This paper describes and analyzes a new technique used in Q-slot antenna to generate circular polarization (CP). The CP characteristics were investigated carefully by studying the surface current distribution, the phase difference between the left hand circular polarization (LHCP) and right hand circular polarization (RHCP) at some resonant frequencies, and the measured values of the axial ratio bandwidth (ARBW). Normal arms (E1 and E2) were cut in the upper elliptical feeding strip line to form an open-mouth structure. The arms E1 and E2 were made equal in length and set perpendicular to each other to have normal electric fields, leading to the generation of CP radiation. A formula was modified for the dual resonant frequencies f1, f2 of the modes TM010 and TM001. The measured values of the ARBW indicated that the antenna has a wide ARBW of 4.8–5.93 GHz, which is approximately 52% of the 3rd operating band of 4.7–6.8 GHz. The wide ARBW in a small size indicated that the design of the Q-slot antenna overcame the limits of designing antennas with wide ARBW in small size and low profile. A formula for normalized field was driven according to the complementary of the Q-slot antenna.