Broad-band single-patch circularly polarized microstrip antenna with dual capacitively coupled feeds

New design of a circular microstrip antenna with dual capacitively coupled feeds for broad-band circular polarization radiation is presented. The dual feeds are with a small top-loaded disk and are connected to a Wilkinson power divider with a 90/spl deg/ phase shift between its two output feedlines. The radiating circular patch, printed on a thin substrate, is supported by nonconducting posts on a conducting ground plane and is excited capacitively through the dual feeds. With a distance less than 10% times the center operating wavelength between the circular patch and the ground plane, the present proposed antenna can provide an impedance bandwidth (VSWR /spl les/2) of about 49% and a 3-dB axial-ratio bandwidth of about 35%. The antenna gain bandwidth, defined to be within 1-dB gain variation in the axial-ratio bandwidth, is as large as 28%, with the antenna gain level at about 7.0 dBi.