Design of a Small-Size Broadband Circularly Polarized Microstrip Antenna Array

A small-size 2×2 broadband circularly polarized microstrip antenna array is proposed in this article. The array has four broadband dual-feed U-slot patch antenna elements with circular polarization, and the sequential feeding technique is used to further enhance the 3 dB axial ratio bandwidth. The lateral size of the fabricated array is as small as 1.33λ0×1.33λ0, and the profile is only 0.04λ0. Measured results show that the overlapped -10 dB reflection coefficient and the 3 dB AR bandwidth is 53%, and the variation of the measured realized gain is less than 1 dB for S-band satellite communications (1.98-2.2 GHz).