Radar (radio detection and ranging)

Radar (radio detection and ranging)
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Name	Radar
Invented	1930s
Inventor	Several, including Robert Watson-Watt
Type	Sensor

Radar (radio detection and ranging) is an electronic sensing technology that uses radio waves to determine the range, angle, and velocity of objects. Developed in the early 20th century, radar matured through contributions from innovators and institutions across the United Kingdom, United States, Germany, and Japan, and has since become integral to aviation, maritime navigation, meteorology, and defense. Radar systems combine transmitter, antenna, receiver, and processor subsystems to detect targets from aircraft to precipitation.

History

Radar development involved multiple inventors and programs during the interwar and World War II eras, with early demonstrations by the teams around Heinrich Hertz, Christian Hülsmeyer, and researchers influenced by Guglielmo Marconi. Key wartime projects included British initiatives led by figures associated with Robert Watson-Watt and establishments such as Bawdsey Manor, while parallel efforts occurred at MIT Radiation Laboratory, Telefunken, and the Kawasaki Aircraft Company. Postwar advances were driven by institutions like Bell Labs, RAND Corporation, and national programs in the Soviet Union, France, and China, producing developments in pulse-Doppler techniques, phased arrays, and spaceborne sensors employed by agencies such as NASA and organizations including NATO.

Principles and Operation

Radar operates by transmitting radio frequency energy from an antenna and analyzing echoes returned from targets; this basic principle traces to discoveries by James Clerk Maxwell and experimental confirmations by Heinrich Hertz. Range measurement uses time-of-flight calculations linked to the speed of light, a constant studied in experiments by Albert A. Michelson and utilized in timing electronics developed in laboratories like Bell Labs. Directionality relies on antenna theory advanced by contributors such as Karl Jansky and Guglielmo Marconi successors, while velocity measurement exploits the Doppler effect first described by Christian Doppler and applied in systems influenced by research at MIT Radiation Laboratory.

Types and Applications

Radar encompasses many classes including pulse, continuous-wave, pulse-Doppler, monopulse, synthetic aperture radar, inverse synthetic aperture radar, and phased array systems developed at places like Lincoln Laboratory and Grumman. Civilian applications include air traffic control conducted by agencies such as Federal Aviation Administration, weather surveillance by services like the National Weather Service, maritime navigation guided by institutions including the International Maritime Organization, and spaceborne Earth observation by European Space Agency and NASA missions. Military applications span air defense networks exemplified by programs involving NORAD and carrier-based systems fielded by United States Navy and other services, as well as targeting and fire-control suites used by systems from manufacturers like Raytheon and BAE Systems.

Components and Design

A radar comprises transmitters, receivers, antennas, duplexers, signal processors, and power supplies, with design influences from laboratories such as Bell Labs and industrial firms including Siemens and Thales Group. Transmitters may be tube-based (klystron, magnetron) researched at General Electric and RCA or solid-state devices advanced by groups at Texas Instruments and Analog Devices. Antenna types include parabolic reflectors, planar phased arrays developed at Raytheon and Northrop Grumman, and conformal arrays used by OEMs like Lockheed Martin. Duplexers and circulators employ ferrite materials whose properties were investigated at institutions such as MIT and Fraunhofer Society.

Signal Processing and Detection

Radar signal processing applies techniques like matched filtering, pulse compression, clutter suppression, and moving target indication; mathematical foundations draw from work by Norbert Wiener and Claude Shannon, with practical algorithms refined at MIT Lincoln Laboratory and Bell Labs. Detection theory leverages statistical approaches developed by researchers at Harvard University and Princeton University and implemented in software and hardware from firms including IBM and Hewlett-Packard. Imaging modes such as synthetic aperture radar exploit platform motion in studies conducted by JPL and European Space Agency, while adaptive beamforming traces to research at University of Illinois and Stanford University.

Performance Metrics and Limitations

Radar performance is quantified by metrics including range resolution, angular resolution, minimum detectable signal, signal-to-noise ratio, probability of detection, and false alarm rate; seminal treatments appear in texts from IEEE and standards produced by International Telecommunication Union. Limitations stem from propagation phenomena studied by meteorologists at National Oceanic and Atmospheric Administration, from electronic countermeasures explored by defense laboratories in Admiralty Research Establishment and counter-countermeasure research at DARPA, and from regulatory frequency allocations administered by Federal Communications Commission and International Telecommunication Union.

Military and Civilian Use Cases

Military use cases include air and maritime surveillance in theaters associated with operations like those planned by NATO commands and carrier strike groups centered on vessels such as USS Nimitz, coastal defense systems fielded by nations including United Kingdom and Russia, and ballistic missile early warning networks akin to programs run by NORAD and U.S. Space Force. Civilian use cases include airport surveillance radar operated at hubs like Heathrow Airport and Hartsfield–Jackson Atlanta International Airport, weather radar networks such as NEXRAD maintained by National Weather Service, collision avoidance systems in civil aviation regulated by International Civil Aviation Organization, and remote sensing missions like ERS and Sentinel satellites run by European Space Agency.

Category:Electromagnetic radiation technologies