A Feeding Technique for Wideband CP Patch Antenna Based on 90° Phase Difference Between Tapped Line and Parallel Coupled Line

Abstract

A feeding technique for wideband circularly polarized (CP) patch antenna based on the 90° phase difference between tapped line and parallel coupled line in a feeding network is proposed. The tapped line and parallel coupled line are equivalently regarded as a direct coupling element with 0° phase delay and a J -inverter coupling element with 90° phase delay, respectively. In design, two identical λ /2 resonators are employed to excite two orthogonal modes for wideband equal magnitude. Meanwhile, the feeding lines are tapped and coupled to the two resonators, and tapped line and coupled line can inherently provide 90° phase difference as demanded for CP radiation with no need for an additional delay line or a phase shifter. The whole structure is modeled as an equivalent three-port network, and the theoretical axial ratio (AR) is calculated with the magnitude and phase of the voltage at the radiation conductance. Since two minima in AR response emerge, this proposed patch antenna can achieve a wide AR bandwidth. The theoretical performance is finally verified by a fabricated CP patch antenna prototype with a profile of 0.042 λ 0, and the 3 dB AR fractional bandwidth is 7.07%.