A novel broadband circularly polarised waveguide slot array antenna with a wide axial ratio bandwidth

In this study, a novel broadband circularly polarised waveguide slot array antenna with a wide axial ratio bandwidth is designed. The circular polariser is excited by the waveguide radiation linear polarised antenna, whose end is bent by 90 degrees and generates a circularly polarised electric field. The matching waveguide between the slot and the polariser improves impedance matching. Furthermore, the structure with the added waveguide changes waveguide impedance, which can be used to realise impedance matching, and reduces the spacing between the units. In this study, a 4 x 4 antenna array is fabricated. The measured results reveal that the array achieves -10 dB impedance bandwidth of 27% (11.15-14.63 GHz) and the 3 dB axial ratio bandwidth of 23% (11.48-14.52 GHz). An aperture efficiency higher than 71% is obtained, with the maximum gain of 22 dB. The antenna side lobes levels are less than -13 dB in the operating bandwidth.