A Polarization-Reconfigurable Orbital Angular Momentum Active Folded Transmitarray Antenna

A polarization-reconfigurable, low-profile active folded transmitarray antenna capable of orbital angular mo-mentum (OAM) generation is presented. The proposed antenna consists of an upper active transmissive metasurface (UATM), a lower polarization-conversion reflective metasurface (LPCRM), and an magnetoelectric dipole feed. The UATM is composed of five metallic conductive layers and three dielectric layers, featuring identical top and bottom metallic layers, each inte-grating two positive-intrinsic-negative (PIN) diodes aligned along the x-axis and two PIN diodes along the y-axis. Full-wave simulation results demonstrate the generation of a polarization-reconfigurable OAM beam with mode <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$l=+1$</tex>, achieving mode purity of 70% for x-polarization and 72% for y-polarization. Moreover, the overall antenna height is reduced to one-third of the focal length.