Radar: From Aircraft Detection to Autonomous Driving

By Oliver Bean - Engineering Student @ Wadham College, Oxford

---

One technology that has been critical to digitalisation is wireless communication. Without it, we wouldn’t be able to access satellites and GPS - or even use our home WiFi. Wireless technologies utilise electromagnetic waves - these are invisible to the naked eye but ubiquitous in the modern world. Radar was the first major use of electromagnetic waves and ‘wireless’ technology; radar created the foundations for our entire modern communication systems.

During the Second World War, Britain pioneered development of a novel technology used to detect aerial enemy attacks. Named ‘RADAR’, an antenna was used to direct high power microwaves at oncoming aircraft. The microwaves travel at the speed of light through the air - and upon impact with the body of an aircraft some of the bursts of microwave reflect back towards the radar. These reflections can be detected and the time difference between the incoming and outgoing pulses allows calculation of the speed and distance of an object such as a plane. This was a milestone in wireless technology and saved countless lives during the war.

However, there were a number of engineering challenges that had to be overcome to produce a working radar and these problems persist today for wireless technologies. Firstly, radar signals required large amounts of energy to produce. The amount of energy required to send a radar pulse is dependent on distance - but raised to the power of four.

This can be explained by looking at the underlying physics and a rule named the’ inverse square law’ which applies to a point source - for example a source of light such as the sun or a source of electrical charge such as an electron. The law states that the intensity of the radiation is inversely proportional to the square of the distance from the source. Radar technology obeys exactly this law - the issue is that radar utilises both a microwave that is emitted and then the same wave reflected back - which compounds the effect. This explains why microwaves required large amounts of energy to generate. The ‘inverse square law’ is a commonly occurring phenomenon and applies to electricity, gravity and all electromagnetic waves. A device invented in 1940 - named the magnetron - solved the problem of generating high energy waves. By using the interaction of magnetic and electric fields to produce a resonant frequency of microwave, the magnetron was able to create high power and compact radar units.

Secondly, another issue is that waves are susceptible to interference from particles in the air, particularly in rainy or snowy conditions. This effect can be minimised by using waves that have longer wavelengths. Microwaves were chosen for radar applications because they have an ideal wavelength that both reduces this attenuation and minimises power use.

Radar was one of the first practical uses of electromagnetic waves in an engineering application. Radar has since paved the way for the development of FM radio, AM radio and modern WiFi - these types of wireless communication have been critical to digitalisation.

However, is a common conception that radar itself is an outdated technology. Whilst the technology has not radically changed since its conception, the future applications of radar are wide ranging. Even today, radar is a vital component of car cruise control systems and will be central to developing autonomous cars. Imaging radar can be used in medical settings and in airport security and researchers are even using radar to investigate sea ice thickness in the Arctic Circle.

Further reading:

1. How a Magnetron Works: https://www.youtube.com/watch?v=bUsS5KUMLvw

2. The Inverse Square Law: http://hyperphysics.phy-astr.gsu.edu/hbase/Forces/isq.html

3. The Radar Equation: https://www.radartutorial.eu/01.basics/The%20Radar%20Range%20Equation.en.html