Planar antennas with advanced radiation features will play a prominent role in a number of key areas, ranging from future (5G) wireless communication networks to imaging systems for security screening and biomedical applications, radar and environmental remote sensing, and wireless power transfer.
The proposed research aims at the analysis, design and experimental characterization of novel planar radiators operating at microwave and millimeter-wave frequencies and based on the exploitation of higher or broken spatial symmetries. Electromagnetic systems based on periodic structures with such kinds of symmetries (or lack thereof) have been explored during the last few years, revealing intriguing and very promising propagation and radiation features. In this proposal the focus will be on traveling-wave antennas based on the excitation of leaky waves; in particular, three aspects will be addressed: i) modal propagation in 1-D periodic 2-D structures with broken symmetry in the unit cell; ii) radiation from cylindrical leaky waves with higher azimuthal order in uniform or radially periodic structures; iii) planar structures with transverse dilation symmetry.
General multilayered structures will be considered, comprising both homogeneous dielectric media, metal ground planes, and thin metallized layers, amenable to a simple and cost-effective realization and deployment. The designs will be crucially based on accurate modal analyses, with particular reference to complex (leaky) modes, i.e., to partially radiative regimes. Full-wave numerical simulations will also be performed, to validate the theory and the effectiveness of the developed solutions. Prototypes of selected designs will also be realized and experimentally characterized.
In this project, we propose three different kinds of innovative leaky-wave antenna (LWA) designs which possess advanced radiating features, particularly suitable for the next-generation 5-G communication paradigm. As a matter of fact, current antenna technologies for wireless communcations are typically based either on wire, or patch resonant elements. As a result, the radiation performances of these antennas are rather limited in terms of gain and bandwidth capabilities. In addition, it is not possible to arbitrarily reshape the pattern of such antennas, unless to employ them in array configurations and consequently increase the costs and the complexity of the design. In this regard, LWAs offer a good compromise to meet the requirements of a cost-effective planar design with a simple feeding mechanism, offering several degrees of freedom to reshape the radiation pattern without resorting to array configurations. However, conventional LWA designs generally exhibit poor radiation features when scanning through broadside (open stop-band condition), and this issue mainly motivated their scarce employment in wireless communications. Although several solutions have been proposed so far to circumvent this issue, a simple and effective means to completely suppress the open stop-band is still lacking.
To this aim, we first propose here a 1-D periodic 2-D LWA as a novel LWA design which is capable of completely suppress the open stop-band and thus efficiently radiate at broadside, thanks to the use of an asymmetric unit-cell. In the frame of this project, we will show under a rigorous theoretical framework that breaking the symmetry inside the unit-cell provides for a simple technique to suppress the open stop-band, as well as an additional degree of freedom to optimize the antenna performance.
With the aim of enriching the antenna platforms for 5-G communications of new advanced features, we will then investigate the potentialities offered by LWAs capable of radiating higher-order cylindrical leaky waves in the near-field. Indeed, such waves can carry OAM of different orders (OAM states of different order are mutually orthogonal), thus they can provide for an alternative means to realize a multiple-input multiple-output (MIMO) system in the near-field region, as opposed to conventional MIMO systems that typically operate in the far-field and are realized through array systems.
Finally, the radiation features of pseudo-periodic LWA structures whose unit elements possess dilation symmetry over the radiating aperture plane will be investigated under the frame of an original, still rigorous theoretical framework. As Floquet-Bloch modes for periodic structures, a complete orthogonal set of modes is expected to exist for structures obeying to homothetic transformations. The aim of this part of the project is to find such basis, understand its properties, and use them to tailor radiation with additional degrees of freedom.
Advancement potential:
The three antenna types proposed here all represent a significant advancement with respect to the state of the art. Specifically, the 1-D periodic 2-D LWA with an asymmetric unit-cell has been proposed only recently, without providing any connection between the break of the symmetry and the open stop-band suppression. As a consequence, it still lacks a rationale to design such structures and part of this project aims to provide for them. On the other hand, the properties of cylindrical leaky waves have been derived in the 90s only for the zeroth and the first order, in the far-field. Here, we aim at extending the theory of cylindrical leaky waves to arbitrary integer orders, and even fractional ones, in both the near-field and the far-field. Morevover, no experimental realizations exist of LWAs producing higher-order cylindrical leaky waves. Furthermore, the electromagnetic properties of unit-cell under homothetic transformation have not been investigated yet, thus their application to the realization of a LWA should be considered a completely new topic, accurately investigated for the first time in this research project.