Generation of multiple modes microwave vortex beams using tunable metasurface

In this paper, an active metasurface for vortex beam generation is proposed. This metasurface can transform the incident plane wave into vortex beams carrying orbital angular momentum (OAM) in four different modes. This active metasurface is composed of an array of varactor diodes loaded unit cells. The transmission phase of each metasurface unit cell can be fully controlled by the capacitance of the varactor diodes. Thus, it can generate four modes of vortex beams separately by simply changing the transmission phase distribution on the metasurface aperture. The properties of the proposed active metasurface is demonstrated by simulation results and have a good agreement with the theoretical design.