Airborne Warning and Control Systems (AWACS) system consists of a radar mounted on airplane. This radar releases ultrasonic waves in all the directions. Any incoming object in airspace such as aircrafts, missiles, etc reflect these waves back to the radar, signalling the presence of object.

India already has three operational Phalcon AWACS. These AWACS were purchased from Israel. These AWACS are radars mounted on IL-76 (Ilyushin plane which was delivered by Russia.) 

The govt. has decided to procure to more AWACS from Israel.

All the best!