A circularly-polarized (CP) antenna based on coupled resonators with simple structures and stable CP performance is proposed for applications on wearable devices. It is found that two identical coupled monopole antennas on a square ground can be equivalent as a second-order circuit network based on J/K inverters. Two coupled resonators can generate a pair of even and odd modes. Their resonant frequencies are determined by the coupling strength k. Characteristic mode analysis (CMA) is conducted to verify the proposed circuit network. It reveals that the even and odd modes of the proposed structure are candidates for CP radiation. In conclusion, the proposed antennas have the advantage of insensitivity to perturbation segments. Hence, they can maintain stable CP performance, which is highly demanded in wearable devices. Measurements under different situations reveal that the CP antenna has high and stable position accuracy.