Future scenarios of wireless communication systems, in particular the envisioned 5G mobile network, call for technological advances enabling higher data rates, higher densities of users, device-to-device communications, as well as wireless power transfer.
In this framework, the proposed research aims at the analysis and design of novel planar radiators operating at microwave, millimeter-wave, and terahertz frequencies and based on the excitation of cylindrical leaky waves (i.e., of two-dimensional leaky-wave antennas, 2D LWAs), characterized by radiative features beyond the state of the art for this class of antennas. In particular, the focus will be on the synthesis of i) wideband directive broadside beams; ii) fixed-frequency, angle-reconfigurable conical beams; iii) focused radiation with non-zero orbital angular momentum (OAM) via backward leaky waves with higher azimuthal order.
Azimuthally symmetric 2D LWAs will be considered, based on a partially reflecting surface (PRS) constituted by an array of concentric ring slots placed on top of a suitable dielectric multilayer. The key design elements for achieving the desired radiative properties will be: the geometry of the radially-modulated PRS, possibly realized with graphene to achieve reconfigurability via electrostatic bias; the number and type of layers in the multilayer background structure; the unconventional lateral truncation of the antenna; the development of novel feeding structures aimed at imparting the desired azimuthal standing- or traveling-wave character to the relevant leaky waves.
The designs will be crucially based on accurate modal characterizations of the waves traveling radially along the considered antennas and will be validated through full-wave numerical simulations as well as through the realization of antenna prototypes and their experimental characterization.
This project proposes different innovative design strategies for microwave and millimeter-wave radiators aimed at operating in future (5G) WCSs.
State-of-art antenna solutions for wireless communications are based on printed or wire antennas of the resonant type, either in single (mobile unit) or array (fixed unit) configurations. To the best of our knowledge, traveling-wave solutions, with particular reference to LWAs, have not been considered so far for WCSs; their application is traditionally restricted to radar systems. LWAs have various attractive features, mainly: the simplicity of the feeding structure; the possibility to control the aperture field and hence add several degrees of freedom for shaping the radiation pattern with a straightforward design procedure based on modal analyses; the cost-effectiveness. In this project, circularly-symmetric 2D LWAs are proposed for achieving different design goals relevant to communication scenarios and referred to both far-field patterns and near-field properties, while remaining within the typical technological constraints of microwave/millimeter-wave fabrication processes.
First, the typical narrowband character of LWAs with a fixed (i.e., not scannable) beam angle is challenged by a suitable dispersion engineering of a radially periodic structure and its unconventional truncation, in order to obtain wideband broadside radiation in the form of omnidirectional directive pencil beams.
Second, whereas the beam angle of LWAs is typically scanned by varying the operating frequency, the possibility to reconfigure the antenna pattern is explored here at a fixed frequency considering graphene-based radiators in the THz regime. In particular, reconfigurability will be achieved via selective electrostatic bias of the circular graphene rings, which constitute the upper plate of the antenna, with the goal of varying the pattern shape from a pencil broadside beam to a conical scanned beam with variable aperture angle.
Third, the exploitation of OAM as an additional degree of freedom for enhancing the capacity of the communication channel will be explored for the first time in connection with the excitation on 2D LWAs of cylindrical LWs having higher azimuthal order. The study of such waves is still lacking in the current literature. The simplicity of the relevant feed, if constrasted with typical current OAM radiators based on circular phased arrays, prompts a theoretical analysis of OAM transport properties of cylindrical LWs in the near field as well as an investigation of practical structures capable of generating them.
Advancement potential:
The possibility of employing 2D LWAs as radiating systems in wireless scenarios is an area that is both still unexplored and potentially capable of introducing a technological breakthrough as needed by the envisioned requirements of 5G wireless mobile networks. The main drivers of the present investigation are constituted by the promising features of 2D LWAs in terms of simplicity and hence cost effectiveness, with particular reference to fixed radiating units to be employed in outdoor as well as indoor networks.