Abstract: In order to detect the target height in front of the vehicle, one transmitting and two receiving circularly polarized microstrip array antenna with high gain and low side lobe, which is applied to the 24 GHz automotive height measurement collision avoidance radar, is designed. The circular polarization characteristic of the antenna is realized by cutting angle on the square patch. By using the series-parallel hybrid feed network which is designed with the Dolph-Chebyshev synthesis algorithm, the high gain and low sidelobe characteristics are achieved. The measured results are in good agreement with the simulation results. The reflection coefficient and axial ratio of the circular polarization array antenna are less than -12 dB and 3 dB respectively in the frequency band of 24~24.25 GHz. At the center frequency of 24.125 GHz, the gain of the 10×4 element transmitting antenna and the 10×2 element receiving antenna are 22.5 dB and 19.5 dB, respectively. The azimuth side lobe is less than -20dB and the beam width of 3dB is about 9°, which meet the design requirements.