Andrea Francesco Morabito

On Quantitative Microwave Tomography of Female Breast

Microwave tomography deserves attention in biomedical imaging, owing to its potential capability of providing a morphological and functional assessment of the inspected tissues. However, such a goal requires the not trivial task of solving a non linear inverse scattering problem. In this paper, the factors afiecting the complexity of the inverse problem are exploited to trace guidelines aimed at setting the matching ∞uid, the frequency range and the number of probes in such a way that the dielectric parameters of female breast tissues can be reliably retrieved. Examples, concerning 2D realistic numerical phantoms obtained by NMR images, are given to asses a posteriori the efiectiveness of the proposed guidelines.

Optimal Synthesis of Directivity Constrained Pencil Beams by Means of Circularly Symmetric Aperture Fields

The problem of the optimal synthesis of circularly symmetric aperture distributions able to radiate pencil beams fulfilling well-defined requirements on the far-field and/or the directivity is addressed and solved. In particular, constraints concerning both the sidelobe level (SLL) and the directivity within a coverage zone are dealt with while being careful not to incur into the so called super-directive sources or into aperture fields actually difficult to be realized. The case wherein a constraint is enforced on the dynamics of the excitations is also considered. Numerical examples concerning cases of practical relevance are also shown in support to the given theory.

An Effective Approach to the Synthesis of Phase-Only Reconfigurable Linear Arrays

We present an effective approach to the optimal mask-constrained power pattern synthesis of uniformly spaced array antennas able to dynamically reconfigure their radiation pattern by modifying only the excitation phases. The proposed approach results in a design procedure having a very low computational burden and, by exploiting at best the knowledge available in the separate synthesis of each pattern, is able to solve the underlying combinatorial optimization problem and to achieve solutions close (or equivalent) to the global optimum. A set of representative examples are reported in order to validate the proposed approach. Some extensions of the developed theory to cases other than linear arrays are also outlined.

Optimal Constrained Field Focusing for Hyperthermia Cancer Therapy: a Feasibility Assessment on Realistic Phantoms

Microwave hyperthermia is a non-invasive treatment for cancer which exploits a selective heating of tissues induced through focused electromagnetic flelds. In order to improve the treatments e-ciency, while minimizing side efiects, it is necessary to achieve a constrained focusing of the fleld radiated by the sources. To address this issue, in this paper we present an innovative and computationally efiective approach to the fleld focusing for hyperthermia. The proposed method, after establishing the number of sources to be used, determines the excitations of the given set of sources such to produce a maximum fleld in a given region of space, subject to a completely arbitrary mask for the fleld amplitude in all other regions. As the approach relies on a formulation of the problem in terms of convex programming, it is able to achieve the globally optimal solution without the adoption of computationally intensive global optimization procedures. A preliminary assessment of feasibility is given on hyperthermia therapy of breast cancer by means of numerical examples run on realistic 2D phantoms of female breast.

On the Solution of 2-D Inverse Scattering Problems via Source-Type Integral Equations

With reference to inverse scattering problems, two different integral equation models belonging to the class of source-type integral equations are reviewed, discussed, and properly compared. In particular, starting from the concept of degree of nonlinearity of the scattering problem, universal plots and useful convenience maps are derived and exploited to foresee which is the most convenient integral equation model to adopt for modeling the scattering phenomena at hand. Numerical examples, dealing with both synthetic and experimental data, are reported and discussed. The results fully confirm the theoretical analysis.

A DETERMINISTIC APPROACH TO THE SYNTHESIS OF PENCIL BEAMS THROUGH PLANAR THINNED ARRAYS

This paper presents a simple and innovative deterministic approach to the synthesis of uniformly excited thinned arrays able to fulflll constraints concerning both the sidelobe level and the value of the radiated far fleld (and/or of the directivity) in a set of given directions. Starting from a reference regular (periodic or even aperiodic) lattice and from an optimal continuous reference source fulfllling at best the required speciflcations, the proposed approach flnds out both the number and the location of the isophoric (i.e., equi-amplitude) radiating elements to withdraw in a fast and efiective fashion. In fact, it is based on a deterministic best-fltting procedure which takes inspiration from existing density taper techniques. Examples are provided with reference to the synthesis of large circular arrays and conflrm the interest of the proposed procedure.

Optimal Synthesis of Sum and Difference Patterns With Arbitrary Sidelobes Subject to Common Excitations Constraints

An innovative and computationally effective approach to the synthesis of optimal sum and difference patterns via uniformly spaced arrays with a number of common excitations is presented and assessed. The proposed technique takes advantage from known results in the (separate) optimal synthesis of sum and difference patterns and allows one to manage arbitrary and different bounds concerning both the sidelobe level (SLL) and the beamwidth (BW) of the couple of patterns while sharing part of the feeding network. A set of examples is provided to support the underlying theory and to show potentialities and features of the arising procedure.

DIRECT RADIATING ARRAYS FOR SATELLITE COMMUNICATIONS VIA APERIODIC TILINGS

This paper presents an innovative Direct Radiating Array (DRA) architecture exploiting aperiodic tilings of the plane. In particular, a pinwheel tiling has been selected in order to flx positions of the difierent radiating sources, which are constituted by properly shaped elements. Such a choice allows to achieve a good aperture e-ciency and very low pseudo-grating lobes while using only two difierent kinds of radiating elements. Preliminary results are shown and discussed with reference to both cases wherein the single tiles are not fully populated and wherein ad-hoc sub-array radiators are used. The very encouraging results achieved leave open the way for further interesting possibilities.

An Effective Deterministic Procedure for the Synthesis of Shaped Beams by Means of Uniform-Amplitude Linear Sparse Arrays

A rigorous deterministic approach is proposed for the mask-constrained power pattern synthesis of shaped beams through one-dimensional sparse arrays having uniform-amplitude excitations (and variable phases). The approach includes the well known density taper procedure as a special case. The corresponding technique, which exploits an analytical formulation of the problem and convex programming routines, results in fast computation and is able to achieve optimal solutions without recurring to any global optimization. Numerical results assessing the capabilities of the proposed design method are provided, opening the way to the development of an effective approach for the synthesis of circularly symmetric shaped beams via uniformly-excited circular ring arrays.

ON THE OPTIMAL SYNTHESIS OF RING SYMMETRIC SHAPED PATTERNS BY MEANS OF UNIFORMLY SPACED PLANAR ARRAYS

By taking inspiration from (1), a synthesis strategy is proposed for the case of planar arrays and ring shaped patterns which does not require the exploitation of global optimization procedures. In particular, the approach is able to determine a priori (that is, without solving the overall design problem) whether the given power pattern design constraints can be fulfllled or not, and, in the adflrmative case, to determine the needed excitation coe-cients in a fast deterministic manner. Although the approach does not apply to generic planar arrays and generic constraints, it applies to a large number of problems of actual interest, and outperforms some recently published synthesis procedures. Moreover, it may serve both as a reference solution for more general synthesis procedures, and as an elementary brick for more cumbersome synthesis problems.