How fighter jets lock on, and how the targets know (2014)

The primary technology that a military aircraft uses to lock and track an enemy aircraft is its onboard radar. In search mode, no single aircraft is being tracked, but the pilot can usually tell generally what a particular radar return is doing because with each successive sweep, the radar return moves slightly. What about missiles? Again, a radar lock is not required. For heat-seeking missiles, a radar lock is only used to train the seeker head onto the target. Passive radar missiles do require a radar lock, because these missiles use the aircraft's reflected radar energy to track the target. Although an aircraft's radar can only scan out in front of the aircraft, an aircraftcan listen for incoming radar signals in any direction, so the scope is 360°. Aside from radar, there are other technologies that are used to lock on to enemy aircraft and ground targets.