Wideband Sub-Wavelength Orbital Angular Momentum Reflectarray Antenna

A circular aperture wideband reflectarray antenna (RA) with orbital angular momentum (OAM) pattern is analyzed and designed. The proposed subwavelength element includes two circular, co-centered rings with variable diameter. While the outmost diameter remains constant, the radii of inner and outer inner ring gradually advance in the opposite directions. This design process in the proposed multi-resonance element reduces the slope of the phase-length curve and element loss. As a result, the efficiency and bandwidth of the antenna increase. Two structures with linear polarization OAM RA have been designed which the first one is a center-fed center-beam with mode (l) +1 and the second is an offset-fed offset-beam with l=+2. Results indicate the maximum gain of 21.4dBi at 10.5 GHz with 31% 1dB gain bandwidth for l=+1 OAM RA and peak gain of 18.9 dBi at 10.4 GHz with 30% 1dB gain bandwidth for l=+2 OAM RA.