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.

In this article, we propose a method based on the aperture antennas theory to understand the limitations of orbital angular momentum (OAM) antennas in far-field links. Additional insight is also given by analyzing the properties of the operators relating source and farfield distributions for a given order of the vortex and emphasizing additional drawbacks. The degrees-of-freedom (DoF) of the fields associated with the different orders of the vortices are also discussed.

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.

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.

A new approach to array antenna diagnostics by means of amplitude-only far-field measurements is proposed. The procedure takes advantage from the compressive sensing theory and is able to deal with linear, planar, and conformal fixed-geometry arrays. In the case of low faulty element percentages, the overall problem is reduced to a convex programming optimization. The minimum number of measurements allowing the success of recovery of either real or complex excitations is identified through an extensive set of numerical results. Interesting outcomes concerning the impact of the noise on measured data, the criterion adopted to choose the measurement points, and the trivial ambiguities inherent to the solution of phase retrieval problems are also provided.

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.