How a radar works is the way a bat navigates at night without seeing anything but hearing its own echoes of the squeaks it sends forwards. The sound of the sharp squeaks bounces off objects and comes back. Then the flying bat picks it up with its sensitive ears and then it knows the way through which it must fly without crashing against houses, walls, mountain crags, or lamp posts. Thus, how a radar works is simple, like a bat's navigation system. Bats are extremely short-sighted as they have atrophied vision but they have the sharpest hearing in nature.
Nearly all radars work by sending out a stream of pulses made up of short radio waves. These pulses reflect off objects and the radar detects them on their return. Since radio waves travel through the atmosphere, at a constant and very high speed, the short time interval between pulse and reception measures the distance to the radar target. A radar system consists of a pulsing source of electrical energy, which is coupled to an antenna that emits corresponding radio pulses in a more or less well defined beam, and a receiver to detect the returning echo. This receiver is another antenna that picks up the incoming echo. The receiver is linked to a display device for the human eye to observe it on a screen.
All of the major radar functions can be reduced to the determination of the range and bearing (direction) of an unknown target. The latter is very much the matter of how sharply the sending and receiving antennas shape radar beams. At least one of the two must be highly directional, otherwise the radar cannot know from which direction an echo originates. Although today modern radars use one complex antenna, during World War II, the British Navy's radars required separate antennas.
How fast radio waves travel
The measurement of the range to a target is a matter of precisely measuring time. Radio waves travel at 328 yards every microsecond; that is to say they travel 328 yards per one millionth of a second. Since the time in question is the time between transmission and reception, the radar pulse must make the journey to and from its target, which means that every microsecond represents 164 yards of range. It seems remarkable in retrospect that the accurate measurement of such short times was one of the least difficult problems in radar development.
Below, a Selenia RAN-3L search radar antenna on an Italian Navy's ship in the 1960s.
