Within its range it can show an observer ships, planes , storm clouds, small islands, coastlines , and prominent landmarks. It can also be used to measure the distance to an object and the speed at which the object is moving toward or away from the observer. Radar was developed from the work of many scientists. Discoveries made by Heinrich Hertz, Karl F. Braun, and Christian Hulsmeyer of Germany, Guglielmo Marconi of Italy, and Lee De Forest of the United States laid some of the foundations. Robert Watson-Watt of Scotland patented a radar system in 1935.
Radar uses electromagnetic waves usually short-wavelength waves called microwaves.
These waves bounce back from solid objects in their path, the way sound waves bounce back from an object and produce an echo. Scientists learned to use reflected microwaves for detection and measurement. A radar set with its antenna both transmits and receives. In the most widely used type of system, wave bursts, or pulses, are spaced so that the echo from one pulse is received before the next pulse goes out. For example, a set may be designed for a range of 93 miles.