IFF (Identification Friend or Foe) is the military designation for the Air Traffic Control (ATC) System that is used to identify and track military aircraft. The IFF system consists of a ground (or airborne, or shipborne) interrogator and an airborne transponder. The interrogator transmits a coded interrogation burst via a directional antenna, to which the airborne transponder replies with identification information according to the type of interrogation. The interrogator then determines the range and bearing to the target. Depending on the type of interrogation, the transponder may encode altitude, position, and other pertinent flight information.