Janus metagrating for tailoring direction-dependent wavefronts.

Janus metasurfaces have emerged as a promising platform to enable independent wave manipulation by fully exploiting the inherent propagation direction of electromagnetic waves. These structures allow achieving distinct wavefront functionalities based on the direction of wave propagation. Concurrently, metagratings have gathered significant attention as an innovative design scheme for wavefront manipulation, particularly in addressing the low efficiency issue commonly associated with conventional metasurfaces. This study introduces Janus metagratings as a means for tailoring efficient, direction-dependent absorption and reflection. Utilizing established analytical models, a precise analysis of diffraction modes is conducted in transmissive metagratings, facilitating asymmetric wavefront manipulation under the two incidence directions. By arranging distinct meta-atoms with specific load impedances on the upper and lower layers of the metagrating, efficient asymmetric wave responses are achieved. The design methodology is validated through full-wave simulations, which demonstrate strong consistency with theoretical predictions. Additionally, a Janus metagrating prototype is fabricated and tested in the microwave frequency regime, validating the direction-dependent wavefronts tailoring characteristics. The proposed design methodology offers a versatile platform for asymmetric propagation and advanced systems in future wireless and optical communication applications.