Lock-on is a feature of manyradar systems that allow it to automatically follow a selected target. Lock-on was first designed for theAI Mk. IX radar in the UK, where it was known aslock-follow orauto-follow. Its first operational use was in the US ground-basedSCR-584 radar, which demonstrated the ability to easily track almost any airborne target, from aircraft to artillery shells.
In the post-WWII era, the term became more widely used in connection tomissile guidance concepts. Many modern anti-aircraft missiles use some form ofsemi-active radar homing, where the missile seeker listens for reflections of the launch platform's main radar. To provide a continuous signal, the radar is locked-onto the target, following it throughout the missile's flight. Ships andsurface-to-air missiles often have a dedicatedilluminator radar for this purpose.
In older radar systems, through the 1980s, lock-on was normally assisted by a change in theradar signal characteristics, often by increasing thepulse repetition frequency. This led to the introduction ofradar warning receivers that would notice this change and provide a warning to the operator.[1]
Modern radar systems do not have a lock-on system in the traditional sense; tracking is provided by storing radar signals incomputer memory and comparing them from scan to scan using algorithms to determine which signals correspond to single targets. These systems do not change their signals while tracking targets, and thus do not reveal they are locked-on.
With asemi-active radar homing system, the launch platform acquires the target with its searchradar. The missile is then powered up while the launch platform's illuminator radar "lights up" the target for it. The illuminator is a radar transmitter with a narrow, focused beam that may be separate from the search radar and that can be directed at a target using information from the search radar. When thepassive radar of the missile's guidance system is able to "see"/detect the radio waves reflected from the target, missile lock-on is achieved and the weapon is ready to be launched.[2]
The subject of a radar lock-on may become aware of the fact that it is being actively targeted by virtue of the electro-magnetic emissions of the tracking system, notably the illuminator. This condition will present a heightened threat to the target, as it indicates that a missile may be about to be fired at it.