Combinatorial Phase Modulation of Dual-Metasurface Plates for Designing Low Sidelobe Transmitarray Antennas With High Aperture Efficiency

A novel method is proposed for designing a low sidelobe level (SLL) transmitarray antenna (TA) with high aperture efficiency (AE). In this method, two phase-only metasurface plates are cascaded and coordinated to achieve amplitude modulation and phase alignment. The first phase-only metasurface plate is employed to realize the Chebyshev amplitude distribution of low sidelobes over the aperture of the second phase-only metasurface plate, where the aperture field phase can be subsequently aligned. The phase-only metasurface-based aperture amplitude modulation can effectively avoid energy loss, and it can simultaneously enhance the spillover efficiency to compensate for taper efficiency loss resulting from sidelobe suppression, thereby achieving low sidelobes while avoiding the loss of AE. Besides, to facilitate the specific design of Chebyshev distribution through phase modulation, a fast and efficient method is developed. Finally, to demonstrate the effectiveness of the proposed method, two TAs (termed TA1 and TA2, respectively) are designed, fabricated, measured, and compared. TA1 is a TA with optimal AE, and TA2 is designed based on the proposed method of low sidelobes without the loss of AE. Finally, TA2 achieves SLL of −27.2 dB (7.8 dB lower than TA1), a gain of 25.48 dB, and AE of 49.18% (0.26 dB and 3% lower than TA1, respectively). The proposed design method overcomes the loss of AE during sidelobe suppression, which presents new guidance for designing a low sidelobe TA with high AE.