Axial ratio measurements of circularly polarised antennas based on polarisation rotation

In the study, an improved method for measuring the axial ratio of circularly polarised antennas based on the polarisation rotation is proposed. In the measurements, an auxiliary antenna can work in different rotation senses of polarisation (left-hand or right-hand) according to the status of the antenna polariser. By measuring received signals of the circularly polarised antenna under test when the auxiliary antenna work in the left-hand or right-hand modes at two different axial angles, the axial ratio of the antenna under test can be determined from the polarisation efficiency equations. The measurement of a typical circularly polarised antenna is performed in the anechoic chamber by using this method. Through the comparison between the measured results and the simulation results, the validity of this method is demonstrated. This method improves the measuring efficiency and has important engineering application.