Effective Reflective Characteristics of Superstrates and Their Effects on the Resonant Cavity Antenna

Aiming at exploring the basic functional mechanism of superstrates in the resonant cavity antenna (RCA), two popular superstrates, i.e., the homogeneous dielectric superstrate and the periodic microstrip superstrate are investigated. Their reflection coefficients to normal and oblique plane wave incidences are studied by using mathematical derivation and simulations. Based on it, their effects on performances of the RCA are analyzed through simulations and measurements. Results show that, despite of different configurations, the superstrates can be purposely engineered to have the same reflection coefficients, which results in the same improving effect on the RCAs broadside gain, radiation patterns and, more interestingly, broadening effect on the return loss bandwidth. The research demonstrates the key role of their effective reflective characteristics in the RCA, and can inspire more advanced superstrates for RCA designs.