Design of high gain, wideband microstrip resonant cavity antenna using FSS superstrate with equivalent circuit model

Abstract

A high directivity wideband resonant cavity antenna (RCA) is proposed in which a compact wideband microstrip patch antenna (MPA) is utilized as radiator. Through introducing an interdigital capacitor (IDC) in the patch, a planar metamaterial (MTM) unit cell in the ground plane and cutting two vertical slits from the slot, size reduction of the radiator is realized. To improve the directivity of the proposed MPA, a wideband FSS superstrate is designed and placed above the MPA making the whole antenna to operate as RCA. By using image theory, even and odd modes in RCA are analysed and the distance between FSS and the radiator is adjusted leading to optimum directivity and bandwidth in the proposed RCA. Maximum directivity enhancement in the designed RCA compared to the single element radiator is 4.2 dBi in the impedance matching bandwidth. The measured bandwidth and maximum gain of the proposed RCA are 24.9% and 11.2 dBi, respectively. Additionally, an equivalent circuit model for MPA and designed RCA is developed. The proposed antenna exhibits high gain and low cross polarization level making it a good candidate for radar applications. The final designed antenna is fabricated and the measurement results agree well with the simulation results.