Why pulse compression works
Pulse compression, sometimes called matched filtering, is a technique for extracting information about a signal based on knowing what that signal is. Frequently used in radar, sonar, and photonics, pulse compression is particularly useful in suppressing noise and improving the accuracy of range finding.
In any active ranging system, whether it be radar, lidar, or sonar, a signal is broadcast from a transmitter and reflected off of objects in the far field. The return signal is then received, usually at the same site but sometimes elsewhere, and processed.
A common early method of range finding was to use pulses of a single frequency or tone. This is the well-known “ping” from submarine movies. In the early days of radar during the battle of Britain, for example, radar would be sent in pulses that swept across a circular area. In between pulses, the radar would listen for the echoes from distant objects and those echoes would be translated into blips on a cathode ray tube display. Many modern radars still mimic these old displays despite using vastly more advanced technology.
These single tones had to be relatively short in duration. Consider that if two objects, such as airplanes, were close together, the echoes from the two would overlap one another. This would make it look as though the aircraft were one large object instead of two.
