Directivity-enhanced log-spiral antenna through a chiral metamaterial superstrate

A systematic method to enhance the performance and radiation characteristics of circularly-polarized antennas, by using a chiral metamaterial superstrate, is presented in this paper. The novel structure consists of a log-spiral radiator, backed by a properly placed reflector and a superstrate involving a periodically-repeated pattern of chiral resonators, sufficiently covering its radiation area. The selected antenna is modified for wide-band operation in order to reveal the advantages of the proposed superstrate. For the characterization of the resulting structure, a comprehensive investigation by means of a flexible finite-difference time-domain method is conducted. Numerical results prove the considerably improved directivity, thus revealing the efficiency of the concept for potential applications.