This paper presents two compact slot array antennas for the 79 GHz automotive bintegrated into a 28 µm thick benzocyclobutene (BCB) substrate attached to a 325 µm thick 5€“20 Ω cm bulk resistivity silicon wafer. The two antennas are a transmit (TX) 1 × 8 slot array antenna with a size of 1 × 23 mm a receive (RX) 8 × 8 slot array antenna with a size of 15 × 23 mm. Promising performance has been measured with the TX RX subarray antennas (gain >4 dBi) with good matching to 50 „¦ (RL > 10 dB) in the frequency range 70€“90 GHz. By using a metal cavity, mounted on the back of the antenna, potential parallel plate or cavity modes could be reduced the gain could also be increased by 2 dB. The measured the simulated results are consistent._x000D_