Dynamic millimeter-wave OAM beam generation through programmable metasurface.

Millimeter-wave (mmWave) and orbital angular momentum (OAM) multiplexing are two key technologies for modern wireless communications, where significant efforts have been devoted to combining these two technologies for extremely high channel capacities. Recently, programmable metasurfaces have been extensively studied for stimulating dynamic multi-mode OAM beams, owing to their ability of subtle dynamic modulation over electromagnetic waves in a digital manner. However, programmable metasurfaces for mmWave OAM stimulation are rarely mentioned, due to the requirement of extremely high processing precision for mmWave applications. In this paper, a programmable metasurface is presented to stimulate dynamic multi-mode mmWave vortex beams. The proposed metasurface is composed of electronically reconfigurable units, which is obtained through configuration integration of a PIN diode within each radiation patch for modulating the unit resonant property. Both low reflection losses and stabilized inverse phase states are obtained for the binary unit coding states within the operation band. Through modulating the real-time coding distribution on the metasurface by programmable bias circuit, the generation of mmWave OAM beams with mode numbers  = 0,  = +1,  = +2, and  = +3 are numerically designed and experimentally verified. Our study paves a new perspective for the cross amalgamation of both mmWave and multi-mode OAM technologies.