The application of adaptive frequency selective surface superstrate in the directive patch antenna

A adaptive frequency selective surface (FSS) superstrate for the directive patch antenna is proposed in this paper. The FSS superstrate is composed of periodic strips and cut wires loaded with tunable lumped-element capacitances. Based on the investigation of the transmission characteristic for its unit cell, it is found that the varying capacitance values can result in the shift of the transmission peak frequency of the designed FSS superstrate. The radiation performance of the proposed directive antenna is then analyzed. The simulation results show that the antenna gain is significantly improved by about 10 dB with introduction of the adaptive FSS superstrate for each selected capacitance value. The increase of the capacitance value makes the maximum gain location move towards lower frequency where the return loss is less than -10 dB. So the operation bandwidth of this antenna is indirectly enhanced.