A space-time discretization criterion for a stable time-marchingsolution of the electric field integral equation

Numerical techniques based on a time-domain recursive solution of the electric field integral equation (EFIE) may exhibit instability phenomena induced by the joint space-time discretization. The above problem is addressed with specific reference to the evaluation of electromagnetic scattering from perfectly conducting bodies of arbitrary shape. We analyze a particular formulation of the method of moments which relies on a triangular-patch geometrical model of the exterior surface of the scattering body and operates according to a “marching-on-in-time” scheme, whereby the surface current distribution at a given time step is recursively evaluated as a function of the current distribution at previous steps. A heuristic stability condition is devised which allows us to define a proper time step, as well as a geometrical discretization criterion, ensuring convergence of the numerical procedure and, therefore, eliminating insurgence of late-time oscillations. The stability condition is discussed and validated by means of a few working examples     

UWB body area network channel modeling: An analytical approach

The aim of this work is to develop an analytically-based approach for ultra wide band (UWB) body area network (BAN) channel modeling. In detail, the body will be modeled as multi-layered stratified cylinders of infinite length, and the Maxwell's equation will be solved for plane wave and line source excitations. Human-type tissues will be assumed in the multi-layered stratified cylindrical model. Validation of the procedure through measurement results has been provided.     

Analysis of Realistic Ultrawideband Indoor Communication Channels by Using an Efficient Ray-Tracing Based Method

A fundamental step in ultrawideband (UWB) communication system design involves the characterization of the indoor propagation channel. In this paper, we show that the UWB propagation channel parameters can be accurately predicted by employing ray tracing (RT) simulation carried out at various frequencies over the signal bandwidth. It is important to note that the determination of the rays reaching a given location is made only once, as the RT algorithm is independent of frequency. A parallel ray approximation (PRA) is used to significantly improve the computational efficiency of the RT based method. Moreover the accuracy of the approximation is verified through a measurement campaign.     

Design of waveguide filters by using genetically optimized frequency selective surfaces

A new optimization procedure suitable for the design of waveguide filters is presented. The filter structure consists of a frequency selective surface (FSS), placed on the transverse plane of a rectangular waveguide, so introducing a filtering behavior of the waveguide. Due to the boundary conditions imposed by the metallic waveguide walls, the FSS results to be infinite in extent, allowing the use of fast and efficient method of moments solvers to analyze its properties. A genetic algorithm (GA) has been adopted to optimize the filter performance. As an application, a waveguide filter has been designed to be used in an easy to fabricate and inexpensive very small aperture terminal (VSAT) feeder, for the ground station of an interactive satellite system.     

Double-loop antenna for wireless tyre pressure monitoring

The design of a double-loop antenna operating at two distinct frequencies is presented for wireless tyre pressure monitoring systems. The radiation properties of the printed antenna, placed inside the wheel and with the tyre rubber, are discussed as well as the performance in terms of gain and power handling.     

Direct GA-based optimisation of resistively loaded wire antennas inthe time domain

An optimisation procedure based on the genetic algorithm is applied to design resistively loaded wire antennas. The broadband characteristic of the antenna is realised through a maximisation of the fidelity factor directly in the time domain. The performance characteristics of the resulting antenna are presented and contrasted with those of the Wu-King design     

Computationally efficient ray-tracing technique for modelling ultrawideband indoor propagation channels

The design and development of high-speed data wireless communication systems within buildings call for the investigation of the ultrawideband indoor propagation channel. To date, ray tracing (RT) based approaches have been widely used to characterise the channel; unfortunately, such techniques, although accurate, turn out computationally intensive. In this work, a parallel ray (PR) approximation is successfully used to significantly improve the computational efficiency of the RT method. The accuracy and the applicability of the proposed approximation are assessed through the analysis of the mean square error between the impulse responses obtained with the PR and the RT methods.     

A novel subgridding scheme based on a combination of thefinite-element and finite-difference time-domain methods

A simple and versatile local mesh refinement scheme, based on the hybridization of the finite-element (FE) and the finite-difference time-domain (FDTD) algorithms, is presented. The scheme achieves considerable flexibility in subgridding by using a transition region between the coarse and fine FDTD grids, meshed according to an unstructured grid, and solved by means of the FE method in the TD. An interpolation scheme in the time domain, which allows the use of different time steps in the coarse and fine mesh regions, is included in the paper     

Evaluation of the electromagnetic field level emitted by medium frequency AM broadcast stations

In order to estimate the level of the electromagnetic field produced by telecommunication systems, different computational techniques can be employed whose complexity depends on the accuracy of the final results. In this paper, we present the validation of a code based on the method of moments that allows us to analyse the electromagnetic field emitted by radio-communication systems operating at medium frequencies. The method is able to provide an accurate estimate of the levels of electromagnetic field produced by this type of device and, consequently, it can be used as a method for verifying the compliance of the system with the safe exposure level regulations and population protection laws. Some numerical and experimental results are shown relevant to an amplitude modulated (AM) radio transmitter, together with the results of a forthcoming system that will be operative in the near future.     

A hybrid FEM-based procedure for the scattering from photoniccrystals illuminated by a Gaussian beam

We provide an efficient numerical procedure for evaluating the field scattered by two-dimensional (2-D) photonic crystals when they are illuminated by Gaussian beams. In particular, the incident Gaussian beam is interpreted as a spectrum of both homogeneous and inhomogeneous plane waves. The scattering of each plane wave is analyzed by resorting to a hybrid technique combining the finite-element method (FEM) with a Floquet modal expansion. Moreover, by applying the standard saddle point method, the evaluation of the field at a specific point of the exterior medium is reduced to the contribution of the fundamental Floquet mode of a single plane wave belonging to the incident spectrum, strongly enhancing the numerical efficiency