Ricerc@Sapienza

The possibility to generate a nondiffracting Bessel beam by means of a fast backward spatial harmonic supported by an annular metal-strip grating placed on a grounded dielectric slab is demonstrated. The focusing capabilities of the relevant leaky-wave aperture field are investigated in conjunction with the dispersive analysis of the considered structure. Full-wave simulations of a prototype are developed using a commercial code. The proposed design represents an attractive simple and low-cost solution potentially able to generate an arbitrary-order nondiffracting beam.

Bessel-beam launchers are promising and established technologies for focusing applications at microwaves. Their use in time-domain leads to the definition of a new class of devices, viz., the X-wave launchers, that are currently under theoretical investigation. In this work, we discuss the focusing features of such devices with a specific interest at millimeter waves. By reviewing the mathematical expressions that describe the spatial resolutions of these systems, we establish here novel operating conditions which might be particularly appealing for specific millimeter-wave applications.

A radially periodic two-dimensional leaky-wave antenna is studied for the generation of zeroth-order Bessel beams within a limited spatial region and over a wide frequency range. The antenna design is wideband and based on an annular metal strip grating placed on top of a grounded dielectric slab, supporting a cylindrical leaky wave with a fast backward spatial harmonic.

Bessel-beam launchers are promising and established technologies for focusing applications at microwaves. Their use in time-domain leads to the definition of a new class of devices, namely, the X-wave launchers. In this work, we discuss the focusing features of such devices with a specific interest at millimeter waves. The spatial resolutions of such systems are described under a rigorous mathematical framework to derive novel operating conditions for designing X-wave launchers. These criteria might be particularly appealing for specific millimeter-wave applications.

Bessel-Gauss beams have mainly been proposed in optics as a solution for reducing the on-axis intensity oscillations typical of Bessel beams. Previous investigations on Bessel-Gauss beams are based on a scalar theory in the paraxial approximation, and thus cannot be extended to the microwave range where a fully vectorial approach is needed. Here, the generation of Bessel-Gauss beams through leaky waves is investigated. First, the nondiffractive and focusing properties of Bessel-Gauss beams generated through leaky waves are extensively examined in the frame of a vectorial approach.

The attainable performances of a general formulation employing radiation matrix eigenfields of multi-port antennas to synthesize near-field distributions are investigated. Field synthesis performed on open or closed surfaces, proximate to or enclosing an antenna array, either based on both electric and magnetic target field distributions or just the former, are presented to illustrate key features of the synthesis technique and its sensitivity with respect to realistic random magnitude and phase variations of the array excitation profiles.

An energy-based representation suitable for the electromagnetic characterization of linear multiport circuits and antenna systems, as well as for the optimization of antenna beamforming and near-field radio frequency-focusing performances, is presented. Radiation, ohmic, dielectric power loss, and reactive power storage are described in the concise matrix form, yielding respective eigenmodes and eigenfields that rigorously account for all energetic processes.