Abstract: Based on Rogers 5880 dielectric material, a radar front-end circular polarization microstrip antenna array for the vehicle collision avoidance system is designed, which adopts linear array structure and many quarter wave impedance converters to achieve impedance matching. Simulation and test results show that the impedance bandwidth of the antenna array (S₁₁ < -10 dB) is from 23.45 GHz to 25.65 GHz, the biggest gain is 15.54 dB; and the AR(axial ratio) bandwidth is from 24.56GHz to 25GHz, the minimum AR is 1.25 dB. The first sidelobe level is -20 dB, E-plane half power beam width is 10°, H side lobe width is 75°, and the size of the dielectric material is 70.94 mm×14.72 mm×0.508 mm. With the advantages like high gain, low side lobe, small size, and stable performance, the practicability of array antenna is verified and it may be widely applied in automobile anti-collision radars.