A Wideband 1-bit Reconfigurable Metasurface With Switchable Bidirectional Transmission and Reflection Modes

This article presents a novel wideband 1-bit reconfigurable transmit-reflect array (RTRA), which supports wideband beam-scanning capabilities in both transmission and reflection modes. A new bidirectional element is proposed, consisting of orthogonally oriented metallic polarization gratings on the top and bottom layers, with a reconfigurable cross-shaped bidirectional arrow resonator integrated in the middle. Four positive-intrinsic-negative (p-i-n) diodes are embedded within the reconfigurable resonator. By controlling the on/off states of the diodes, 1-bit phase modulation is achieved in transmission mode through Pancharatnam-Berry (PB) phase under polarization conversion, while in reflection mode, 1-bit phase modulation is realized via resonant phase under co-polarization. Moreover, the integration of the feeding structure with the polarization grating enhances the overall compactness of the elements. Then, a wideband characteristic with a relative operating bandwidth of 75% is achieved in both transmission and reflection modes. A 16× 16 array is designed based on the proposed element, and both simulations and prototype measurements are conducted. In transmission mode, beam scanning from 0° to 45° is achieved in both the E- and H-planes, with a maximum aperture efficiency (AE) of 19.1% and a 3-dB gain bandwidth of 38%. In reflection mode, beam scanning up to 45° is also demonstrated in both principal planes, with a maximum AE of 17.2% and a 3-dB gain bandwidth of 36.6%.