On the Design of Linear to Circular Polarization Converter based on FSS

In this paper, a Frequency selective surface (FSS) based polarizer is proposed to convert the linear polarization (LP) into circular polarization of an antenna. The polarizer is a two layer structure with variable size unit elements. The lower layer of the polarizer consists of split ring as a unit element while the upper layer has a simple rotated dipole as a unit element. The polarizer is used as a reflector for a Coplanar Waveguide (CPW) fed LP antenna. The polarization conversion is done for dual band namely 3.5 GHz communication and Unlicensed National Information Infrastructure (UN-NII) low band. The antenna with the polarizer has 3 dB Axial Ratio Bandwidths (ARBW) of 0.5 GHz (3.5-4.0 GHz) and 0.29 GHz (4.98-5.27 GHz) in boresight direction. Additionally the boresight gain of the antenna is increased by 4 dB. Also the co-polarization to cross-polarization ratio is increased by more than 15 dB in the boresight direction in both the bands. The polarizer along with antenna is fabricated and tested. The simulation and the experimental results are both in good agreement.