T. Isernia

Microwave Imaging of Nonweak Targets via Compressive Sensing and Virtual Experiments

Compressive sensing (CS)-based techniques can represent a very attractive approach to inverse scattering problems. In fact, if the unknown has a sparse representation and the measurements are properly organized, CS allows to considerably reduce the number of measurements and offers the possibility to achieve optimal (or nearly optimal) reconstruction performance. Unfortunately, the inverse scattering problem is nonlinear, while CS theory is well established only for linear recovery problems. As a contribution to overcome this issue, in this letter, we introduce two different CS-inspired approaches that exploit the “virtual experiments” framework, wherein it is possible to cast the inverse scattering problems in a linear form even in the case of nonweak targets.

A Simple Idea for an Effective Sub-Arraying of Large Planar Sources

A suitable deterministic partitioning of large planar arrays in two kinds of properly shaped subarrays is shown to improve performances in terms of side-lobes peaks, directivity and aperture efficiency with respect to other existing solutions. The application of this simple idea to the case of large planar arrays with a reduced number of control points, useful in satellite applications, is demonstrated.

Constrained power focusing of vector fields: an innovative globally optimal strategy

This paper introduces and discusses an innovative approach to focus the electromagnetic power carried by a vector field into a target point, while keeping the field level bounded elsewhere. To overcome the complexity of the underlying NP-hard problem, we introduce a multi-objective optimization framework based on convex programming sub-problems. Notably, such a strategy has the unique capability of achieving the globally optimal solution by means of local search algorithms. A numerical analysis is reported to assess the methods’ performance, including a comparison with previous contributions. The proposed approach is herein presented in the case of 2D vector fields (transverse electric polarization) but it can be easily extended to the general 3D case.

Mask-constrained power synthesis of maximally sparse linear arrays through a compressive-sensing-driven strategy

We propose a new deterministic approach to the synthesis of linear arrays having the least possible number of elements while radiating shaped beams lying in completely arbitrary power masks. The approach takes joint advantage from compressive sensing (CS), from the multiplicity of power patterns lying in a given mask, and from the multiplicity of field solutions corresponding to each of these power patterns. Care is taken in order to exploit the available degrees of freedom in an effective fashion, and in optimizing parameters that affect the CS performance. An extensive numerical comparison against state-of-the-art procedures proves the effectiveness of the approach.

Quasi — Invisibility via inverse scattering techniques

The paper investigates the feasibility of an approach to design effective cloaking devices by means of a joint exploitation of available degree of freedom in synthesis strategies and the physical mechanism underlying cloaking. A different point of view in the design of dielectric covers that minimize the scattering cross section of dielectric objects is introduced and new opportunities are outlined to perform an effective synthesis of cloaking profiles via inverse scattering techniques.

A New Strategy to Constrained Focusing in Unknown Scenarios

We introduce a novel strategy to synthesize an antenna array capable to focus a field in an unknown scenario. The underlying power synthesis problem is efficiently solved via convex programming and using an approximation of the fields radiated by the array elements. This approximation stems from an original exploitation of the equation underlying the Linear Sampling Method. As such, the proposed strategy takes advantage of the broad applicability of this well-known imaging approach. Some numerical examples are given to illustrate the performance of the strategy.

A Compressive-Sensing-Inspired Procedure for Array Antenna Diagnostics by a Small Number of Phaseless Measurements

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.

Microwave tomography of breast cancer: A feasibility study

Medical researches have appointed breast cancer as the primary cause of death in women and early detection as an essential part of effective treatments. X-ray mammography, which is currently the gold-standard method for breast screening, has some limitations hence development of new diagnostic techniques appear of great interest. In the framework of Microwave Tomography, we investigate how the performances of the imaging procedures may be improved by properly acting on the electrical features of the hosting medium and on the working frequencies. Fixed the optimal parameters of the measurement set up, the Contrast Source inversion approach is exploited. Numerical analysis shows that the permittivity profile of the inclusions can be accurately retrieved.

Inverse scattering and compressive sensing as advanced e.m. design tools

In this paper we propose the adoption of the inverse scattering theory for the synthesis of profiles which are able to scatter an imposed scattered field. The design procedure moves from the Contrast Source Inversion (CSI) method. Moreover, by taking inspiration from the ℓ1-norm penalized least square problem, a compressive sensing (CS) inspired inversion scheme is considered for the synthesis of sparse dielectric profiles.

Design of a varying dielectric profile antenna generating reconfigurable Σ — Δ pattern via inverse scattering theory

In this contribution, inverse scattering skills and procedures are exploited to design a dielectric lens antenna able to provide contemporarily some ‘optimal’ sum and delta patterns. Moreover, in order to overcome the fabrication difficulties arising from the need to provide large index gradients in a controlled manner, the effective medium theory is exploited to design a graded photonic crystals (GPCs) structure starting from the synthetized lens.