Lorenzo Poli

Handling Sideband Radiations in Time-Modulated Arrays Through Particle Swarm Optimization

The minimization of the power losses in time-modulated arrays is addressed by means of a suitable strategy based on particle swarm optimization. By properly modifying the modulation sequence, the method is aimed at reducing the amount of wasted power, analytically computed through a very effective closed-form relationship, while constraining the radiation pattern at the carrier frequency below a fixed sidelobe level. Representative results are reported and compared with previously published solutions to assess the effectiveness of the proposed approach.

Harmonic Beamforming in Time-Modulated Linear Arrays

In this paper, the synthesis of simultaneous multibeams through time-modulated linear arrays is studied. Unlike classical phased arrays where the antenna aperture is usually shared to generate multiple beams, the periodic on-off sequences controlling the static excitations are properly defined by means of an optimization strategy based on the Particle Swarm algorithm to afford desired multiple patterns at harmonic frequencies to make practical application of these harmonic beams which are typically regarded as an undesirable effect in time-modulated arrays. The synthesis of simultaneous broadside sum and difference patterns, flat-top and narrow beam patterns, and steered multibeams is enabled as assessed by a set of selected results reported and discussed to show the potentialities of the proposed method. Comparisons with previously published results are reported, as well.

Microwave Imaging Within the First-Order Born Approximation by Means of the Contrast-Field Bayesian Compressive Sensing

A new approach based the contrast field (CF) formulation of the microwave imaging problem that exploits the Bayesian compressive sampling (BCS) paradigm is proposed for the reconstruction of sparse distributions of weak scatterers. Towards this end, the original inverse scattering problem is recast to a probabilistic sparseness constrained optimization by introducing suitable hierarchical priors as sparsity constraints. A fast relevance vector machine (RVM) is then employed to reconstruct the scatterers as well as to estimate the “confidence level” of the inversion. Representative numerical results are presented to illustrate the method as well as to assess its potentialities and limitations in terms of inversion accuracy, computational efficiency, and robustness. Comparisons with state-of-the-art deterministic and stochastic reconstruction methodologies still within the Born approximation (BA) are discussed, as well.

Bayesian Compressive Sensing Approaches for the Reconstruction of Two-Dimensional Sparse Scatterers Under TE Illuminations

In this paper, the reconstruction of sparse scatterers under multiview transverse-electric illumination is dealt with. Starting from a probabilistic formulation of the “inverse source” problem, two Bayesian compressive sensing approaches are introduced. The former is a suitable extension of the single-task method presented earlier for the transverse-magnetic scalar case, while the other exploits an innovative multitask implementation to take into account the relationships among the “contrast currents” at the different probing views. Representative numerical results are discussed to assess, also comparatively, the numerical efficiency, the accuracy, and the robustness of the proposed approaches.

MT – BCS-Based Microwave Imaging Approach Through Minimum-Norm Current Expansion

An innovative three-step technique based on the multi-task Bayesian compressive sensing (MT - BCS) strategy is introduced to image 2D-sparse dielectric profiles. The proposed approach reformulates the contrast source mathematical description of the inversion problem into two fictitious real-valued ones jointly solved through a fast Relevance Vector Machine by taking into account the inter-relationships between the real and the imaginary parts of the unknown equivalent currents. Selected results from a numerical validation are presented and discussed to comparatively assess the accuracy, the robustness, and the computational efficiency of the proposed implementation.

Almost Time-Independent Performance in Time-Modulated Linear Arrays

This letter deals with the optimization of the switch-on instants of the radio-frequency (RF) switches used for the synthesis of time-modulated linear arrays (TMLAs). It is shown that these additional degrees of freedom allow one to increase the stability of the pattern instantaneously radiated by the antenna. Representative results, obtained by means of a particle swarm (PS) optimization, are reported and discussed.

Bayesian compressive optical imaging within the Rytov approximation

Within the range of validity of the Rytov approximation (RA), an innovative Bayesian compressive sensing (BCS) inverse scattering technique is developed. Potentialities and limitations of the BCS-RA method are validated through numerical experiments and representative results are discussed.

Synthesis of Time-Modulated Planar Arrays with Controlled Harmonic Radiations

This paper presents a technique for the control of the sideband radiations in time-modulated planar arrays. The proposed method is aimed at generating a desired pattern at the carrier frequency as well as reducing the power losses and interferences related to the harmonic radiations. By acting on both the durations and the commutation instants of the time pulses controlling the element switches, a method based on the Particle Swarm Optimizer is applied. Representative results are reported and discussed to show the effectiveness of the proposed approach.

Pulse-Shaping Strategy for Time Modulated Arrays—Analysis and Design

Time-modulated arrays (TMAs) are antenna systems where the transmitted or received signal is modulated by periodic time pulses. Several strategies have been proposed for defining the characteristics of the pulse sequence to control the antenna radiation pattern starting from the hypothesis of ideal radio-frequency (RF) switches with instantaneous rise and fall time. In this paper, the use of switches having a non-null transition between the on and off state is taken into account and the impact on the radiation features is studied and verified through a set of numerical results also in comparative fashion with ordinary rectangular pulses.

Maximum Efficiency Beam Synthesis of Radiating Planar Arrays for Wireless Power Transmission

The synthesis of radiating planar arrays for wireless power transmission (WPT) is discussed. The objective is the maximization of the ratio between the power radiated on a target area and the total transmitted power. The optimal tapering is analytically found as the solution of a generalized eigenvalue problem whose descriptive matrices are either computed in closed-form or obtained through numerical integration depending on the problem geometry. A set of representative numerical results concerned with different transmitting apertures and target areas is presented.