Quad-band patch antenna for Galileo and Wi-Max services

The design of a patch antenna working in E5-L1 Galileo, 2.5 and 3.5 GHz Wi-Max bands is discussed. Starting from a classical rectangular patch antenna with four resonant modes located around the required spectrum regions, the tuning of the operating frequencies is obtained by perturbing the perimeter of the antenna shape according to a pre-fractal Koch-like erosion process. To show the effectiveness and reliability of the synthesised structure, a selected set of numerical and experimental results are reported and discussed.     

Experimental validation of fully-adaptive smart antenna prototype

The architecture of a fully-adaptive smart antenna working in the 2.4 GHz band is described and its functionalities preliminarily assessed. The radiating unity consists of an eight-element linear array of dipoles with a finite reflecting plane. The adaptive behaviour is achieved by means of a set of electronically-driven vector modulators that realise the array weights. The capability to react in real-time to complex interference scenarios is provided by an SW control module based on the particle swarm optimiser (PSO) algorithm. To assess the effectiveness of such an implementation, a selected set of results is reported and discussed.     

A 3-GHz microwave imaging system based on a modulated scattering technique and on a modified Born approximation

This article deals with short-range active microwave imaging. In particular, a 3-GHz imaging system based on a modulated scattering technique is described. By using a probe made of an array of (passive) dipoles rotating around a test area, it is possible to measure the field scattered by a long cylinder under approximately transverse-magnetic illumination conditions. Moreover, some considerations are made concerning the relationship for the modulated scattering techniques. Finally, some preliminary experimental results are presented. They were obtained by using a numerical approach to the electromagnetic inverse scattering problem which is developed in the spatial domain, and by making use of a modified Born approximation. © 1998 John Wiley & Sons, Inc. Int J Imaging Syst Technol, 9, 395–403, 1998     

New results on electromagnetic imaging based on the inversion of synthetic and measured scattered-field data

A new approach for the inversion of synthetic and measured scattered data is proposed in this paper. The approach is based on an iterative technique in which the nonlinear equations of the inverse-scattering problem are solved within the pth-order Born approximation. A regularization scheme based on an inexact-Newton method is applied. Several numerical simulations and experimental results are reported. Multiple separated dielectric cylinders are localized and reconstructed in a noisy environment.     

A circuital approach to evaluating the electromagnetic field on rectangular apertures backed by rectangular cavities

In this paper, the problem of evaluating the electromagnetic field on rectangular apertures backed by rectangular cavities is investigated. The electromagnetic-field distribution is derived by using a circuital model of an aperture and suitable forcing terms introduced into the equations related to the aperture model. The effects of a rectangular cavity on the aperture-field distribution are assessed by considering the rectangular cavity as a load impedance. The impedance value is obtained by modeling the rectangular cavity as a length of rectangular waveguide back-ended by a short. The distribution of the electromagnetic field on the aperture is used as an exciting source to evaluate, through a modal expansion, the electromagnetic field inside the cavity. Numerical simulations are in a good agreement with both other theoretical models and experimental data.     

Ray propagation in nonuniform random lattices. Part II

In this paper and its companion [J. Opt. Soc. Am. A.23, 2251 (2006)], the problem of ray propagation in nonuniform random half-plane lattices is considered. Cells can be independently occupied according to a density profile that depends on the lattice depth. An electromagnetic source external to the lattice radiates a monochromatic plane wave that undergoes specular reflections on the occupied sites. The probability of penetrating up to level k inside the lattice is analytically evaluated using two different approaches, the former applying the theory of Markov chains (Markov approach) and the latter using the theory of Martingale random processes (Martingale approach). The full theory concerned with the Martingale approach is presented here, along with an innovative modification that leads to some improved results. Numerical validation shows that it outperforms the Markov approach when dealing with ray propagation in dense lattices described by a slowly varying density profile.     

Spline-shaped ultra-wideband antenna operating in ecc released frequency spectrum

A spline-shaped antenna for ultra-wideband communications that operates in the Electronic Communications Committee (ECC) released band from 6 up to 8.5 GHz is described. Selected simulated and measured data are reported to assess the achieved impedance matching over the whole band of interest and the distortionless behaviour, as well as to show the omnidirectional radiation properties.     

Design of miniaturised ISM-band fractal antenna

Miniaturisation techniques for antenna designs based on fractal geometries are of growing interest in wireless communications. Described is the design of a miniaturised fractal antenna prototype. To this end, a particle swarm optimiser is used to optimise simultaneously the fractal shape and the input impedance by acting on the thickness of the antenna segments to avoid matching networks. The effectiveness of the approach is confirmed by simulated and experimental results.     

Automatic design and optimisation of EMI filter using commercially-available components

Designing customised EMI filters is a challenging task since the choice of the circuit topology as well as of the discrete values of the electric components, for satisfying multiple electrical requirements, is not trivial and no standard guidelines are available. An approach based on a particle swarm optimiser, used in conjunction with a circuital simulator, is described. By using equivalent models of commercial components, such a method allows the synthesis of reliable and ready-to-build filters. As an example, a filter prototype is realised and its efficiency is assessed through numerical and experimental evaluations     

An innovative computational approach based on a particle swarm strategy for adaptive phased-arrays control

In this paper a new approach to the control of phased arrays is presented and assessed. Starting from the adaptive array theory, a particle swarm strategy is used to tune the phase coefficients of the array in order to adaptively minimize/avoid the effects of interfering signals at the receiver. To show the effectiveness of the proposed approach, a selected set of numerical examples, concerned with linear as well as planar arrays, is presented. Furthermore, to evaluate the advantages of the particle swarm optimizer (PSO)-based strategy over state-of-art methods, a comparative study is carried out by analyzing the performance of the method in terms of both the signal-to-interference-plus-noise-ratio and resulting beam pattern. The achieved results, even though preliminary, seem to confirm that the PSO-based approach satisfactorily works and it generally outperforms previously proposed/state-of-art phase-only adaptive control strategies.