Design of smart electromagnetic surfaces for next generation of communication systems

Smart electromagnetic surfaces (SESs) are novel technologies that have gained significant attention in the field of wireless communication. They are expected to play an important role in the development of 5G, 6G and future wireless communication systems, that will be asked to fast data transfer rates, wide bandwidth, better coverage and almost zero latency. These goals can be achieved using mm-waves or sub-THz frequency bands, that present several advantages. On the other hand, they also suffer from some limitations as higher free space loss, higher building penetration loss, and strong interaction with obstacles along the propagation path. To overcome these drawbacks without increasing the complexity and the cost of the systems, recently the possibility of exploiting the environment in which the signal propagates as a further degree of freedom has been investigated. The idea is to design a smart electromagnetic environment, that can actively contribute to improving the system performance. Its definition is possible thanks to the introduction of several active and passive devices that allow reaching blind spots or covering desired areas without increasing the number of base stations. Among them, there are SESs, i.e. thin surfaces designed to provide not specular reflection. Two possible solutions have been considered for their realization: in the first case, they are completely passive surfaces able to re-direct the incident field in a fixed direction, while an alternative consists in using reconfigurable surfaces that can change the direction of re-radiation by adjusting their behavior. Both the two solutions are realized subdividing the surface in unit cells that can have either a resonant or a sub-wavelength size. In both the cases, in its widely-used version, the unit cell consists in a metal patch, with a proper shape, printed on a thin dielectric layer located over a ground plane: varying one or more of the geometrical parameters of the patches it is possible to control its response, and in particular the reflection coefficient (or the surface impedance) it provides. In this context, the activity carried on during the thesis has been focused on the design of an innovative (passive) smart electromagnetic skin. The two main aspects on which the work concentrates are the following. Design of an innovative resonant unit cell with enhanced features. The result of this activity has been a new geometry able to provide a smooth variation of the phase of the reflection coefficient over a range of 360°, necessary to improve the SES bandwidth. Moreover, it possesses several free parameters, and therefore the possibility to varying simultaneously two of them has also been investigated. Design of a curved SES, to be integrated on a street light or a stop light pole. Such an innovative solution presents several advantages in comparison with the conventional one, in which the smart skin is mounted on the wall of a building. It has a lower visual impact and can be used also in areas as the historical centers of towns, it can be rotated on the pole to maximize the system’s performance, that is not affected by the not negligible contribution of the wall. The performance of both the unit cell and a curved SES designed with its use have been numerically tested and compared with solutions where the re-radiating element is a square patch or/and with planar SESs: the obtained results prove the effectiveness of the proposed configuration.