The History of RADAR

Podcast Transcript

In 1887, the German physicist Heinrich Hertz discovered radio waves.

While the first practical use of this discovery was communication, there were also some who realized that radio waves could serve another purpose.

It was possible to use these radio waves to detect objects at a distance. It was something that revolutionized warfare and weather forecasting and might revolutionize consumer technology.

Learn more about RADAR, how it works, and how it was developed on this episode of Everything Everywhere Daily.

The story of RADAR starts with the discovery of radio waves.

In 1864 the Scottish physicist James Clerk Maxwell developed a series of equations that predicted there existed electromagnetic waves, and that light was an example of such a wave.

The problem was no one could find proof of anything beyond visible light.

This was eventually solved by the German physicist Heinrich Hertz in 1887 discovered longer wavelengths of electromagnetic waves than light.

In the process of doing his research, he discovered something else. Certain wavelengths of radio waves were reflected by metal.

The initial use case for radio waves was for communications. Guglielmo Marconi developed a workable radio transmitter and receiver just seven years after Hertz’s discovery.

However, Hertz’s observation that some radio waves were reflected by metal still lingered.

The first person who attempted to take advantage of this effect was the German inventor Christian Hülsmeyer.

Hülsmeyer believed that this property of radio waves could be used to detect ships at sea to prevent collisions. He received a patent for a device called a Telemobiloscope which could detect ships in the fog.

The system threw out a very wide signal and had a very narrowly focused receiver with a parabolic antenna that could rotate a full 360 degrees.

This first attempt at using radio waves for detecting objects had many of the features of RADAR systems that are used today.

One of the biggest problems with using radio waves for detection has to do with the inverse square law.

The inverse square law indicates that generally speaking, the intensity of an electromagnetic wave is one over the square of the distance. Double the distance and a signal is only one-fourth as strong. Triple the distance, and it is one-ninth as strong.

In the case of using radio waves for detection, for any object that radio waves bounce off of, only a small fraction of the energy from the radio transmitter will hit it.

It then gets worse. As the radio wave is bounced back to the receiver, it is subject to the inverse square law again. So, the signal which is returned can be very, very weak, even if the signal is focused.

This is why Hülsmeyer’s Telemobiloscope had a parabolic antenna. A parabolic dish, which you’ve seen on any satellite dish, reflects all of the radio waves across the surface area of the dish to a single point. It amplifies the weak signal.

The Telemobiloscope would sweep around, and when it detected a radio wave being bounced back, it would ring an electric bell to indicate the direction of the object.

The device was given a public demonstration in May 1904 in Germany and then in June in the Netherlands at a conference of shipping executives. The demonstrations were done behind a curtain to show that it works without direct line of sight.

The newspapers reported on the event positively. One Dutch newspaper, De Telegraf, made the following prophetic observation “Because, above and underwater metal objects reflect waves, this invention might have significance for future warfare.”

The Telemobiloscope was tested on the Rhine River, but it never saw widespread adoption.

For several decades, radio detection technology languished. No one really did anything with it.

Researchers in multiple countries experimented with radio detection, and several prototypes were built.

The truth was, there wasn’t much of a need for it. Avoiding ship collisions was nice, but it really wasn’t that big of a problem.

The need for radio detection finally arose in the 1930s.

During the First World War, the Germans sent zeppelins over Britain on bombing missions. Despite being slow-moving and not doing much damage, the British were unable to intercept them because of the delay in detecting and scrambling aircraft.

As aircraft technology improved rapidly after the war, the need for some sort of aircraft detection system became necessary.

In 1934, a team at the US Naval Research Laboratory developed a pulsed radio detection system. It was able to detect an airplane over the Potomac River at a range of one mile. It was crude, but it proved the concept, and it was considered the first RADAR system.

Albert Taylor, Leo Young, and Robert Page are credited as being the inventors of RADAR.

In 1939, the US Navy began using the term RADAR as an acronym for “RAdio Detection And Ranging.”

A ship-based RADAR system was installed on the USS California, a battleship that was sunk at Pearl Harbor.

In Britain, one of the researchers who picked up the challenge was the British scientist Robert Watson-Watt.

Watson-Watt had previously worked on the detection of distant thunderstorms using radio. In the 1920s, he developed a system called high-frequency direction finding or HFDF, also known as “huff-duff.”

Huff-duff was used in the detection of u-boats extensively during WWII.

Watson-Watt figured this technology could be used to detect aircraft. On February 26, 1935, he and the Royal Air Force conducted the Daventry Experiment.

The Daventry Experiment used a shortwave transmitter owned by the BBC and a radio receiver to detect a bomber that was flying around at a distance of eight miles.

The experiment was considered a success and, in 1938, led to the creation of a system of radio location stations located on the coast of England known as the Chain Home system. The Chain Home system could detect German aircraft 99 miles or 160 kilometers away.

The Chain Home system proved invaluable in the Battle of Britain in 1940. The British were able to detect incoming German planes and could scramble to intercept them while they were still over France. Without the Chain Holm system, it is likely the Germans would have won the Battle of Britain.

The US and the UK didn’t share their RADAR technology in the run-up to the war. It wasn’t until the war started that there was a wider exchange of technology.

The US and the UK weren’t the only countries working on RADAR technology during the war. The Germans, Japanese, Soviets, and Italians were all developing their own systems.

During the war, there were significant advancements in RADAR technology, including the American invention of the duplexer, which allowed for a transmitter and receiver to put in the same device, and the British invention of the cavity magnetron, which allowed for smaller, more portable systems.

A cavity magnetron is very similar to the device inside modern microwave ovens.

RADAR had proven its importance during World War II. After the war, the development of RADAR technology continued unabated and became even more important.

During the Cold War, RADAR became the first line of defense. The Americans and Canadians developed a series of lines of RADAR stations that extended from the Aleutian Islands across Canada, Greenland, and the Faroe Islands.

The first was the Pinetree Line which ran near the US-Canadian Border. The second was the Mid-Canada Line, and the furthest was the Distant Early Warning line.

All of the RADAR data was sent to a central Strategic Air Command, which could send planes to intercept bombers.

One of the discoveries during World War II was that RADAR could detect precipitation. This discovery led to the use of RADAR in weather forecasting.

The first famous use of RADAR for weather forecasting was in 1961 when a young local Texas reporter by the name of Dan Rather went to a weather radar facility in Galveston, Texas, to cover Hurricane Carla.

He got permission to broadcast live from the site and got the managers of the facility to draw a rough outline of the Gulf of Mexico on a transparent sheet of plastic. He then held the sheet over the radar display to show viewers the size and location of the storm.

Thanks to his efforts in displaying the scope of the storm to viewers, hundreds of thousands fled, and there were only 35 deaths, compared to the 12,000 deaths from a similar hurricane in 1900.

RADAR also became a staple of air traffic control systems around the world. It was used to track commercial aircraft so air traffic controllers could avoid collisions and control all the planes taking off and landing at commercial airports.

RADAR systems shrunk and were put inside individual aircraft, which became important for military fighters. RADARs could detect enemy aircraft, and RADAR was used in surface-to-air and air-to-air missiles

As with all weapon systems in history, countermeasures are soon developed to thwart them. In the case of RADAR, there were several technologies developed to thwart it.

Chaff was developed in World War II to confuse RADAR. Chaff is nothing more than small particles of metal, usually aluminum, which is designed to amplify a reflected RADAR signal.

RADAR jamming is nothing more than sending out a radio signal on the same wavelength in an attempt to overwhelm a RADAR receiver so it can’t pick up the reflected radio signal.

Perhaps the most interesting RADAR countermeasure is stealth technology. Stealth is a collection of different methods to make planes or ships invisible to RADAR.

There are two primary ways this can be done. The first is to deflect the radio waves away such that they aren’t reflected back to the receiver.

The second is to coat a vehicle in a substance that will absorb radio waves such that very little is reflected back.

Aircraft such as the B2 bomber, the F-117A Nighthawk, and the F-22 Raptor have both characteristic sharp angles and absorbent coatings.

The F-117A Nighthawk was primarily used in the Iraq War to take out RADAR and antiaircraft installations, which would then allow non-stealth aircraft to fly safely.

RADAR has advanced to the point where the technology is now starting to appear in everyday life. Entire RADAR systems can now be integrated on a single chip which can be deployed in a wide variety of applications.

Automobiles are now being equipped with low-power RADAR to help with accident avoidance.

Rear bicycle lights now come with RADAR which will provide an audible alert for riders if a car is in proximity.

RADAR has been integrated into some smart lights which can monitor sleeping activity and breathing. They can also detect if someone has fallen down and call for help.

Robots in factories and warehouses are equipped with RADAR to avoid obstacles and to sense nearby objects.

Many consumer drones use low-power RADAR to avoid objects and to measure their distance from the ground.

There are also plans to implement RADAR into computer monitors, which could detect gestures for playing games or reading sign language. This technology is also being considered for automobiles for people to control an automotive display without having to touch anything.

Geologists point RADAR at the ground to detect objects below the surface, and astronomers use RADAR to track meteors and other nearby objects in space.

RADAR has come a long way from the crude systems used to detect ships in the fog over 100 years ago. It has gone from the military to weather forecasting to our homes and automobiles.

Given the advances in millimeter wavelength RADAR and RADAR systems on a chip, we can expect even more uses for RADAR technology in our everyday lives over the next several decades.

The Executive Producer of Everything Everywhere Daily is Charles Daniel.

The associate producers are Thor Thomsen and Peter Bennett.

I have two reviews for you today. The first review is a three-star review from listener MSheritage on Apple Podcasts in the United States. They write:

Good show

Good show, professional and full of knowledge. However, I have been disappointed with the topics of late. The show has not featured a interesting topic in weeks. Is a bit repetitive and has very little American history involved.

Thanks, MSheritage! Note to self, more American history.

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US centric

It’s US / North American centric, not everything everywhere. Speaking too quickly just to make it sound thrilling is pointless. It would be better if it were slower b

Thanks, BogW! Note to self, less American history.

I think my lesson for today is that it is literally impossible to please everyone.

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