Multibeam Generation Using a High-Efficiency Dual-Band Quad-Polarized Transmit-Reflectarray

This letter presents a dual-band quad-polarized (DBQP) transmit-reflectarray (TRA) with an array aperture only 0.11λ_L in thickness for bidirectional multi-beam coverage across both half-spaces. The unit cell generates independent phase responses for Ka-band left-/right-hand circularly polarized (LCP/RCP) transmission and reflection, and for K-band x-/ylinearly polarized (XLP/YLP) transmission and reflection, enabling an independent bidirectional four-channel TRA. An odd-even element phase difference method is introduced to generate co-frequency co-polarization multi-beams, achieving equal-gain dual beams, and a novel analytical phase compensation approach is further proposed to equalize broadside and off-axis tri-beams. A DBQP ten-beam array is thereby synthesized, generating three LCP transmitted and two RCP reflected beams in the Ka-band, alongside two XLP transmitted and three YLP reflected beams in the K-band. Measurements demonstrate axial ratios <3 dB (25.30 GHz), cross-polarization levels <−20 dB (18.22 GHz), and peak aperture efficiencies >40% in both bands, making this architecture a promising candidate for quasi-stationary nodes in future space–air–ground–sea integrated networks (SAGSIN).