Tunable Perfect Anomalous Reflection Using Passive Aperiodic Gratings

Realizing continuous sweeping of perfect anomalous reflection in a wide angular range has become a technical challenge. This challenge cannot be overcome by the conventional aperiodic reflectarrays and periodic metasurfaces or metagratings. In this paper, we investigate means to create scanning reflectarrays for the reflection of plane waves coming from any direction into any other direction without any parasitic scattering. The reflection angle can be continuously adjusted by proper tuning of reactive loads of each array element, while the geometrical period is kept constant. We conceptually study simple canonical two-dimensional arrays formed by impedance strips above a perfectly reflecting plane. This setup allows fully analytical solutions, which we exploit for understanding the physical nature of parasitic scattering and finding means to overcome fundamental limitations of conventional reflectarray antennas. We propose to use subwavelength-spaced arrays and optimize current distribution in $\lambda/2$-sized supercells. As a result, we demonstrate perfect tunable reflection to any angle. Our work provides an effective approach to design reconfigurable intelligent surfaces with electrically tunable reflection angles.