How radar was invented: Milestones, discoveries and revolutionary technology

Chain Home: AMES Type 1 CH East Coast radar installation at Poling, Sussex (Credit: United Kingdom Government/Royal Air Force)

2024 marks the the 80th anniversary of the D-Day landings, the largest seaborne invasion in history and the allied forces entrances into the Second World War.

In the latest issue of How It Works magazine we take a look closer look at one of the most influential pieces of technology that helped to win the war… radar.

One of the most pivotal moments in radar’s history was the creation of an early warning system in Great Britain, known under the codename ‘Chain Home’.

With word that the German military might bring ‘death-ray’ radio technology aboard their fighter planes to a second world war, Britain quickly constructed coastal radar stations to spot aircraft before they crossed its shores. Chain Home was a network of transmitter antennae and receiver stations for a giant radar system that could detect incoming aircraft from around 100 miles away. The transmitter antennae sent long pulses out into the English Channel to bounce off any incoming enemy aircraft and return to the receiver station. The encounter would then appear on a radar display, alerting the operator to the presence of the aircraft. This helped give the Royal Air Force enough time – around 20 minutes – to jump into fighter planes and face the enemy before they had the chance to reach land. By 1939 Britain had 18 Chain Home radar stations, and by the end of World War II, 53 had been constructed.

Chain Home also inspired the creation of new radar devices with greater ranges, including the cavity magnetron, a pioneering piece of technology that uses microwaves to spot fighter aircraft and military sea vessels.

Murray Niman, the senior radar and antennae engineer at BAE Systems reveals the impact that early radar had, not only on winning World War II but advancing science

Q: How precisely could Chain Home radar locate moving aircrafts?

A: A typical CH (Chain Home) site covered several acres and consisted of a transmitter site with three or four steel 360’ towers and a receiver site with four 240’ towers – the towers supported the antenna systems. The transmitter array floodlit the area in front of it and the receiver used radio direction finding techniques to locate the target position and height. Initially it could establish bearings quite accurately and ranges to within five miles, although this improved with time. Assessments of the large waves of aircraft also relied on some very experienced operators distinguishing the complex echoes to estimate aircraft numbers.  Later in the war, combinations of stations were able to track V2 rockets.

Q: What were the biggest advantages of Chain Home radar to Britain’s air defence?

A: During the battle of Britain, CH allowed us to get our limited number of fighter aircraft in the right place at the right time, while minimising fuel usage that long patrols would have needed. So overall, it acted as a key ‘force multiplier’. It is now recognised by historians that CH played an important part in winning the Battle of Britain. Its biggest advantage arose from a combination of the long-range radar data and the integrated manner as to how this information was used. It was sent by a high-quality general post office telephone system to filter rooms and then onto sector control rooms who scrambled our defending aircraft and told them where the target was. The Germans had no idea how we managed, time after time, to get our fighters flying out of the sun and attacking their bomber streams.

Q: What were the limitations of Chain Home radar?

A: One of the biggest was the fact that CH could only direct a fighter to within one mile – at best – of a target. In clear daylight conditions, this was acceptable but at night time or bad weather it was not. The size of the original CH system meant that integration onto an aircraft platform was impossible. However, this was recognised early on and development work on a suite of higher frequency VHF (very high frequency) radars for airborne and ground use started before CH was fully operational. Another problem was that the original CH coverage did not go right down to the ground, resulting in about 1,000 feet lower operational ceiling where targets could “fly under the radar”. This was eventually addressed by higher frequency developments ‘CH-Low’ and ‘CH-Extra-Low’. CH also could not see targets that were behind it, so once the bombers were over the UK coast they were almost invisible to CH.

Q: How did the invention of the cavity magnetron change the way that radar could be used, especially in combat? 

A: The long ‘metre’ wavelengths associated with early radars meant that they could not be miniaturised, such as for airborne use, and/or achieve greater resolution from compact antennae. The magnetron provided a powerful source of high frequency energy. This was instrumental to enabling radar equipment that could be made more compact, with higher range and bearing resolution. It led to microwave versions of Air to Surface Vessel (ASV) and Air Intercept radars that were installed in aircraft, as well as the landmark H2S ground scanning system. Microwave ASV radar could also detect surfaced U-boats and turned the Atlantic U-Boat war to our favour, restricting the U-Boat hunting grounds to a small strip of the Atlantic ocean between Great Britain and the USA. And a post-war spin-off of the magnetron development later led to their use in domestic microwave ovens!