Multi-Beam 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 (transmission–reflection) multi-beam coverage across both half-spaces. The unit cell can generate independent phase responses for Ka-band left-hand circularly polarized (LCP) transmission and right-hand circularly polarized (RCP) reflection, as well as K-band x-linearly polarized (XLP) transmission and y-linearly polarized (YLP) reflection, enabling an independent bidirectional four-channel TRA. In the array design, an odd-even element phase difference method is introduced to generate co-frequency co-polarization multi-beams, directly achieving equal-gain dual beams. To extend this to equal-gain broadside and off-axis tri-beams, a novel analytical phase compensation approach is further proposed to mitigate the inherent gain degradation of off-axis beams. Guided by this method, a DBQP ten-beam array is 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 robust performance: axial ratios < 3 dB (25–30 GHz), cross-polarization levels < -20 dB (18–22 GHz), and peak aperture efficiencies >40% in both bands. This high-capacity architecture is a promising candidate for fixed-link, quasi-stationary nodes in future space–air–ground–sea integrated networks (SAGSIN).