Characteristics of the basic PB unit cell. (a) Reflection magnitude of the basic unit cell under normal incidence of the LCP or RCP wave. Here, R_RR (R_LL) and R_LR (R_RL) represent the reflection magnitudes of co-polarization and cross-polarization under vertical radiation of LCP (RCP) wave, respectively. (b) Reflection amplitude and reflection phase under normal incidence of the x-polarized and y-polarized waves.