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.

Breast cancer represents one of the main reasons of death among women. As an alternative to the gold standard techniques for breast cancer diagnosis, microwave imaging has been proposed from research community and many microwave systems have been designed mainly to work at low microwave frequencies. Based both on the results of recent dielectric characterization campaigns on human breast ex-vivo tissues up to 50 GHz and on the promising feasibility studies of mm-wave imaging systems, in this article, we propose and test inverse scattering techniques as effective tool to process mm-wave data to image breast cancer. Differently from the radar techniques so far adopted in conjunction with mm-wave imaging system, inverse scattering techniques turn out to be more versatile and robust with respect to the reduction of the number of processed frequencies and eventually also able to characterize the anomaly in terms of electromagnetic properties. In particular, in the above, two image reconstruction techniques, the Linear Sampling Method and the Born Approximation, are proposed and compared against both simulated and experimental data.

A new compressive-sensing-inspired approach is proposed to the detection of faulty radiators in planar antenna arrays from a reduced set of phaseless far-field measurements. In order to deal with whatever kind of arrays, the problem is cast as the recovery of the aperture-field distribution, and two new convex-programming solution procedures are introduced. The first one relies on the improvement of the Total Variation norm technique, while the second one exploits a new aperture field expansion, which allows drastically reducing the number of unknowns of the problem. A wide set of numerical experiments involving benchmark scenarios, as well as full-wave data relative to a realistic antenna, is provided in support of the given theory.

With reference to the mask-constrained power synthesis of shaped beams, we extend the Spectral Factorization method to both uniformly and non-uniformly spaced linear arrays wherein mutual coupling and mounting-platform effects are present. The overall design procedure does not rely on any restriction on the nature and the shape of the fields, and it is cast as a couple of convex optimizations plus a polynomial factorization. Moreover, it allows one to ascertain the actual feasibility of the radiating system before performing the synthesis, and it is able to identify very many different arrayexcitation solutions all corresponding to the desired power pattern. The given theory is supported by numerical experiments concerning the full-wave synthesis of realistic arrays affected by mutual coupling and mounting-platform effects.

A new approach to the design of Graded Artificial Material (GAM)-based devices is proposed by exploiting the inverse scattering framework as a synthesis tool. The introduced general methodology can be applied to arbitrary far-field specifications, thus allowing the design of non-canonical devices. In particular, two different strategies are developed for GAMs based on either graded refractive index (GAMR) or graded filling factor (GAMF). In both strategies, the inverse scattering problem is solved by a proper reformulation of the Contrast Source Inversion method, wherein a proper rescaling of the amplitude of the primary sources is also used. In particular, in the first strategy, the GAMF is obtained by exploiting homogenization theories. In the second strategy, the GAMR is synthesized by exploiting a suitable representation basis for the unknown contrast function, and, then, simple analytical formulas are used to determine the corresponding GAMF. The proposed approach is assessed through the synthesis of an antenna generating a Σ/Δ reconfigurable pattern.

Ground penetrating radar (GPR) technology for underground exploration consists in the transmission of an electromagnetic signal in the ground for sensing the presence of buried objects. While monostatic or bistatic configurations are usually adopted, a limited number of multistatic GPR systems have been proposed in the scientific literature. In this manuscript, we investigate the recovery performance of a specific and unconventional contactless multistatic GPR system, designed at the Georgia Institute of Technology for the subsurface imaging of anti-tank and anti-personnel plastic mines. In particular, for the first time, tomographic approaches are tested against this experimental multistatic GPR system, while most GPR processing in the scientific literature processes multi-monostatic experimental data sets. Firstly, by mimicking the system at hand, an accurate theoretical as well as numerical analysis is performed in order to estimate the data information content and the performance achievable. Two different tomographic linear approaches are adopted, i.e. the linear sampling method (LSM) and the Born approximation (BA) method, this latter enhanced by means of the compressive sensing (CS) theoretical framework. Then, the experimental data provided by the Georgia Institute of Technology are processed by means of a multi-frequency CS and BA-based method, thus generating very accurate 3D maps of the investigated underground scenario.