New coplanar capacitively coupled feeding method for circularly polarized patch antenna

A new coplanar capacitively coupled feeding method for circularly polarized patch antenna is developed and discussed. The circular polarization (CP) radiation of the square patch antenna is achieved by a parallel short-ended microstrip line. A prototype has been designed and simulated and found to have an impedance bandwidth of 5.3% and a 3 dB axial-ratio bandwidth of about 1.2% at the center frequency of 2250MHz. The coupling mechanism can be approximately considered as a microstrip coupled line directional coupler, which is simple and flexible to obtain circular polarization without any alteration to the microstrip radiator such as truncating the corner and add-on slits. This single-feed circular polarization could be achieved by only adjusting the microstrip feed lines, which is independent of the square patch radiator. The proposed capacitively coupled feeding method has a coplanar structure and adequate CP bandwidth such that is suitable for a wide range of circularly polarized microstrip antenna applications.