Analysis and design of a 1-bit circularly polarized reconfigurable transmitarray for bandwidth and efficiency...

Spin-decoupled strategy is essential for ensuring broad axial ratio (AR) bandwidth in circularly-polarized (CP) metasurfaces. However, existing CP metasurfaces based on discrete phase mostly suffer from narrow AR bandwidth and low aperture efficiency due to insufficient rotational phase. In this work, what we believe to be a novel 1-bit CP reconfigurable transmit-array (TA) is proposed to simultaneously improve AR bandwidth and aperture efficiency. First, the key constraint on the AR bandwidth of 1-bit CP arrays is analyzed based on the theoretical derivation. Then, an orthogonal element array is proposed to break the 1-bit phase patterns correlation between the co- and cross-polarization, preventing the codirectional cross-polarized beam. Next, an optimum design is presented to enhance the gain and AE by constituting an array with localized blocks. Furthermore, a 1-bit reconfigurable CP element with a tunable radiation layer is designed, along with an array composed of the cells and an optimized layout, excited by a planar CP feed source. Compared to the reported 1-bit TAs, the AE of the CP beam of the proposed array is increased to 24.4% at 10 GHz, approaching that of some 1-bit RAs and even continuous-phase arrays. The gain variation < 3 dB and AR < 3 dB relative bandwidths are superior to 21.1% and 30.8%. Finally, the optimized 1-bit CP TA is designed, manufactured, and measured. The measured results are in good agreement with the simulations, achieving wide-angle beam scanning of ±60° with goodish gain and bandwidth performance.