Independently In several countries as a military Instrument for detecting aircraft and ships. One of the earliest practical radar systems was created from 1934 to 1935 by Robert Watson-watt. Although the technology evolved rapidly during World War II, the radar Improved Immensely following the war, the principal advances being higher power outputs, greater receiver sensitivity, and improved timing and signal-processing circuits.
In 1946 radar beams from the earth were reflected back from the moon. Radar contact was established with Venus in 1958 and with the sun in 1959, thereby opening a new field of astronomy called radar astronomy Radar involves the transmission of pulses of electromagnetic waves through a directional antenna. Some of the pulses are reflected by objects that intercept them. The reflections are picked up by a receiver, processed electronically, and converted into visible form by means of a cathode-ray tube.
The range of the object Is determined by measuring the time it takes for the radar signal to reach the object ND return. The object’s location to the radar unit Is determined from the direction In which the pulse was received. In most radar units the beam of pulses Is continuously rotated at a constant speed, or it’s scanned over a sector, also at a constant rate. The velocity of the object is measured by applying the Doppler principle The information secured by radar includes the position and velocity of the object with respect to the radar unit.
In some advanced systems the shape of the object may also be determined. Commercial airliners are equipped with radar devices that warn of obstacles in or approaching their path and give accurate altitude readings. Planes can land In fog at airports equipped with radar-assisted ground-controlled approach systems, In which the plane’s flight Is observed on radar screens while operators radio landing directions to the pilot. A ground-based radar system for gulden and landing aircraft by remote control was developed In 1960.