One of the main challenges of beyond-5G wireless communications is the realization of energy-efficient high data-rate links. In this regard, wireless near-field links have been proposed as an alternative to most conventional wireless far-field links. Indeed, in the near-field region it is possible to generate electromagnetic waves with limited diffractive spreading, also known as localized waves, for which the link budget no longer obeys the Friis equation. However, radiating systems capable of generating localized waves in the mm-wave and terahertz (THz) range are lacking, and those available suffer from high costs and/or design complexity.
In this project, we propose to analyze, design, and experimentally validate mm-wave/THz radiating systems not only capable of generating localized waves, but also equipped of novel features with respect to the state of the art. Specifically, we aim to realize advanced radiating systems with both improved focusing efficiency and tunable properties. In both cases, the reference structures are leaky-wave antennas (LWAs), as they offer a low-cost, low-profile solution to realize planar radiating devices capable of generating localized waves. Among the various types of localized waves, we will focus on the generation of Bessel-like beams, as they retain exceptional focusing and power transport properties compared to other localized solutions.
In order to improve the focusing efficiency of current mm-wave and THz systems, here we wish to investigate the possibility of generating Bessel-Gauss beams through LWAs. Similar structures will be equipped of tunable elements to offer the possibility to reconfigure the beam shape by the application of an external driving voltage: in the millimeter-wave range, we will consider p-i-n diodes as tunable elements, whereas in the THz range, we will consider graphene sheets and/or liquid crystals. Full-wave numerical simulations and experimental campaigns are planned to validate the proposed theory.
The proposed project has various elements of novelty in the wide context of next-generation wireless communications wireless power transfer, and near-field imaging systems. The most significant are outlined below.
First, most of wireless paradigms for beyond-5G communications are based on wireless far-field links, while only a few have proposed wireless near-field links. However, current solutions are based on expensive, non-planar, complex designs; all aspects that hinder their distribution on a large scale. Conversely, leaky-wave antennas (LWAs) as those proposed here are cost-effective, low-profile, planar, and easy to fabricate. The realization of a wireless near-field link through a leaky-wave antenna would definitely represents a significant breakthrough in this context.
Second, LWAs capable of generating localized waves have only been preliminarly proposed by our research group, mainly in the microwave range. Moreover, the existing devices are capable of generating a specific kind of localized-wave solution, viz., the Bessel beam, not considering the possibility to either improve the beam features. In particular, the generation of Bessel-Gauss beams at microwave frequencies has not been discussed in the open literature. As a matter of fact, Bessel-Gauss beams have widely been investigated in the optical range, where a convenient scalar, ray-optics approximation allows for a simplified theoretical treatment of these solutions. Conversely, in the microwave range, a full-wave approach is needed. Consequently, the analysis, design, fabrication, and experimental validation of a planar device capable of generating Bessel-Gauss beams at mm-waves would represent an important advance from both a physical and an engineering viewpoint.
Third, tunable antennas are commonly designed to offer pattern reconfigurability in the far-field region. As is known, tunable antennas have been proposed in the last decades as an alternative to more complex and expensive active electronically-scanning arrays (AESAs). In this context, the term 'reconfigurability' is often referred to the capability for an antenna to change certain far-field radiating properties, such as the pointing angle, pattern shape, the beamwidth while maintaining the others fixed. Conversely, an analogous definition of reconfigurability does not apply in the near-field region where the classical definition of radiation pattern does not hold. Nevertheless, the possibility to reconfigure the beam features in the near-field region is of paramount importance for wireless applications; the dynamic control of the beam waist and the extent of the covering distance may pave the way for energy-efficient wireless near-field links. This project aims at filling this technological gap.
Fourth, graphene is an exceptional material with unique properties, especially in the THz range where it has been recently proposed for the realization of planar, low-profile antennas. The main application of graphene in THz radiating devices is for obtaining the steering of the beam at a fixed frequency by changing the voltage applied between the graphene sheet and a gating pad placed underneath. Recently, this principle has been applied to Fabry-Perot leaky-wave antennas (FPC-LWAs) on a theoretical basis. However, to the Authors' best knowledge the tunable properties of graphene have not been applied for realizing reconfigurable devices operating in the near-field region.
As emphasized in the previous items, the possibility either to improve the focusing efficiency of wireless near-field links or to dynamically reconfigure the beam features of the radiated waves is an area that is still rather unexplored and potentially capable of introducing a technological breakthrough for the forthcoming beyond-5G wireless communications. Realizing such devices by resorting to leaky-wave antenna technologies is not only an additional element of novelty, but it is also an exceptional market opportunity, thanks to the simplicity and cost effectiveness of these solutions.