Spin-Decoupled Anisotropic Metasurfaces With Chirality-Assisted Amplitude Modulation for a Low-Sidelobe Dual-Circularly Polarized Transmitarray

In this article, we propose an amplitude-modulated spin-decoupled anisotropic metasurface and its application to a dual-circularly polarized (dual-CP) transmitarray (TA) with suppressed sidelobe levels (SLLs). It is achieved by merging the propagation phase, Pancharatnam-Berry (PB) phase, and chirality in a meta-atom. A developed homogenized model is first analyzed to guide the design of broadband vialess transmissive meta-atom realizing a propagation phase coverage of $2\pi $ . Then, a dual-rotation strategy, that is, exterior and interior rotations, is utilized to introduce the PB phase and chirality-assisted amplitude modulation, respectively. Hence, independent beamforming for left- and right-handed CP waves is achieved with tailorable amplitude. As proof-of-concept examples, two dual-CP TAs, without and with amplitude control, are synthesized, fabricated, and measured, demonstrating that the SLL of the designed TA can be reduced by around 6 dB when involving amplitude control. The measured results showcase suppressed SLLs around −27 dB, an aperture efficiency of 31.3% and 28.6% for left- and right-handed CP beams, as well as a 3-dB gain and axial ratio (AR) bandwidth of 22.3% and 23.2%, respectively. The design methodology and the proposed low-SLL dual-CP TA are promising in communication systems for space and wireless applications.