In the post-WWII era, the term became more widely used in connection to
missile guidance concepts. Many modern anti-aircraft missiles use some form of
semi-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 and
surface-to-air missiles often have a dedicated
illuminator radar for this purpose. In older radar systems, through the 1980s, lock-on was normally assisted by a change in the
radar signal characteristics, often by increasing the
pulse repetition frequency. This led to the introduction of
radar warning receivers that would notice this change and provide a warning to the operator. Modern radar systems do not have a lock-on system in the traditional sense; tracking is provided by storing radar signals in
computer 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. == Types ==