Aircraft interception radar

Aircraft interception radar, or AI radar for short, is a historical British term for radar systems used to equip aircraft with the means to find and track other flying aircraft. These radars are used primarily by Royal Air Force (RAF) and Fleet Air Arm night fighters and interceptors for locating and tracking other aircraft, although most AI radars could also be used in a number of secondary roles as well.

Source: Wikipedia — Aircraft interception radar (CC BY-SA 4.0)