Ricerc@Sapienza

Recent studies highlighted deep-penetration properties of inhomogeneous waves at the interface between a lossless and a lossy medium. Such waves can be generated by means of radiating structures known as Leaky-Wave Antennas (LWAs). Here, a different approach is proposed based on the use of a lossy prism capable to generate an inhomogeneous wave when illuminated by a homogeneous wave. The lossy prism is conceived and designed thinking of Ground-Penetrating Radar (GPR).

In this work, the tunable properties of nematic liquid crystals are exploited in order to design a Fabry-Perot cavity (FPC) leaky-wave antenna (LWA) with beam steering capability at fixed frequency in the THz range. The considered design is a grounded dielectric slab covered with a multistack of alternating layers of low- and high- permittivity dielectric materials, consisting of nematic liquid crystals and alumina thin films, respectively. The former allows for achieving the beam-steering capability at a fixed frequency.

Tunable THz antennas based on a single unpatterned graphene sheet placed inside a grounded dielectric multilayer are studied with the aim of characterizing their performance in terms of pattern reconfigurability, directivity, and radiation efficiency. The considered structures belong to the class of Fabry-Perot cavity (FPC) antennas, whose radiation mechanism relies on the excitation of cylindrical leaky waves with an ordinary (i.e., non-plasmonic) sinusoidal transverse modal profile.

We propose a simple phased-array design based on a Fabry-Perot cavity antenna for the generation of a highly-directive pencil beam steerable along two directions in 3-D space. Each array element generates an element pattern in the far-field obtained through the excitation of a dominant cylindrical TM leaky wave inside the cavity. Hence, the resulting conical pattern is combined with the array factor of a N × N square or circular arrangement of ideal vertical electric dipoles.

We present the design and analysis of a K-band radially-periodic leaky-wave antenna radiating a circularly polarized broadside pencil beam. The structure is constituted by a metallic strip grating printed on top of a single-layer grounded dielectric slab, and is fed on the bottom by means of a square array of printed surface-wave launchers. The structure is optimized to support the fast n = -1 spatial harmonic, whose behavior has been accurately characterized through a full-wave dispersive analysis developed by means of an in-house method-of-moments (MoM) code.

An annular periodic leaky-wave antenna (LWA) fed by a simple azimuth-symmetric source is designed to generate a high-gain omnidirectional conical beam pattern which scans with frequency over a wide angular range. The proposed structure is defined by a finite metallic radial strip grating printed on a grounded dielectric slab which supports an n = 0 cylindrical leaky wave (CLW) mode. The distinctive features of CLWs supported by such a truncated structure are also highlighted and discussed.

A two-dimensional leaky-wave antenna fed by an array of fully integrated sources and able to provide fixed-frequency continuous beam steering through broadside is presented in this contribution. The structure is constituted by a 'bull-eye' leaky-wave antenna fed by a proper arrangement of four surface-wave launchers, whose excitation coefficients are selected to control the beam pointing angle around broadside.

Periodic leaky-wave antennas are typically affected by the open-stopband (OSB) problem, i.e., the pattern degradation as the beam scans through broadside. Over the years, various techniques have been proposed to mitigate, or even suppress, this longstanding issue. However, most of these techniques cannot be easily applied to 1-D periodic 2-D structure. Recently, it has been theoretically and experimentally shown that the OSB can be suppressed by means of a very simple technique: it consists of designing a unit cell with two unequal discontinuities suitably spaced one another.

It has recently been shown that the relaxation time of a graphene sheet is the crucial parameter that governs the radiation performance in graphene THz antennas based on either plasmonic or nonplasmonic leaky waves. Moreover, the radiating properties of these devices have always been derived assuming an ideal dipole-like source, and no full-wave and experimental results on realistic feeders have been reported, yet. To this purpose, in this work we aim at bringing the designs of graphene-based Fabry-Perot cavity leaky-wave antennas (FPC-LWAs) towards an experimental stage.

The dispersive properties of the first higher order (EH1) mode in uniform graphene nanoribbons over a ground plane are numerically studied to point out the characteristics of the bound-mode and leaky-mode regimes. The graphene nanoribbon is then suitably designed to operate on the EH1mode as a frequency-scannable leaky-wave antenna in both the millimeter and terahertz ranges.