Design of Orbital Angular Momentum Antennas With Low Sidelobes

This letter develops a novel synthesis method for the circular aperture orbital angular momentum (OAM) antennas. The method, derived from the continuous aperture, effectively reduces the sidelobe levels (SLLs) of OAM waves and can achieve precise adjustments. Moreover, a discretization method is proposed, thus extending the applicability of the synthesis method to discrete arrays. Compared to the traditional direct sampling method, the proposed method can reduce the performance degradation of antennas in terms of SLL caused by discretizing continuous aperture distributions, especially for high-order OAM waves. Using the proposed approaches, a complex amplitude transmission metasurface is designed to generate a second-order OAM wave with the desired SLLs of -25 dB. Experimental results show that the SLLs of the E-plane and H-plane are -22.87 and -23.02 dB, respectively. The effectiveness of the approaches for controlling SLL is demonstrated by theoretical analyses, simulations, and experiments.