Anna Martini

An Innovative Approach Based on a Tree-Searching Algorithm for the Optimal Matching of Independently Optimum Sum and Difference Excitations

An innovative approach for the optimal matching of independently optimum sum and difference patterns through sub-arrayed monopulse linear arrays is presented. By exploiting the relationship between the independently optimal sum and difference excitations, the set of possible solutions is considerably reduced and the synthesis problem is recast as the search of the best solution in a noncomplete binary tree. Towards this end, a fast resolution algorithm that exploits the presence of elements more suitable to change subarray membership is presented. The results of a set of numerical experiments are reported in order to validate the proposed approach pointing out its effectiveness also in comparison with state-of-the-art optimal matching techniques.

An integrated multiscaling strategy based on a particle swarm algorithm for inverse scattering problems

The application of a multiscale strategy integrated with a stochastic technique to the solution of nonlinear inverse scattering problems is presented. The approach allows the explicit and effective handling of many difficulties associated with such problems ranging from ill-conditioning to nonlinearity and false solutions drawback. The choice of a finite dimensional representation for the unknowns, due to the upper bound to the essential dimension of the data, is iteratively accomplished by means of an adaptive multiresolution model, which offers a considerable flexibility for the use of the information on the scattering domain acquired during the iterative steps of the multiscaling process. Even though a suitable representation of the unknowns could limit the local minima problem, the multiresolution strategy is integrated with a customized stochastic optimizer based on the behavior of a particle swarm, which prevents the solution from being trapped into false solutions without a large increasing of the overall computational burden. Selected examples concerned with a two-dimensional microwave imaging problem are presented for illustrating the key features of the integrated stochastic multiscaling strategy.

A Hybrid Approach Based on PSO and Hadamard Difference Sets for the Synthesis of Square Thinned Arrays

A hybrid approach for the synthesis of planar thinned antenna arrays is presented. The proposed solution exploits and combines the most attractive features of a particle swarm algorithm and those of a combinatorial method based on the noncyclic difference sets of Hadamard type. Numerical experiments validate the proposed solution, showing improvements with respect to previous results.

An Innovative Microwave-Imaging Technique for Nondestructive Evaluation: Applications to Civil Structures Monitoring and Biological Bodies Inspection

Industrial and biomedical applications of microwave-imaging techniques based on inverse scattering integral relations become more and more important. In order to reduce computational costs and hence allow a quasi real-time processing, an innovative inversion procedure based on the use of a genetic algorithm and on the Sherman-Morrison-Woodbury matrix inversion method is presented. Selected numerical results concerning various scenarios and scatterer dimensions are presented in order to give some indications on the effectiveness and also current limitations of the proposed approach

Synthesis of Large Monopulse Linear Arrays Through a Tree-Based Optimal Excitations Matching

In this letter, the synthesis of large arrays for monopulse tracking applications is addressed by means of a simple and effective subarraying technique. Towards this purpose, the synthesis problem is recast as the search of an optimal path in a noncomplete binary tree by exploiting some relationships between independently optimal sum and difference excitations. Because of a suitable reduction of the solution space and the implementation of a fast path-searching algorithm, the computational issues arising in dealing with large array aperture are properly addressed. Some numerical experiments are provided in order to assess the feasibility and the computational effectiveness of the tree-based approach.

Ray propagation in nonuniform random lattices

The problem of optical ray propagation in a nonuniform random half-plane lattice is considered. An external source radiates a planar monochromatic wave impinging at an angle theta on a half-plane random grid where each cell can be independently occupied with probability q(j)=1-p(j),j being the row index. The wave undergoes specular reflections on the occupied cells, and the probability of penetrating up to level k inside the lattice is analytically estimated. Numerical experiments validate the proposed approach and show improvement upon previous results that appeared in the literature. Applications are in the field of remote sensing and communications, where estimation of the penetration of electromagnetic waves in disordered media is of interest.

Particle Density Retrieval in Random Media Using a Percolation Model and a Particle Swarm Optimizer

This letter is a first attempt to apply a percolation theory model to the estimation of the density of particles in complex layered two-dimensional media from electromagnetic measurements. A procedure based on an analytical closed-form description of the wave propagation process is presented. The problem is recast as an iterative optimization one and solved by means of a particle swarm optimizer. Numerical experiments show the validity of the proposed solution.

Capacity of wide-band MIMO channels via space-time diversity of scattered fields

In this paper the information capacity of a multiple-input multiple-output (MIMO) Gaussian channel is computed via the theory of non-redundant sampling of scattered fields. Unlike previous works relying on the same approach, it is assumed that communication can occur over a wide frequency band. This leads to a trade-off in the exploitation of diversity, due to the mutual coupling of space and time spectra of the field: maximizing time diversity leads to the impossibility of exploiting space diversity and viceversa. It follows that the ultimate physical capacity limit along both space and time dimensions corresponds either to the maximum achievable information rate of an arbitrarily large MIMO narrowband system, or to the one of a single-input single-output (SISO) ultra-wide band (UWB) system. In contrast, in the practical case of MIMO systems of finite size and finite frequency bands used for communication, space and time diversities can be optimally combined by allocating linearly the signal power in the frequency domain.

Stochastic Ray Propagation in Stratified Random Lattices - Comparative Assessment of Two Mathematical Approaches

In this report, ray propagation in stratified semi-infinite percolation lattices consisting of a succession of uniform density layers is considered. The final version of this article is available at the url of the journal PIER: http://www.jpier.org/PIER/

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.