Radar

Lore & Background

Early experiments with radio wave reflection date to 1886, when Heinrich Hertz showed that radio waves could reflect from solid objects. In 1897, Alexander Popov noted interference from a passing vessel while testing ship-to-ship communication, suggesting the phenomenon might detect objects. Christian Hülsmeyer in 1904 demonstrated detection of a ship in fog and obtained patents for a full radar system he called a telemobiloscope, using a 50 cm wavelength and spark-gap transmitter, but German military officials rejected it.

In 1922, U.S. Navy researchers A. Hoyt Taylor and Leo C. Young observed that ships passing between a transmitter and receiver caused fading signals, and in 1930 Lawrence A. Hyland noted similar effects from aircraft, leading to further research at the Naval Research Laboratory. In the UK, L. S. Alder took out a secret provisional patent for naval radar in 1928, and W.A.S. Butement and P. E. Pollard built a successful breadboard test unit at 50 cm with pulsed modulation. In 1935, Robert Watson-Watt and Arnold Frederic Wilkins, prompted by reports of aircraft causing radio interference, conducted the Daventry Experiment using a BBC shortwave transmitter and a GPO receiver, detecting a bomber. This led to immediate funding and the patent GB593017.

Before World War II, radar research was conducted in the United Kingdom, the United States, France, Germany, Italy, Japan, the Soviet Union, and the Netherlands. The first pulsed radar system was demonstrated in December 1934 by Robert M. Page at the Naval Research Laboratory. The cavity magnetron, developed in the United Kingdom, allowed relatively small systems with sub-meter resolution.

Reader's Guide

Radar's significance lies in its diverse modern uses, including air and terrestrial traffic control, air-defense and anti-missile systems, marine navigation, aircraft anti-collision, ocean and outer space surveillance, meteorological precipitation monitoring, altimetry, flight control, guided missile target locating, self-driving cars, and ground-penetrating geological observation. Modern high-tech radar systems employ digital signal processing and machine learning to extract useful information from very high noise levels.

The technology was developed secretly for military use by several countries before and during World War II. Its legacy includes enabling automated platforms such as driverless vehicles to monitor their environment, preventing unwanted incidents. Other similar systems, like lidar, use different regions of the electromagnetic spectrum, but radar remains a foundational tool for detection and ranging across many domains.