In this article, we review some of the recent efforts and advancements in the implementation of reconfigurable metasurfaces and metamaterials tailored for antenna applications. Originally limited by fixed properties, these structures are increasingly integrated with different technologies to achieve real-time reconfigurability and versatility in response to evolving operational conditions and constraints. This work investigates the motivations and technical approaches driving this development, with a specific focus on reconfigurable metasurfaces designed for antenna systems operating within the microwave range (L-band to K-band). By analyzing limitations and experimentally validated approaches, the article offers a comprehensive exploration of the performance and limitations of common reconfigurability schemes in microwave metadevices.

The design of metasurfaces and metasurface-based devices (e.g. reflective intelligent surfaces - RIS) is inherently affected by unpredictable variations of the unit-cell response, due, for instance, to fabrication tolerances, physical discontinuities, presence of bumps, etc. Such effects may dramatically affect the accuracy of the conventional design models, such as the one based on the local surface impedance (LSI). In this work, we present a statistical model resulting in a probability density function that allows defining a random local surface impedance (rLSI), that takes properly into account potential random variations derived from the von Mises distribution. To compensate for these variations, we propose a transformation kernel that matches the expected rLSI value to the design target. By using an analytical formulation and a proper set of full-wave simulations, we demonstrate the effectiveness and robustness of the method against unpredictable variations caused by the mutual coupling among the unit-cells and fabrication tolerances/errors. The proposed method paves the way to foster advancements in realistic metasurface engineering.

Temporal metamaterials have been recently exploited as a novel platform for conceiving several electromagnetic and optical devices based on the anomalous scattering response arising at a single or multiple sudden changes of the material properties. However, they are difficult to implement in realistic scenarios by switching the permittivity of a material in time, and new strategies to achieve time interfaces in a feasible manner must be identified. In this paper, we investigate the possibility to realize a temporal metamaterial without acting on the material properties, but rather on the effective refractive index and wave impedance perceived by the wave during the propagation in an empty guiding structure by varying the boundaries in time. We demonstrate analytically and through numerical experiments that suddenly changing the physical distance between the metallic plates of a parallel-plate waveguide will induce an effective temporal interface. In addition to the standard backward and forward scattered fields at different frequencies due to the temporal interface, we also identify the presence of a static field necessary to satisfy the continuity of the electromagnetic field across the interface. The proposed concept can be extended to temporally controlled metasurfaces, opening an easier path to the design and realization of novel devices based on time-varying metamaterials at microwave and optical frequencies.