selection and evolution. The relationship between traditional optimization techniques and the GA is discussed. Step-by-step implementation aspects of the GA are detailed, through an example with the objective of providing useful guidelines for the potential user. Extensive use is made of sidebars and graphical presentation to facilitate understanding. The tutorial is followed by a discussion of several electromagnetic applications in which the GA has proven useful. The applications discussed include the design of lightweight, broadband microwave absorbers, the reduction of array sidelobes in thinned arrays, the design of shaped-beam antenna arrays, the extraction of natural resonance modes of radar targets from backscattered response data, and the design of broadband patch antennas. Genetic-algorithm optimization is shown to be suitable for optimizing a broad class of problems of interest to the electromagnetic community. A comprehensive list of key references, organized by application category, is also provided.

Genetic algorithms in engineering electromagnetics

Genetic algorithms are on the rise in electromagnetics as design tools and problem solvers because of their versatility and ability to optimize in complex multimodal search spaces. This paper describes the basic genetic algorithm and recounts its history in the electromagnetics literature. Also, the application of advanced genetic operators to the field of electromagnetics is described, and design results are presented for a number of different applications.

Genetic algorithm optimization applied to electromagnetics: a review

Preface 1. Introduction 2. FDTD Method for periodic structure analysis 3. EBG Characterizations and classifications 4. Design and optimizations of EBG structures 5. Patch antennas with EBG structures 6. Low profile wire antennas on EBG surfaces 7. Surface wave antennas Appendix: EBG literature review.

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Electromagnetic Band Gap Structures in Antenna Engineering

This paper focuses on interacting particle systems methods for solving numerically a class of Feynman-Kac formulae arising in the study of certain parabolic differential equations, physics, biology, evolutionary computing, nonlinear filtering and elsewhere. We have tried to give an “expose” of the mathematical theory that is useful for analyzing the convergence of such genetic-type and particle approximating models including law of large numbers, large deviations principles, fluctuations and empirical process theory as well as semigroup techniques and limit theorems for processes.

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Branching and interacting particle systems. Approximations of Feynman-Kac formulae with applications to non-linear filtering

This paper describes a class of linear thinned arrays with predictable and well-behaved sidelobes. The element placement is based on almost difference sets and the array power pattern is forced to pass through N uniformly-spaced values that, although neither equal nor constant as for difference sets, are a-priori known from the knowledge of the aperture size, the number of active array elements K, and the features of the correlation function. Such a property allows one to predict the bounds of the confidence range of the peak sidelobe of the admissible arrays obtainable through simple shift operations on a binary sequence. The expected peak sidelobe performances turn out to be comparable with those from difference sets, even though obtainable in a wider set of array configurations, and improved in comparison with cut-and-try random-placements.

/pdf/linear-array-thinning-exploiting-almost-difference-sets-4gsbk6k7wp.pdf

Linear Array Thinning Exploiting Almost Difference Sets

Constraining equations for the reflection coefficient of any arbitrary periodic surface of infinitesimal thickness is presented. These constraints can help verify the accuracy of the numerical results and give further insight into the FSS. The constraints allow shoe that there is a theoretical limit on the amount of energy that can be lost. The analysis presented can be extended to any number of substrates and superstrates but it cannot be extended to multiple periodic surfaces. The field scattered from the FSS is a summation of plane waves (called Floquet modes) that satisfy the periodic boundary condition. The Floquet modes are also orthogonal to each other. As a result, the total power is the sum of the power in each Floquet mode. In addition, each Floquet mode must independently satisfy the electric and magnetic field boundary conditions. We therefore enforce the boundary conditions only on the lowest order Floquet mode (that is the mode that propagates along the specular direction).

Analysis of arbitrary frequency selective surfaces: analytic constraints

Previous findings show that frequency selective surfaces (FSS) can have resonances of arbitrarily narrow bandwidths. The reason why the bandwidth of certain resonances is necessarily very narrow is shown. We prove that if the current distribution at resonance is mostly odd, then the current magnitude must approach infinity when the angle of incidence approaches normal (0/spl deg/). Since infinite currents cannot physically exist, the resonant bandwidth must approach 0/spl deg/ in order to suppress the infinite currents.

Bandwidth properties of odd mode resonances in frequency selective surfaces

The increasing interest in the deployment of satellite constellations for personal communications has motivated the study of handset-mounted dual-mode antennas capable of operating in terrestrial- and satellite-based systems. These antennas must remain compact for handset operation, resonate at the proper frequencies, and provide the proper polarization (circular for satellite and linear for terrestrial operation). Additionally, in order to fully understand the antenna performance, it is necessary to predict the effect of the operator's human tissue on the antenna radiation characteristics. This paper presents a dual-mode antenna consisting of a circularly polarized (CP) microstrip patch element and a linearly polarized (LP) planar inverted-F antenna (PIFA). The CP microstrip patch operates at the satellite up-link (1610 to 1626.5 MHz) and down-link (2483.5 to 2500 MHz) bands and the LP PIFA operates at the terrestrial band (902 to 928 MHz). The finite-difference time-domain technique (FDTD) is used to simulate the antenna with and without the presence of biological tissue. The influence of deploying the antenna away from the tissue is also discussed and simulation results show the improvement in performance obtainable using this strategy.

Dual-mode antenna for satellite/terrestrial communications

Time-domain differential equation solvers, such as the finite-difference and finite-volume time-domain (FDTD and FVTD) algorithms, are receiving considerable attention as viable solution techniques for complex radiation and scattering problems. These techniques arise from using discrete approximations to the calculus operators in Maxwell's time-domain equations. However, despite the similarities between these two algorithms, they are surprisingly different in their formulations, their implementations, and most importantly their domains of applicability. This paper compares these methodologies in terms of their development and capabilities. Numerical examples are used to demonstrate their relative accuracy and computational requirements for different problems. A novel hybrid technique which builds upon the modeling strengths of each algorithm is also proposed and demonstrated through representative numerical examples.

Finite-difference and finite-volume time-domain techniques: comparison and hybridization

In this paper we solve for the scattered field from a periodic surface, which is usually referred as a frequency selective surface (FSS). Due to inherent discontinuities in the derivative of the scattered field as a function of frequency, the condition number increases without bound. Even though the condition number is extremely high (>10/sup 15/), the solution of the scattered field is very accurate.

Y. Rahmat Samii

Papers

Analysis of arbitrary frequency selective surfaces: analytic constraints

Bandwidth properties of odd mode resonances in frequency selective surfaces

Dual-mode antenna for satellite/terrestrial communications

Finite-difference and finite-volume time-domain techniques: comparison and hybridization

Examples of ill-conditioned matrices where simple inversion yields satisfactory results