Abstract: This paper introduces a compact microstrip double-antenna array applied to millimeter wave radar front-end with transmitter and receiver separately.The double-antenna includes two 4-element microstrip antenna arrays with parallel feed which both lay on a circular substrate with 18.6mm diameter and act as receiver and transmitter antennas respectively.The radar front-end circuit employed MMIC chips is integrated on the substrate with the same shape as the antenna with MCM technique and connects with the antenna from back to back,couples energy through holes coupling.Experiments results show that the double-antenna provides gain of 10.5dB and isolation between two antennas better than-34dB.The radar front-end has perfect performance.