Phase-Gradient Metasurfaces for Efficient Conversion of Surface Wave to Propagating Wave

Transmission of light through subwavelength apertures surrounded by periodic structures have attracted extensive research interests since the last two decades. In this work, we propose a method to achieve directional transmission of electromagnetic waves diffracted by a subwavelength aperture using phase-gradient metasurfaces instead of grating structures. Near-field distributions from both numerical simulations and experimental measurements are presented to validate the concept. The extraordinary transmission is further maintained over a non-negligible frequency band ranging from 9 GHz to 12 GHz by modulating the phase profile of the metasurface through electronically-controlled varactor diodes inserted in the constituting unit cells of the metasurfaces.