Radar can spot an aircraft hundreds of kilometres away, track a storm’s rainfall, and guide a ship through fog — all without seeing anything. The technology works a lot like the echolocation bats use: it shouts into the darkness and listens for the echo. The difference is that radar shouts with radio waves, and it has been quietly underpinning aviation, weather forecasting, and defence for nearly a century.

What Radar Is and How the Name Came About

Radar is an acronym for “radio detection and ranging.” The term was coined by the US Navy in 1940 as a convenient label for a technology that uses radio waves — a form of electromagnetic radiation — to detect objects and measure their distance, direction, and speed.

Unlike cameras or the human eye, radar does not need light. Radio waves pass through darkness, fog, rain, and clouds, which is why radar became essential for aviation and naval operations long before modern sensors existed. The same principle powers everything from airport air-traffic control to the speed guns used by traffic police.

The Five Steps of a Radar Measurement

Every radar system, however advanced, runs the same basic cycle:

• Transmission: A transmitter generates a burst of high-frequency radio waves and sends them out through an antenna in a chosen direction.
• Propagation: The waves travel through the air at the speed of light — roughly 299,792 kilometres per second.
• Reflection: When the waves strike an object — an aircraft, a ship, a raindrop — some of the energy bounces back toward the source. This returning energy is the “echo.”
• Reception: The antenna, often the same one that transmitted, switches to receiving mode and captures the echo. A component called a duplexer handles the rapid switching between transmitting and receiving.
• Processing: The system measures the time between sending and receiving. Since the speed of radio waves is constant, half the round-trip time multiplied by the speed of light gives the object’s distance.

How Radar Measures Speed: The Doppler Effect

Distance is only half the story. Radar also measures how fast an object is moving, using the Doppler effect — the same phenomenon that makes an ambulance siren sound higher-pitched as it approaches and lower-pitched as it recedes.

If an object is moving toward the radar, the reflected waves return at a slightly higher frequency than the transmitted signal; if it is moving away, the frequency is slightly lower. By measuring this frequency shift, the radar calculates the object’s speed relative to the antenna, and whether it is closing in or moving off. Weather radars use the same principle to detect wind motion inside storms, which is how meteorologists spot the rotation that can signal a tornado.

The Main Types of Radar

Different jobs call for different radar designs:

• Pulse radar sends out short bursts of radio waves and listens for the return between pulses — the classic design, ideal for measuring range.
• Continuous-wave radar transmits constantly and uses Doppler shifts to detect motion; it is simpler and used in applications like speed guns and some proximity sensors.
• Doppler radar is optimised to measure the velocity of targets and is the backbone of modern weather forecasting.
• Phased-array radar uses many small antennas working together to steer the beam electronically, with no moving parts — allowing it to scan the sky almost instantly in multiple directions. These systems are widely used in military air defence and missile warning.
• Synthetic aperture radar (SAR) is mounted on aircraft and satellites and builds high-resolution images of landscapes and structures from the echoes collected as the platform moves — useful for mapping, surveillance, and disaster assessment.

A Short History: From Death Ray to Chain Home

Radar’s development accelerated in the 1930s as war loomed. In 1935, British radio physicist Robert Watson-Watt was asked to assess reports of a supposed German “death ray” based on radio. He and his assistant Arnold Wilkins quickly concluded such a weapon was impossible — but Wilkins suggested radio signals could instead be used to detect aircraft at long distance.

The idea was demonstrated in February 1935, when signals from a BBC short-wave transmitter were bounced off a Handley Page Heyford bomber. Watson-Watt then led the construction of a practical system, and by 1938 a network of fixed radar stations codenamed Chain Home was operational along Britain’s coasts. During the Battle of Britain in 1940, these stations gave the Royal Air Force vital advance warning of incoming German raids, letting fighters be scrambled to meet them — a decisive advantage that helped Britain win the battle.

Radar Today: Defence, Aviation, Weather, and Cars

In defence, radar remains the primary tool for air surveillance, air defence, and missile warning, with phased-array systems able to track many targets at once across vast areas. In civil aviation, air-traffic control radars keep aircraft safely separated, and onboard weather radars help pilots steer around storms.

Weather services operate radar networks that map rainfall and wind in real time; Australia alone runs more than 60 weather radars, one of the largest networks in the world. At sea, ship radars provide navigation and collision avoidance in poor visibility. And on the road, compact radar sensors — working alongside cameras — power adaptive cruise control and automatic emergency braking in modern cars. The same echo that once warned of bombers now stops a car before it hits a pedestrian.

FAQs

Can radar see through clouds and fog?
Yes. Radio waves pass through clouds, fog, rain, and darkness far better than visible light, which is exactly why radar is used for aviation, shipping, and weather monitoring in all conditions.

How far can radar detect objects?
It depends on the system’s power, frequency, and antenna size, as well as the target’s size and altitude. Long-range surveillance radars can reach hundreds of kilometres, while a car’s parking sensor works over a few metres. Range is always a trade-off with resolution and cost.

What is the difference between radar and lidar?
Both measure distance with echoes, but radar uses radio waves while lidar uses laser light. Lidar gives finer detail at short range but is blocked by fog and rain; radar reaches farther and works in bad weather.

Why do some aircraft claim to be “stealthy” against radar?
Stealth designs shape the aircraft and use special materials to reflect as little radio energy back toward the radar as possible, shrinking the echo. It does not make them invisible — it makes them detectable only at much shorter ranges.

Is radar harmful to people nearby?
Radar systems are designed and regulated to operate at safe exposure levels for the public, with high-power transmitters kept at distance from people or pointed away from populated areas. Everyday devices like car radar sensors operate at very low power.

Compiled by the Khabar 24h Editorial Desk from publicly available sources.