Design of broadband slot antennas for circular polarization

It is well-known that the circular polarization (CP) bandwidth of a microstrip antenna is greatly related to its impedance characteristic. Several broadband antenna structures have been proposed and studied, such as using a thick substrate with low permittivity and a multi-resonator structure. Another method to enhance the impedance bandwidth is using slot antennas instead of the microstrip antennas. In this paper, a new CP design developed from the ring slot antenna is proposed. The antenna structure composed of a wide slot and a parasitic patch is with wideband characteristics. By adjusting the distance between the wide respectively, which are obviously higher than that of a same-size microstrip antenna. Also, the CP designs of wide slot antennas have been investigated to further improve the CP bandwidth. By protruding a T-shaped [3] or an L-shaped strip [4] from the ground plane, the CP bandwidth of the wide slot antenna can reach to 18 %. However, the available designs for the slot antenna with more than 20 % CP bandwidth are relatively few in the open articles. In this paper, a new CP design developed from the ring slot antenna is proposed. The antenna structure composed of a wide slot and a parasitic patch is with wideband characteristics. By adjusting the distance between the wide slot and parasitic patch, the CP bandwidth can be varied between 5 and 45%. Details of the proposed designs and the obtained results are shown and discussed.