The story of radar begins first with radio. Without radio, radar would never have been possible. Today, radar is a standard piece of equipment used in many forms and ways and something most people have heard of. Before the Second World War though, radar technology was regarded as a top secret project by the nations that were rapidly discovering it.

Radar = RAdio Detection And Ranging.

Flight Radar First Discovery

The first time radar was really discovered was far back in the 19th Century by a German scientist called Heinrich Hertz. He discovered that radio waves reflected off of metallic objects. This followed work through radio in electromagnetism.

The first practical use of object detection using radar methods came early in the 20th Century when Christian Hülsmeyer built a very simple system to detect ships through the fog. It was over the next two decades that radar and the advancement of it really gained traction. Like many technological advances, the primary catalyst for this traction was war.

Military Applications Lead to Radar Advancement

The First World War was the catalyst for rapid advances in aviation. Many nations in Europe recognised this and military strategists became very aware of a need to track and measure aviation movement for defence reasons. This started off with experiments using “sound mirrors” which used a radar dish with a microphone to detect the sound of engines at longer distances. Robert Watson-Watt invited Air Chief Marshal Hugh Dowding for a demonstration. Unfortunately, it didn’t go well as a passing milk float completely disrupted the demo. Watson-Watt quickly decided that using sound to detect aircraft wasn’t the most reliable way of doing things! Following investment from the British Government to, rather bizarrely, research radio “death rays”, radar was soon chosen as the way forward.

As the Second World War began in 1939 a network of transmitter and receiver radar stations were set up along the south coast of England named “Chain Home”. This system was the primary defence aid, other than relying on the most excellent, but limited, observer corps who relied solely on their eyes and ears.

Poley radar station
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The feedback provided by these early radar types was very different from the radar screens we know and are familiar with today.

Early radar scope
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The radar controller would see pulses rise on a Cathode Ray Tube (CRT) scope whenever an echo or reflection was seen indicating an object. The transmission pulse would start at “0” on the scale and the return pulses would be seen along a ruler indicating distance. For example, if a return pulse was seen at ‘50’ that meant the target or object was 50 miles away.

Early radar echo diagram
© 2012

By June 1940 PPI (Plan Position Indicator) was also available providing a top down view. This enabled the bearing of aircraft approaching the radar stations to be provided. This was achieved using another transmitter that rotated and transmitted radio waves in azimuth range (a thin, vertical transmission of radio waves which rotates around 360 degrees and detects echoes vertically rather than horizontally). Not only could the UK’s Fighter Command now see the distance and the speed of incoming enemy aircraft, they could now provide bearings. This was a key advantage and meant that RAF Squadrons could be immediately scrambled and provided with accurate directions and information on where the enemy aircraft were.

Early radar scope plan view
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Originally, Radio Detection Finding (RDF) was the term coined to describe this technology until in 1940 when the US Navy coined ‘radar’ as we know it today using the acronym stated above. At the time, this technology was regarded by all nations involved in working with it as highly top secret.

After the Second World War

Things in Germany came to a halt after the Second World War regarding advancements in radar. The US, the UK and the USSR all hired the German engineers and technicians to work on their own radar systems.

One of the more important advances in the use of radar was developed by the UK’s Royal Air Force. This was using radar to assist in landing aircraft with reduced visibility onto runways. Today, this has developed into the system known as the Instrument Landing System (ILS) and can be found on most aerodromes and airports around the world today.

Throughout the late 1940’s and through the 1950’s radar continued to be developed. This paved the way for more mature radar methods:

  • Pulse-Doppler radar (better detected moving objects through clutter caused by animals and weather conditions)
  • Monopulse radar (this increased tracking accuracy)
  • Phased-array radar (allowing simultaneous tracking of multiple targets)

During the Cold War between the US and the Soviet Union, American technology in radar steadily increased as they deployed multiple, massive networks of radar across the west coast and Canada to form an early warning system. By the late 1940’s both the US and the Soviet Union had aircraft that could carry nuclear weapons which inspired the need for these large warning systems.

Radar works using ‘line of sight’; transmissions that are sent in straight lines. This means that the transmission waves hit anything in their path and return an echo. This includes terrain which can cause ‘radar shadows’ blocking out sections of the radar scope. This is because the ground absorbs the radio transmission rather than reflect them leaving no echo to be received at the receiver. In the 1950’s it was discovered that radio waves could be bounced off the ionosphere and still received back to the transmitter. This allowed signals and radar to reach beyond the limits that terrain caused.

By the 1970’s radar had reached much higher wattage allowing radar transmission of much higher intensity. This allowed echoes to be detected from higher distances. The system known as ‘Arc’ in Russia could detect a missile launch at 1,600 miles, it was estimated to have a power of about 10 Mega Watts. Radio amateurs code named it “Woodpecker” as they regularly received interference caused by this very powerful radar installation.

Satellite brought a new technology to the table that then played a part in modern day radar systems using ADS-B. Aircraft were fitted with their own transmitters that provided much more information about an aircraft. This was known as secondary radar and transmitted information about the aircraft directly from a transponder housed within the avionics (becoming a legal requirement by 1960). This paved new opportunities within the civil aviation realm which were rapidly growing from 1946 onwards.

Civilian Purposes

In 1946 the Civil Aeronautics Association (CAA) unveiled the first radar-equipped control tower for civil flights which heralded the beginning of Air Traffic Control as we know it today. By the early 1950’s the CAA were using radar full time as part of monitoring civil aviation.

Additionally to aviation based applications radar became useful for weather monitoring. During the Second World War, much interference on the scopes was identified as rainfall or other types of precipitation. Between 1960 and 1980 weather radar was continuously improved. By 2000 there were large, well-networked weather radar installations across America, Europe and Japan. This quickly spread across other developed countries and, in theory at least, means we should all get accurate weather forecasts!