Challenges in Computational Electromagnetics:Analysis and Optimization of Planar Multilayered Structures

To meet strict requirements of the information society technologies, antennas and circuit elements are becoming increasingly complex. Frequently, their electromagnetic (EM) properties cannot be anymore expressed in closed-form analytical expressions mainly because of the multitude of irregular geometries found in actual devices. Therefore, accurate and efficient (in terms of computational time and memory) electromagnetic models coupled with the robust optimization techniques, are needed in order to be able to predict and optimize the behavior of the innovative antennas in complex environments. The contribution of this thesis consists in the development and improvement of accurate electromagnetic modeling and optimization algorithms for an ubiquitous class of antennas, the planar printed antennas. The approach most commonly used to model and analyze this type of structures is the Integral Equation (IE) technique numerically solved using the Method of Moments (MoM). From the computational point of view, the main challenge is to develop techniques for efficient numerical evaluation of spatial-domain Green's functions, which are commonly expressed in terms of the well-known Sommerfeld integrals (SIs), i.e., semi-infinite range integrals with Bessel function kernels. Generally, the analytical solution of the SIs is not available, and their numerical evaluation is notoriously difficult and time-consuming because the integrands are both oscillatory and slowly decaying, and might possess singularities on and/or near the integration path. Due to the key role that SIs play in many EM problems, the development of fast and accurate techniques for their evaluation is of paramount relevance. This problem is studied in detail and several efficient methods are developed. Finally, the applicability of one of these methods, namely the Weighted Averages (WA) technique, is extended to the challenging case appearing in many practical EM problems: the evaluation of semi-infinite integrals involving products of Bessel functions. However, the development of effective analysis codes is only one aspect. At least equally important is the availability of reliable optimization techniques for an adequate design of antennas. For that purpose, the Particle Swarm Optimization (PSO) algorithm is introduced in the context of our analysis codes. Moreover, the innovative hybrid version of the PSO algorithm, called the Tournament Selection PSO, has been proposed with the aim of even further improving convergence performances of the classical PSO algorithm. Detailed theoretical description of this socially inspired evolutionary algorithm is given in the thesis. Finally, the characteristics of both algorithms are compared throughout several EM optimization problems

Can Tournament Selection Improve Performances of the Classical Particle Swarm Optimization Algorithm?

Abstract — Particle Swarm Optimization (PSO) algorithm is known to be very efficient solution for electromagnetic (EM) optimization problems. In this paper we show that binary tournament selection applied to PSO algorithm further speedsup its convergence. Having in mind that EM simulation is the most time-consuming part of the optimization, reducing the overal number of iterations (EM solver calls) is of a paramount relevance. I

Spherical Lens Antenna Designs with Particle Swarm Optimization

WOSInternational audienceA design procedure for spherical lens antennas is described. A particle swarm optimization (PSO) algorithm is coupled to a mode matching technique based on spherical wave expansion to analyze the lens antennas. The proposed methodology is applied to three optimization problems using real-number and binary PSO. First, the maximization of the directivity of Luneburg lens antennas is addressed. Then, amplitude shaped radiation patterns are synthesized by optimizing both amplitude and position of each element of an array that illuminates a lens. Finally, a dual-beam reconfigurable lens antenna is optimized. By only switching properly the elements of an array, the lens antenna radiates either a directive or a sectoral beam. Numerical comparisons with a full wave commercial software successfully validate the proposed design procedure

Numerical integration of Sommerfeld integrals based on singularity extraction techniques and double exponential-type quadrature formulas

A direct integration algorithm for the evaluation of Sommerfeld integrals is presented. This algorithm does not require the deformation of the integration path to avoid spectral singularities. The integration is performed along the real axis only. The algorithm is based on the combination of an asymptotic extraction technique to remove the singularities and double-exponential quadrature rules to take the tail of the integral into account. Numerical examples confirm the validity of the proposed algorithm

KUL and EPFL cooperation on numerical integration of Sommerfeld integrals.

This paper reports the result of the cooperation between KUL and EPFL on the numerical integration of Sommerfeld integrals (SI). Each institution is well-known for developing specific techniques suited for the evaluation of SI: double-exponential quadrature rules to take the tail of the integral into account (EPFL) and an asymptotic extraction technique to remove the singularities (KUL). The combination of these two techniques results in a very promising algorithm, allowing to perform the integration along the real axis only. Several examples illustrate the algorithm efficiency