Single-patch broadband circularly polarized microstrip antennas

The authors present a new design of a single-patch broadband circularly polarized microstrip antenna with dual capacitively-coupled feeds connected to a Wilkinson power divider having a 90/spl deg/-phase shift between its two outputs. A thick air substrate is used in the present proposed design, and impedance matching is obtained through capacitive coupling between the two feeds and the radiating patch. A design example of the proposed antenna with a circular radiating patch has been implemented, and experimental results show that, with the distance between the radiating patch and the ground plane being less than 10% times the center operating wavelength, the proposed antenna can have an impedance bandwidth greater than 50% and a 3-dB axial-ratio bandwidth about 34%. The antenna gain bandwidth, defined to be within 1-dB gain variation in the axial-ratio bandwidth, is 29%, with the antenna gain level about 7.0 dBi. Details of the proposed antenna design and experimental results are presented and discussed.