Abstract: In order to improve the performance of the bandwidth of the microstrip antenna, a novel method for broadening bandwidth of the circularly polarized microstrip antenna is presented. Coaxial feeding loaded microstrip matching section is used to achieve impedance matching. The impedance and the axialratio bandwidths are improved by placing four sequentially rotated split-ring resonators around the patch of the antenna and embedding a defeated ground structure on the center of the ground plane. Experimental results show that the impedance and the axialratio bandwidths of the antenna are increased by 68.2% and 56.6%, respectively.

Key words: microstrip antenna , circularly polarized, split-ring resonator, defeated ground structure, bandwidth broadening