  A novel polarized reflectarray is designed, fabricated, and experimentally
characterized to show its flexibility and efficiency to control wave generation
and focusing of orbital angular momentum (OAM) vortices with desirable OAM
modes in the microwave frequency regime. In order to rigorously study the
generation and focusing of OAM, a versatile analytical theory is proposed to
theoretically study the compensation phase of reflectarray. Two prototypes of
microwave reflectarrays are fabricated and experimentally characterized at 12
GHz, one for generation and one for focusing of OAM-carrying beams. Compared
with the OAM-generating reflectarray, the reflectarray for focusing OAM vortex
can significantly reduce the beam diameter, and this can further improve the
transmission efficiency of the OAM vortex beams. We also show that the
numerical and experimental results agree very well. The proposed design method
and reflectarrays may spur the development of new efficient approaches to
generate and focus OAM vortex waves for applications to microwave wireless
communications.
