Design of Compact Circularly Polarized Antenna Using Sunshine-Shaped Slotted Patch

We propose a method to design compact circularly polarized (CP) antenna using a novel sunshine-shaped slotted radiating patch, which exhibits slow wave and other interesting properties. The structured radiating patch introduces adjustable coupling between a pair of orthogonal modes (TM10 mode and TM01 mode) to facilitate good axial ratio (AR) and reflection parameters of the antenna simultaneously in the radiating frequency band. A $\pi $ /2 balun is employed to excite the TM10 and TM01 modes by using back feeding structure. Based on the proposed method, a compact left-hand CP antenna is designed, fabricated, and measured to verify the feasibility of the design method. The whole antenna is $0.17\lambda _{0}\times 0.17\lambda _{0}$ in dimension ( $\lambda _{0}$ is the wavelength in free space) and the measured maximum gain is 5 dBic in the working band, and 3 dB AR bandwidth is 0.4% for left-hand CP.