A. Rubio Bretones

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.

Source and Boundary Implementation in Vector and Scalar DGTD

We summarize the boundary and source implementation for the several formulations of the discontinuous Galerkin time domain method (DGTD). Since DGTD with zeroth-order scalar basis functions using the upwind flux, coincides with the finite volume time domain (FVTD), many of the concepts developed for FVTD can be ported to DGTD in any of its different formulations (scalar/vector basis, upwind/centered flux). Numerical examples illustrate the different alternatives.

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.

Time domain analysis of thin-wire antennas over lossy ground using the reflection-coefficient approximation

This paper presents a procedure to extend the methods of moments in time domain for the transient analysis of thin-wire antennas to include those cases where the antennas are located over a lossy half-space. This extended technique is based on the reflection coefficient (RC) approach, which approximates the fields incident on the ground interface as plane waves and calculates the time domain RC using the inverse Fourier transform of Fresnel equations. The implementation presented in this paper uses general expressions for the RC which extend its range of applicability to lossy grounds, and is proven to be accurate and fast for antennas located not too near to the ground. The resulting general purpose procedure, able to treat arbitrarily oriented thin-wire antennas, is appropriate for all kind of half-spaces, including lossy cases, and it has turned out to be as computationally fast solving the problem of an arbitrary ground as dealing with a perfect electric conductor ground plane. Results show a numerical validation of the method for different half-spaces, paying special attention to the influence of the antenna to ground distance in the accuracy of the results.

An Analysis of the Leap-Frog Discontinuous Galerkin Method for Maxwell's Equations

In this paper, we explore the accuracy limits of a finite-element time-domain (TD) method applied to the Maxwell equations, based on a discontinuous Galerkin scheme in space, and a leap-frog temporal integration. The dispersion and dissipation properties of the method are investigated, as well as the anisotropy of the errors. The results of this novel analysis are represented in a practical and comprehensible manner, useful for the application of the method, and for the understanding of the behavior of the errors in discontinuous Gelerkin TD methods. A comparison with the finite-difference TD method, in terms of computational cost, is also included.

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.

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.

A New Efficient and Stable 3D Conformal FDTD

A novel conformal technique for the FDTD method, here referred to as Conformal Relaxed Dey-Mittra method, is proposed and assessed in this letter. This technique helps avoid local time-step restrictions caused by irregular cells, thereby improving the global stability criterion of the original Dey-Mittra method. The approach retains a second-order spatial convergence. A numerical experiment based on the NASA almond has been chosen to show the improvement in accuracy and computational performance of the proposed method.

Multiobjective-Optimized Design of a New UWB Antenna for UWB Applications

A multiobjective genetic algorithm has been applied to design a new printed, bow-tie antenna for ultrawideband applications, that is, ground penetrating radar, short range and high data rate communications, and so forth. The ultrawideband performance with respect to antenna impedance and gain is achieved by an optimized resistive loading profile and flare angle. A low-cost prototype is manufactured and numerical simulations are validated with measurements.