Directivity enhancement of circularly polarized microstrip antenna using split ring FSS superstrate

In this paper, a spit ring frequency selective surface is designed to enhance the directivity of a circularly polarized aperture coupled microstrip antenna. In order to characterize the radiation parameters of the proposed structure, a simple ray tracing method is used. It was investigated through simulation that polarization dependent frequency selective surfaces are more capable of reducing the cross polar radiation components, so we have used polarization dependent FSS for this design. In order to achieve circular polarization, we have used two oppositely polarized FSS unit cells so as to nullify the effects of their polarization dependency. Simulation results show that the proposed structure achieves a broadside peak gain of approximately 14 dB for the entire frequency range where the axial ratio is less than 3 dB.