Full-Duplex Nonreciprocal Beam Steering by Time-Modulated Phase-Gradient Metasurfaces

We present the concept, theoretical model, and experimental implementation of a full-duplex nonreciprocal-beam-steering transmissive phase-gradient metasurface. Such a metasurface is realized by exploiting the unique properties of the frequency-phase transition in time-modulated twin unit cells. The metasurface may be placed on top of a source antenna to transform the radiation pattern of the source antenna, and introduce different radiation patterns for the transmit and receive states. In contrast to the recently proposed applications of time modulation, here the incident and transmitted waves share the same frequency. The metasurface is endowed with directive, diverse, and asymmetric transmission and reception radiation beams, and tunable beam shapes. Furthermore, these beams can be steered by simply changing the modulation phase. The proposed twin unit cells inherently suppress undesired time harmonics, leading to a high conversion efficiency, which is of paramount importance for practical applications such as point-to-point full-duplex communications.