Parabolic Reflector for UCA-based OAM Multiplexing in Sub-THz Band and Transmission Experiment

This paper proposes a reflector antenna to enlarge the aperture of a uniform circular array (UCA) for long-range orbital angular momentum (OAM) multiplexing with the Butler matrix in sub-terahertz (sub-THz) band, and it reports the antenna design and experimental evaluation of wideband data transmission with OAM multiplexing. We devise a parabolic reflector antenna consisting of two reflectors (a main reflector and a sub reflector) sharing a focal point and have different focal lengths, which allows the antenna aperture to be enlarged while maintaining the distribution of radiated waves from a fed antenna with a two-dimensional distribution such as UCA. We design and fabricate the reflector antenna to enlarge the aperture of a 6 cm diameter UCA to 30 cm with a focal length ratio of 5. The antennas are incorporated into a transmitter and receiver of an OAM multiple transmission system consisting of a Butler matrix, and transmission experiments are conducted. The experimental results confirm that the orthogonality of the OAM modes is maintained, and wireless multiplex transmission of 707.73 Gbit/s at a distance of 20 m is achieved using 8 OAM modes in a 32 GHz bandwidth.