Design of a Wideband Dual-Feed Circularly Polarized Antenna for Different Axial Ratio Requirements

A novel method of designing a wideband dual-feed circularly polarized (CP) antenna is presented for different axial ratio (AR) requirements. By analyzing the output characteristic of the feed network for the dual-feed CP antenna, an approximate function is obtained and utilized to calculate the variances of the output magnitude and phase of the feed network under a required AR. Based on the analysis, different branch-line couplers are used for achieving wide AR bandwidths of less than 3, 2, and 1 dB, respectively. Compared to the traditionally used 3 dB coupler, the presented feed method can have an AR peak with the expected value at the center frequency and two AR valleys beside the peak, while the traditional 3 dB coupler can only get an AR valley with narrower bandwidth. Therefore, much wider AR bandwidths for different AR requirements are obtained by using the presented method. The wideband dual-feed antenna fed by these different couplers was simulated, fabricated, and measured for the final performance verification.