A dual-feed circularly polarized patch antenna based on Substrate Integrated Coaxial Line(SICL) feed is proposed. Dual-feed point method is utilized to realize circular polarization. With the backed cavity, the antenna performance, for example, the bandwidth, the back lobe, the mutual coupling and the structure miniaturization, has been improved. Simulation results show that the antenna can achieve S11<-10 dB(relative bandwidth is 28.8%@51 GHz) at 42.42~56.69 GHz, and the axial ratio is less than 3 dB and the maximum gain is 8.9 dBi at 45.26~48.08 GHz.