Dynamic Manipulation of Multimode Electromagnetic Vortex Beam by 2-bit Programmable Transmissive Metasurface

Here, we propose a design method for a 2-bit transmissive programmable metasurface and demonstrate the generation and dynamic control of multimode electromagnetic vortex beams. By adjusting the states of the loaded PIN diodes, the metasurface element achieves high-efficiency transmission with an insertion loss as low as 1.2 dB and precise 2-bit tunable phase control at a center frequency of 4.15 GHz. The coding schemes necessary for generating steerable vortex beams are then theoretically derived. To validate the design principle and simulation results, a metasurface prototype is fabricated. Near-field scanning measurements show that the proposed metasurface can dynamically generate vortex beams with various modes, exhibiting distinct spiral phase characteristics and annular amplitude distributions, with the mode purity of the dominant mode remaining above 0.88 for orders within ±2 at the center frequency. Far-field radiation pattern measurements further confirm that the generated vortex beams can be dynamically scanned within 0°～45°, with a scan loss of less than 3 dB. The results measured align well with the simulations. The proposed programmable metasurface for vortex beam control demonstrates strong potential for applications in radar imaging and wireless communication.