In this paper, we propose a novel method to increase the axial ratio bandwidth of a circularly polarized microstrip patch antenna. Demonstrated method consists of polarization dependent rectangular-shaped mushroom-like electromagnetic bandgap structures positioned around circularly polarized radiator patch. Since the structure itself has a polarization-dependent behavior, it was seen that a secondary minimum point can be introduced in the frequency dependency of axial ratio in main lobe direction. Additionally, increment in maximum gain is achieved as a result of natural characteristics of electromagnetic bandgap structures. Simulations made by HFSS show that axial ratio bandwidth can be increased using polarization-dependent electromagnetic bandgap structures. In this configuration, 3-dB axial ratio bandwidth can be broadened significantly.