Ricerc@Sapienza

A planar antenna radiating twisted beams with different azimuthal order and a consistent beam angle is designed by employing a single uniform circular array embedded in a Fabry–Perot cavity. Circular phased arrays placed in free space are commonly employed to radiate conical beams carrying orbital angular momentum. However, the beam angle depends on both the array radius and the azimuthal order of the beam, thus requiring the use of multiple concentric circular arrays in order to produce beams with different azimuthal order and a common beam angle.

The gradual transition from a reactive to a radiative regime is studied for leaky modes supported by multilayered planar open waveguides.

In this work, we propose an azimuthally-invariant periodic leaky-wave radiator for the generation of Bessel beams and X-waves by means of backward cylindrical leaky waves at millimeter wavelengths. A rigorous framework is first outlined to understand the theoretical constraints of such novel design. A specific attention is devoted to the impact of the attenuation constant on the focusing properties of the device. On this basis, a practical design is then proposed to meet the previous requirements.

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.

A novel terahertz (THz) Fabry–Perot cavity (FPC) antenna is proposed, based on a multistack of alternating layers of highly birefringent nematic liquid crystal (NLC) and highpermittivity dielectric, which comprehensively acts as a Bragg reflector. This layout is able to provide enhanced reconfigurability

We analyze and experimentally demonstrate the possibility of generating X-waves at microwave and millimeter-wave frequencies by means of a partially open radial parallel-plate waveguide antenna. The structure is azimuthally symmetric and fed in the center by means of a simple vertical coaxial probe, which excites a cylindrical leaky wave. Radially periodic annular slots etched in the upper metal plate allow the propagation of a backward leaky wave, as required for generating Bessel beams in the near-field region.

In this work, we propose an azimuthally-invariant periodic leaky-wave (LW) radiator for the generation of Bessel beams and X-waves by means of backward cylindrical LWs at millimeter wavelengths. A rigorous framework is first outlined to understand the theoretical constraints of such a novel design. A specific attention is devoted to the impact of the attenuation constant on the focusing properties of the generated Bessel beams. On this basis, a practical design is then proposed to meet the previous requirements.

In this contribution, we describe the design and the radiation features of a dual-mode operation low-profile, low-cost, wideband antenna. The structure is made by an annular, 2-D radially periodic, leaky-wave antenna enabling the generation of both high-gain beams in the far-field and of nondiffracting waves within the near-field radiative region. This is obtained through the generation of a fast backward spatial harmonic supported by a metal-strip grating placed on a grounded dielectric slab.

The generation of higher-order cylindrical leaky waves (HOCLWs) by means of canonical electric or magnetic ring sources was discussed in Part I, where radiation formulas for such waves were also presented. In the second part of this sequence, the practical excitation of HOCLWs in a Fabry–Perot cavity antenna is discussed considering the use of ring sources in a discrete form, i.e., circular phased arrays of vertical electric or horizontal magnetic dipoles.

Radiation from cylindrical leaky waves (CLWs) supported by layered dielectric media is of interest in a variety of current applications. A comprehensive two-part study has been undertaken to investigate the generation and the radiation properties of CLWs with an arbitrary integer azimuthal order n. The first of this two-part sequence deals with the identification of continuous rings of canonical sources of electric and magnetic types, capable of exciting higher-order CLWs (HOCLWs) in planar open radial waveguides.