Stacked Open-Loop Square Ring Antenna for Circular Polarization Operation

In this letter, a novel circular polarized (CP) open-loop square ring antenna using a stacked structure is proposed. The proposed antenna consists of two open-loop square ring resonators and a T-shaped feed structure. The resonant frequency of the ring resonator is adjusted mainly by changing the width of the ring. Depending on the location of the gap in the square ring, each open-loop square ring antenna exhibits different linear polarizations. By selecting a suitable ring width and gap position, two orthogonal resonant modes with equal amplitude and a 90
^°
phase difference are excited, and good CP is achieved. The measured 10-dB reflection coefficient and 3-dB axial ratio bandwidth of the antenna prototype are 3.93% and 1.2%, respectively.