Novel circularly polarized slot array antennas with a wide 3-dB axial ratio bandwidth based on a spindle-shaped radiating cavity

A novel wide 3-dB axial ratio (AR) circularly polarized 2 x 2 array antenna is proposed in this paper. The spindle-shaped coupling cavity with tilted waveguide is capable of generating circular polarization waves from incident linear waves, which improves the AR bandwidth (ARBW) of the antenna. With this structure, a similar amplitude of the two orthogonal transmitted wave components and a stable phase difference of nearly 90 degrees can be generated. The circularly polarized antenna proposed herein has been fabricated. According to the measurement results, the operating bandwidth from 5.32 to 6.13 GHz is <-10 dB. In addition, the measured ARBW, which is below 3 dB, can cover the range of 5.41-6.02 GHz. The maximum gain of the antenna can attain 15.65 dBi, and the efficiency is better than 80%.