Abstract: The antenna is an important part of the mine UWB positioning system. In order to suppress the multipath reflection signal received by the mine UWB positioning system and improve the positioning precision of the mine UWB positioning system, the traditional circularly polarized antenna structure is optimized. This study designs a new type of right-handed circularly polarized microstrip antenna. Firstly, the rectangular slot is changed to the cross slot. The current trajectory is changed to make the difference between the two orthogonal linearly polarized electric fields closer to 90°. The axial ratio is reduced to make the circularly polarized purity of the antenna higher. Secondly, the cross slot is smoothly expanded into a diamond slot to improve the cross-polarization level and suppress the orthogonal rotation. Therefore, the antenna can achieve higher right-handed circularly polarized purity. The HFSS software is used to simulate the new right-handed circularly polarized microstrip antenna. The simulation results show that the cross-polarization level in the main radiation direction is more than 10.4 dBi, which can achieve good right-handed circularly polarized effect. The measured results of the operating frequency band and echo of the new right-handed circularly polarized microstrip antenna sample are basically consistent with the simulation results. The results indicate that the new antenna structure is easy to be processed and the influence of the process deviation within the normal tolerance on the antenna performance is relatively small. The new right-handed circularly polarized microstrip antenna sample is used for the field test of the UWB positioning system based on the arrival phase difference in the tunnel environment. The test results show that the stability of the arrival phase difference of the signal is significantly improved. The multipath effect is significantly suppressed, which can effectively improve the positioning precision of the UWB positioning system. The new right-handed circularly polarized microstrip antenna has the advantages of small size, light weight and easy fabrication.