R. Gomez Martin

Particle-Swarm Optimization in Antenna Design: Optimization of Log-Periodic Dipole Arrays

This paper presents a short tutorial and overview of optimization algorithms based on particle-swarm schemes, and their application to solving electromagnetic problems. As a practical example, a particle-swarm optimization (PSO) tool has been applied in conjunction with the Numerical Electromagnetics Code (NEC) to get the design curves of optimized log-periodic dipole arrays (LPDAs). The graphs show the performance of several radiation parameters (directive gain, front-to-back ratio, bandwidth, SWR, and half-power beamwidth in the E and H planes) as a function of typical design parameters of log-periodic dipole arrays (geometrical parameters and characteristics of the feed). Examples of optimized antennas are given, and their performance is compared to that of standard log-periodic dipole arrays.

Extension of Berenger's absorbing boundary conditions to match dielectric anisotropic media

The authors propose an extension of Berengers perfectly matched layer (PML) absorbing boundary conditions (ABCs) to achieve a perfect matching of waves propagating in anisotropic media. Although the procedure to obtain the matching conditions is valid for any kind of anisotropic material, it has been validated with a lossless two-dimensional uniaxial medium, in which the optical axis is not contained in its plane section. The finite difference time domain method, with an alternative scheme for anisotropic media, is used to simulate the problem and to obtain the numerical reflection coefficient.

A New Hybrid DGTD/FDTD Method in 2-D

In this letter, we present a method to efficiently hybridize the discontinuous Galerkin time domain method (DGTD) with the classical finite difference time domain method (FDTD). The main advantage of this hybrid method is that it maintains the generality of FDTD to treat the main part of a complex inhomogeneous problem, applying only DGTD for accurately taking into account the geometrical details of the objects which would not be properly treated with the usual staircased approximation of the classical FDTD.

GA design of wire pre-fractal antennas and comparison with other Euclidean geometries

A multi-objective genetic algorithm (GA) has been applied in conjunction with the numerical electromagnetic code (NEC) to the optimization of wire pre-fractal Koch-like antennas in terms of bandwidth, efficiency, and electrical size. Their performance is compared to that of other nonfractal designs.

A time-domain near- to far-field transformation for FDTD in two dimensions

This paper proposes an algorithm based on the equi alence principle to calculate, straightforwardly in the time domain, the transient far field response of a two-dimensional structure. The algorithm implementation in ol es the numerical e aluation of a time integral along the nearto far-field con ersion contour of the equi alent currents at the ( ) Huygens surface, obtained with the finite-difference time-domain FDTD method. 2000 John Wiley & Sons, Inc. Microwave Opt Technol Lett 27: 427 432, 2000.

Generalization of Berenger's absorbing boundary conditions for 3-D magnetic and dielectric anisotropic media

A general method is deeloped which extends Berengers () ( ) perfect matching layer PML absorbing boundary conditions ABCs to achiee a perfect matching of waes propagating in 3-D magnetic and r or dielectric anisotropic media. The method isalidated with the finite-difference time-domain method. Q 1998 John Wiley & Sons, Inc. Microwave Opt Technol Lett 18: 126)130, 1998.

A UNIFIED LOOK AT BERENGER'S PML FOR GENERAL ANISOTROPIC MEDIA

The recently proposed general material-independent per- () fectly matched layer GMIPML and extended perfectly matched layer () EPML techniques sere to adapt general dielectric and magnetic anisotropic media. Perfect matching is achieed both by the former, based on a straight generalization of Berengers PML using a D and B formulation, and by the latter using an E and H formulation. In this paper, a general theory enclosing both formulations is proposed. 2001 John Wiley & Sons, Inc. Microwave Opt Technol Lett 28:414 416, 2001.

A Resistively Loaded Thin-Wire Antenna for Mine Detection

This paper shows that, using genetic algorithms to calculate the resistive load distribution along a wire antenna, in order to optimize its broadband characteristics, it is possible to obtain better results in detecting land mines using a GPR, than when the antenna is loaded with the Wu–King resistive profile.

DGTD for a Class of Low-Observable Targets: A Comparison With MoM and (2, 2) FDTD

The simulation of low-observable targets requires high accuracy, both in the geometrical discretization as well as in the numerical solution of the electromagnetic problem. In this letter, we employ the well-known NASA almond to illustrate the accuracy of the leapfrog discontinuous Galerkin method, combined with a local time-stepping algorithm, comparing it to the method of moments (MoM) and the (2, 2) finite-difference time-domain (FDTD) methods.

Time domain optimization of wire antennas loaded with passive linear elements using GA

In this communication Genetic algorithms (GAs) optimizers are applied, directly in the time domain, to the design of broadband thin-wire antennas. The broadband characteristics of the antennas are achieved by loading the wires with combinations of passive loads, trying to maximize the fidelity of the response while keeping the efficiency as high as possible. Multi-objective GAs are used in conjunction with a computer code based on the solution, in the time domain, of the electric field integral equation for wires with arbitrarily connected loads. Representative results are presented.