Amelia Rubio Bretones

Transient excitation of a straight thin-wire segment: a new look at an old problem

The transient excitation of a straight thin-wire segment is analyzed with the aid of a one-dimensional integral equation for the current along the wire. An almost exact derivation of that equation, in which only the radial current on the end faces is approximated, is given. The integral equation obtained turns out to be identical to the reduced version of Pocklingtons equation. On the basis of this derivation, existing and new numerical solution techniques are critically reviewed. Pocklingtons equation and Hallens equivalent form are solved directly by marching on in time as well as indirectly via a transformation to the frequency domain. For Pocklingtons equation, a conventional moment-method discretization leads to a Toeplitz matrix that is inverted with Levinsons algorithm. For Hallens equation, the Toeplitz structure is disturbed, and the frequency-domain constituents are determined with the aid of the conjugate-gradient-FFT method. Illustrative numerical results are presented and discussed. >

Time-domain integral equation methods for transient analysis

Some recent developments and extensions of the method of moments for analyzing, in the time domain, the interaction of transient electromagnetic waves with perfect electric conductors are described. The electric and magnetic time-domain integral equations (TDIEs) are formulated and their characteristics briefly discussed. Some issues involved in the formulation and solution of the thin-wire electric-field integral equation are examined. The solution of the magnetic- and electric-field integral equations for bodies modeled by patches is considered. The problem of the instabilities that appear in the solution of the TDIEs is addressed. The possibilities of using postprocessing of the time-domain data to visualize the history of electromagnetic phenomena are illustrated.<<ETX>>

Extension of the ADI-FDTD method to Debye media

This paper describes an extension of the alternating direction implicit finite-difference time-domain (ADI-FDTD) method to analyze problems involving Debye media.

A hybrid time-domain technique that combines the finite element, finite difference and method of moment techniques to solve complex electromagnetic problems

This paper describes a hybrid technique directly operating in time domain that combines the finite element time domain (FETD), the finite-difference time-domain (FDTD) and the integral-equation-based method of moments in the time domain (MoMTD) techniques to analyze complex electromagnetic problems involving thin-wire antennas radiating in the presence of inhomogeneous dielectric bodies whose shape can be arbitrary. The method brings together the ability of the FDTD scheme to deal with arbitrary material properties, the versatility of the FETD to accurately model curved geometries, and that of the MoM to analyze thin-wire structures. Working in the time domain provides wide-band information from a single execution of the marching-on-in-time procedure and simplifies the interfacing of the FE and MoM methods with the FDTD, an approach specifically designed for time domain analysis. Numerical results that validate the hybrid method and show its capabilities are presented in the paper.

GA design of a thin-wire bow-tie antenna for GPR applications

A microgenetic algorithm has been applied to design a new ultrawideband thin-wire bow-tie antenna for ground-penetrating radar applications. The broadband performance of the antenna is achieved by resistive loading and by optimizing the number of wires and the angular distances between those wires. The radiation characteristics of the optimized antenna are discussed, and its performance is compared to that of a resistively loaded Wu-King dipole.

Benchmark Antenna Problems for Evolutionary Optimization Algorithms

A set of antenna-optimization problems is presented that satisfies the necessary requirements to form a test suite useful for measuring and comparing the performance of different evolutionary optimization algorithms (EAs) when they are applied to solve complex electromagnetic problems. The ability of the proposed test suite to find strong and weak points of any EA is illustrated by a complete study of four broadly used evolutionary algorithms carried out with the aid of the new test functions

Some thoughts about transient radiation by straight thin wires

The paper discusses, from a physical point of view, several basic features related to the transient radiation of electromagnetic waves by straight thin-wire antennas.

On the dispersion relation of ADI-FDTD

In this letter, we analyze the alternating direction implicit finite-difference time-domain (ADI-FDTD) dispersion relation and find the numerical plane-wave relationship between the magnetic and electric fields, showing that the scheme is not divergence-free. We also show that negative-group-velocity modes with positive phase velocities may appear for high Courant numbers. A parallel comparison is made with the behavior of the classical Yee FDTD and the Crank-Nicolson schemes.

A novel frequency agile beam scanning reconfigurable antenna

A new and novel design methodology is introduced for a frequency agile planar reconfigurable antenna capable of 360/spl deg/ beam scanning in the azimuthal plane. The versatility of the reconfigurable antenna is demonstrated through several design examples. A similar approach is then used to design a volumetric antenna which is capable of beam steering in three dimensions. Tuning of both 2D and 3D reconfigurable antenna designs is accomplished by means of variable capacitors, whose values are determined via a genetic algorithm optimization process.

A Hybrid Genetic-Algorithm Space-Mapping Tool for the Optimization of Antennas

A hybrid global-local optimization technique for the design of antennas is presented. It consists of the subsequent application of a genetic algorithm (GA) that employs coarse models in the simulations and a space mapping (SM) that refines the solution found in the previous stage. The technique is particularly suited to optimization problems for which long computational times are required to achieve accurate solutions