Design of an Optically Transparent OAM Digital Coding Metasurface With Low RCS

In this letter, an asymmetrically transmissive, optically transparent and multi-bit digital coding metasurface with low radar cross section (RCS) has been proposed based on the Pancharatnam -Berry (PB) principle and transmission phase theory. The metasurface provides high transmittance and a phase gradient from 17.0 to 20.5 GHz. Its 3-bit unit cells are divided into four groups and realize cross-polarization transmittance over 0.7 with phase difference of 90° between groups. In the band of 22.0-27.0 GHz, the unit cells are reorganized into two groups, which reflectance of co-polarization above 0.95 and the phase difference is 180° between them. Through a specific coding sequence based on these principles, the metasurface with the transmittance of 48.42% can transmit x-polarized waves into vortex beams with orbital angular momentum (OAM) in 17.0-20.5 GHz and reduce RCS of oppositely y-polarized incidences in 22.0-27.0 GHz. The metasurface holds significant application in transparent scenarios such as glass curtain walls, aircraft canopies, and windows in space station.