A new method for broadening the impedance and the axial-ratio (AR) bandwidths of circular polarized microstrip antennas (CPMAs) is proposed. It has improved the bandwidths of a reference antenna greatly without enlarging the antenna size or deteriorating circular polarized radiation characteristics by placing four sequentially rotated parasitic split-ring resonators (SRRs) around the patch of the reference antenna and embedding four defeated ground structure (DGS) elements on the ground plane. Improvements of 51.3% and 49.8% in the impedance and the axial-ratio bandwidths of the antenna are achieved in simulation, respectively. The simulated -10dB impedance and 3dB axial-ratio bandwidths of the antenna have been improved from 101.1 MHz (4.12%) to 153.0 MHz (6.26%) and from 25.1 MHz (1.02%) to 37.6 MHz (1.54%).
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