Radar is an acronym which stands for "Radio Detection and Ranging". It comprises both different methods and devices for the detection and localization of objects through electromagnetic waves. A radar device emits bundled electromagnetic waves (the so-called primary signal), often in the form of strong, high-energetic pulses, which cause reflections at the object to be detected. These echoes are received as a secondary signal and evaluated according to different criteria and methods. Information gained by the secondary signal are e.g. angle, distance and relative speed between the radar device and the reflecting object.
Generally, a distinction between primary and secondary radar systems can be made. While primary radar systems exclusively receive the passive echoes of initially emitted radiation, secondary radar systems analyze active signals, i.e. signals emitted by the detected object itself. Consequently, primary radar systems work with higher power than secondary systems to guarantee that the signal attenuated by reflection is still being received.