The Development of Radar

The invention of radar can be traced back to experiments with radio waves carried out by physicist, Heinrich Hertz (1857-1894). Hertz discovered that radio waves passed through some materials and were reflected by others. In 1904, scientist Christian Hulsmeyer showed that radio waves could detect ships, and

О Dish antennae such as these at a tracking station in California swivel to pick up signals.

he suggested that this ability might be used to avoid collisions at sea, but there was no interest in his idea.

In 1922, the effect was rediscovered when a ship on the Potomac River in Washington, D. C., caused a disturbance to radio signals being sent across the river. An airplane was detected by radar for the first time in 1930.

As World War II approached, scien­tists in Britain and Germany stepped up their research into radar. The first prac­tical radar system for air defense was developed in Britain by Sir Robert Watson-Watt in 1935. During the war, the British coastline was protected by a system called Chain Home. When the system detected approaching aircraft, the planes’ positions were plotted on a map in a control room. Fighter pilots

were then given instructions by radio to guide them toward the incoming enemy aircraft. Germany also developed an air defense radar system, called Freya, dur­ing World War II. In addition, radar was also used to guide searchlights and anti­aircraft guns.

These early radar systems were too big and heavy to install in an aircraft. In 1939, however, scientists at Birmingham University, England, invented a device called a cavity magnetron, which enabled radar equipment to transmit and receive much shorter radio waves. This made it possible to build smaller and more powerful radar equipment, light enough to be carried by aircraft. As they developed, these systems had been known as RDF (radio direction finding). In 1942, the term radar (short for radio detection and ranging) came into use.

In 1943, British bombers were equipped with a radar system named H2S. It pointed downward and showed a map of the ground on a screen inside the aircraft. It enabled bombers to find their targets through the cloud cover. An improved U. S. system called H2X was developed in 1945.