Editing Radar (section)

== History ==
{{Main|History of radar}}

=== First experiments ===
As early as 1886, German physicist [[Heinrich Hertz]] showed that radio waves could be reflected from solid objects. In 1895, [[Alexander Stepanovich Popov|Alexander Popov]], a physics instructor at the [[Imperial Russian Navy]] school in [[Kronstadt]], developed an apparatus using a [[coherer]] tube for detecting distant lightning strikes. The next year, he added a [[spark-gap transmitter]]. In 1897, while testing this equipment for communicating between two ships in the [[Baltic Sea]], he took note of an [[interference beat]] caused by the passage of a third vessel. In his report, Popov wrote that this phenomenon might be used for detecting objects, but he did nothing more with this observation.<ref>Kostenko, A.A., A.I. Nosich, and I.A. Tishchenko, "Radar Prehistory, Soviet Side," ''Proc. of IEEE APS International Symposium 2001,'' vol. 4. p. 44, 2003</ref>

The German inventor [[Christian Hülsmeyer]] was the first to use radio waves to detect "the presence of distant metallic objects". In 1904, he demonstrated the feasibility of detecting a ship in dense fog, but not its distance from the transmitter.<ref name="radarworld.org">{{cite web|url=http://www.radarworld.org/huelsmeyer.html|title=Christian Huelsmeyer, the inventor|work=radarworld.org|access-date=18 February 2007|archive-date=27 December 2017|archive-url=https://web.archive.org/web/20171227233002/http://www.radarworld.org/huelsmeyer.html|url-status=live}}</ref> He obtained a patent<ref>[//upload.wikimedia.org/wikipedia/commons/1/11/DE165546.pdf ''Patent DE165546; Verfahren, um metallische Gegenstände mittels elektrischer Wellen einem Beobachter zu melden.'']</ref> for his detection device in April 1904 and later a patent<ref>[//upload.wikimedia.org/wikipedia/commons/e/e9/DE169154.pdf ''Verfahren zur Bestimmung der Entfernung von metallischen Gegenständen (Schiffen o. dgl.), deren Gegenwart durch das Verfahren nach Patent 16556 festgestellt wird.'']</ref> for a related amendment for estimating the distance to the ship. He also obtained a British patent on 23 September 1904<ref>{{patent|GB|13170|''Telemobiloscope''}} {{Dead link|date=June 2020}}</ref> for a full radar system, that he called a ''telemobiloscope''. It operated on a 50&nbsp;cm wavelength and the pulsed radar signal was created via a spark-gap. His system already used the classic antenna setup of horn antenna with parabolic reflector and was presented to German military officials in practical tests in [[Cologne]] and [[Rotterdam]] harbour but was rejected.<ref>{{cite web |url=http://100-jahre-radar.fraunhofer.de/img/gdr_zeichnungpatent.jpg |title=gdr_zeichnungpatent.jpg |access-date=24 February 2015 |archive-date=24 February 2015 |archive-url=https://web.archive.org/web/20150224135053/http://100-jahre-radar.fraunhofer.de/img/gdr_zeichnungpatent.jpg |url-status=dead }}</ref>

In 1915, [[Robert Watson-Watt]] used radio technology to provide advance warning of thunderstorms to airmen<ref>{{cite news|title=Making waves: Robert Watson-Watt, the pioneer of radar|url=https://www.bbc.co.uk/news/uk-scotland-tayside-central-27393558|publisher=BBC|date=16 February 2017|access-date=20 July 2018|archive-date=28 February 2017|archive-url=https://web.archive.org/web/20170228025758/http://www.bbc.co.uk/news/uk-scotland-tayside-central-27393558|url-status=live}}</ref><ref>{{cite web |title=Robert Wattson-Watt |url=https://lemelson.mit.edu/resources/robert-wattson-watt |website=The Lemelson-MIT Program |access-date=1 December 2023}}</ref> and during the 1920s went on to lead the U.K. research establishment to make many advances using radio techniques, including the probing of the [[ionosphere]] and the detection of [[lightning]] at long distances. Through his lightning experiments, Watson-Watt became an expert on the use of [[radio direction finding]] before turning his inquiry to [[shortwave]] transmission. Requiring a suitable receiver for such studies, he told the "new boy" [[Arnold Frederic Wilkins]] to conduct an extensive review of available shortwave units. Wilkins would select a [[General Post Office]] model after noting its manual's description of a "fading" effect (the common term for interference at the time) when aircraft flew overhead.

By placing a transmitter and receiver on opposite sides of the [[Potomac River]] in 1922, U.S. Navy researchers [[A. Hoyt Taylor]] and [[Leo C. Young]] discovered that ships passing through the beam path caused the received signal to fade in and out. Taylor submitted a report, suggesting that this phenomenon might be used to detect the presence of ships in low visibility, but the Navy did not immediately continue the work. Eight years later, [[Lawrence A. Hyland]] at the [[Naval Research Laboratory]] (NRL) observed similar fading effects from passing aircraft; this revelation led to a patent application<ref>Hyland, L.A, A.H. Taylor, and L.C. Young; "System for detecting objects by radio," U.S. Patent No. 1981884, granted 27 November 1934</ref> as well as a proposal for further intensive research on radio-echo signals from moving targets to take place at NRL, where Taylor and Young were based at the time.<ref>{{cite book|last=Howeth|first=Linwood S.|chapter=Ch. XXXVIII Radar|title=History of Communications-Electronics in the United States Navy|date=1963|publisher=Washington|chapter-url=https://babel.hathitrust.org/cgi/pt?id=uiug.30112064674325;view=1up;seq=475}}</ref>

Similarly, in the UK, L. S. Alder took out a secret provisional patent for Naval radar in 1928.<ref>{{cite book |last1=Coales |first1=J.F. |title=The Origins and Development of Radar in the Royal Navy, 1935–45 with Particular Reference to Decimetric Gunnery Equipments |date=1995 |publisher=Springer |isbn=978-1-349-13457-1 |pages=5–66}}</ref> [[W. A. S. Butement|W.A.S. Butement]] and P. E. Pollard developed a [[breadboard]] test unit, operating at 50&nbsp;cm (600&nbsp;MHz) and using pulsed modulation which gave successful laboratory results. In January 1931, a writeup on the apparatus was entered in the ''Inventions Book'' maintained by the Royal Engineers. This is the first official record in Great Britain of the technology that was used in coastal defence and was incorporated into [[Chain Home]] as [[Chain Home Low|Chain Home (low)]].<ref>Butement, W. A. S., and P. E. Pollard; "Coastal Defence Apparatus", ''Inventions Book of the Royal Engineers Board'', Jan. 1931</ref><ref>Swords, S. S.; ''tech. History of the Beginnings of Radar'', Peter Peregrinus, Ltd, 1986, pp. 71–74</ref>

===Before World War II===
[[File:Early radar antenna - US Naval Research Laboratory Anacostia.jpg|thumb|upright=0.8|Experimental radar antenna, US [[Naval Research Laboratory]], Anacostia, D. C., from the late 1930s (photo taken in 1945)]]
Before the [[Second World War]], researchers in the United Kingdom, [[French Third Republic|France]], [[Nazi Germany|Germany]], [[Kingdom of Italy|Italy]], [[Japanese Empire|Japan]], the [[Netherlands]],<ref>{{cite web|url=https://www.museumwaalsdorp.nl/en/museum-waalsdorp-2/airacous/air-acoustics-electric-listening-device/ |title=The "Electric listening device" (1936 – 1941) |website=museumwaalsdorp.nl |access-date=2024-11-10}}</ref> the [[Soviet Union]], and the United States, independently and in great secrecy, developed technologies that led to the modern version of radar. Australia, Canada, New Zealand, and South Africa followed prewar Great Britain's radar development, [[Regency of Hungary|Hungary]] and Sweden generated its radar technology during the war.{{citation needed|date=September 2024}}

In France in 1934, following systematic studies on the [[Cavity Magnetron#Split-anode magnetron|split-anode magnetron]], the research branch of the [[Compagnie générale de la télégraphie sans fil]] (CSF) headed by Maurice Ponte with Henri Gutton, Sylvain Berline and M. Hugon, began developing an obstacle-locating radio apparatus, aspects of which were installed on the ocean liner [[SS Normandie|''Normandie'']] in 1935.<ref>{{cite magazine|title= Radio Waves Warn Liner of Obstacles in Path|magazine= Popular Mechanics|url= https://books.google.com/books?id=x98DAAAAMBAJ&pg=PA844|date= December 1935|publisher= Hearst Magazines|page= 844|access-date= 11 February 2021|archive-date= 7 October 2024|archive-url= https://web.archive.org/web/20241007062109/https://books.google.com/books?id=x98DAAAAMBAJ&pg=PA844#v=onepage&q&f=false|url-status= live}}</ref><ref>Frederick Seitz, Norman G. Einspruch, Electronic Genie: The Tangled History of Silicon  – 1998 – page 104</ref>

During the same period, Soviet military engineer [[Pavel K. Oshchepkov|P.K. Oshchepkov]], in collaboration with the [[Saint Petersburg State Electrotechnical University|Leningrad Electrotechnical Institute]], produced an experimental apparatus, RAPID, capable of detecting an aircraft within 3&nbsp;km of a receiver.<ref>John Erickson. Radio-Location and the Air Defence Problem: The Design and Development of Soviet Radar. ''Science Studies'', vol. 2, no. 3 (Jul. 1972), pp. 241–263</ref> The Soviets produced their first mass production radars RUS-1 and RUS-2 Redut in 1939 but further development was slowed following the arrest of Oshchepkov and his subsequent [[gulag]] sentence. In total, only 607 Redut stations were produced during the war. The first Russian airborne radar, [[Gneiss-2]], entered into service in June 1943 on [[Petlyakov Pe-2|Pe-2]] dive bombers. More than 230 Gneiss-2 stations were produced by the end of 1944.<ref>{{cite web | url=http://kret.com/en/news/3657/ | title=The history of radar, from aircraft radio detectors to airborne radar | work=kret.com | date=17 February 2015 | access-date=28 April 2015 | url-status=dead | archive-url=https://web.archive.org/web/20150620161506/http://kret.com/en/news/3657/ | archive-date=20 June 2015 }}</ref> The French and Soviet systems, however, featured continuous-wave operation that did not provide the full performance ultimately synonymous with modern radar systems.

Full radar evolved as a pulsed system, and the first such elementary apparatus was demonstrated in December 1934 by the American [[Robert Morris Page|Robert M. Page]], working at the [[Naval Research Laboratory]].<ref>Page, Robert Morris, ''The Origin of Radar'', Doubleday Anchor, New York, 1962, p. 66</ref> The following year, the [[United States Army]] successfully tested a primitive surface-to-surface radar to aim [[Coastal artillery|coastal battery]] [[searchlight]]s at night.<ref>{{cite magazine|title= Mystery Ray Locates 'Enemy'|magazine= Popular Science|url= https://books.google.com/books?id=bygDAAAAMBAJ&pg=PA29|date= October 1935|publisher= Bonnier Corporation|page= 29|access-date= 11 February 2021|archive-date= 7 October 2024|archive-url= https://web.archive.org/web/20241007062141/https://books.google.com/books?id=bygDAAAAMBAJ&pg=PA29#v=onepage&q&f=false|url-status= live}}</ref> This design was followed by a pulsed system demonstrated in May 1935 by [[Rudolf Kühnhold]] and the firm {{ill|Gesellschaft für elektroakustische und mechanische Apparate|lt=GEMA|de|GEMA (Radar)}} in Germany and then another in June 1935 by an [[Air Ministry]] team led by [[Robert Watson-Watt]] in Great Britain.

[[File:Watson Radar.jpg|thumb|left|The first workable unit built by [[Robert Watson-Watt]] and his team]]
In 1935, Watson-Watt was asked to judge recent reports of a German radio-based [[death ray]] and turned the request over to Wilkins. Wilkins returned a set of calculations demonstrating the system was basically impossible. When Watson-Watt then asked what such a system might do, Wilkins recalled the earlier report about aircraft causing radio interference. This revelation led to the [[Daventry Experiment]] of 26 February 1935, using a powerful [[BBC]] shortwave transmitter as the source and their GPO receiver setup in a field while a bomber flew around the site. When the plane was clearly detected, [[Hugh Dowding]], the [[Air Member for Supply and Research]], was very impressed with their system's potential and funds were immediately provided for further operational development.<ref name="Alan Dower Blumlein-2002">{{cite web|url=http://www.doramusic.com/Radar.htm |title=The story of RADAR Development |author=Alan Dower Blumlein |year=2002 |access-date=6 May 2011 |url-status=dead |archive-url=https://web.archive.org/web/20110710144447/http://www.doramusic.com/Radar.htm |archive-date=10 July 2011 }}</ref> Watson-Watt's team patented the device in patent GB593017.<ref name="BREVET D'INVENTION-1934">{{cite web|language=fr|url=http://www.radar-france.fr/brevet%20radar1934.htm|title=Nouveau système de repérage d'obstacles et ses applications|trans-title=New obstacle detection system and its applications|url-status=dead|archive-url=https://web.archive.org/web/20090116093441/http://www.radar-france.fr/brevet%20radar1934.htm|archive-date=16 January 2009|work=BREVET D'INVENTION|date=20 July 1934|via=radar-france.fr}}</ref><ref>{{cite press release|url=http://www.patent.gov.uk/media/pressrelease/2001/1009.htm|title=British man first to patent radar|date=10 September 2001|website=Media Centre|publisher=The Patent Office|url-status=dead|archive-url=https://web.archive.org/web/20060719224405/http://www.patent.gov.uk/media/pressrelease/2001/1009.htm|archive-date=19 July 2006}}</ref><ref>{{patent|GB|593017|''Improvements in or relating to wireless systems''}}</ref>

[[File:Chain home.jpg|thumb|upright=0.65|A [[Chain Home]] tower in Great Baddow, Essex, United Kingdom]]
[[File:Watson watt 02 fr.jpg|thumb|left|Memorial plaque commemorating Robert Watson-Watt and [[Arnold Wilkins]]]]
Development of radar greatly expanded on 1 September 1936, when Watson-Watt became superintendent of a new establishment under the British [[Air Ministry]], Bawdsey Research Station located in [[Bawdsey Manor]], near Felixstowe, Suffolk. Work there resulted in the design and installation of aircraft detection and tracking stations called "[[Chain Home]]" along the East and South coasts of England in time for the outbreak of World War II in 1939. This system provided the vital advance information that helped the Royal Air Force win the [[Battle of Britain]]; without it, significant numbers of fighter aircraft, which Great Britain did not have available, would always have needed to be in the air to respond quickly. The radar formed part of the "[[Dowding system]]" for collecting reports of enemy aircraft and coordinating the response.

Given all required funding and development support, the team produced working radar systems in 1935 and began deployment. By 1936, the first five Chain Home (CH) systems were operational and by 1940 stretched across the entire UK including Northern Ireland. Even by standards of the era, CH was crude; instead of broadcasting and receiving from an aimed antenna, CH broadcast a signal floodlighting the entire area in front of it, and then used one of Watson-Watt's own radio direction finders to determine the direction of the returned echoes. This fact meant CH transmitters had to be much more powerful and have better antennas than competing systems but allowed its rapid introduction using existing technologies.

===During World War II===
{{main|Radar in World War II}}
[[File:East Coast Chain Home radar station CH15176.jpg|thumb|East Coast [[Chain Home]] radar operators in England]]
A key development was the [[cavity magnetron]] in the UK, which allowed the creation of relatively small systems with sub-meter resolution. Britain shared the technology with the U.S. during the 1940 [[Tizard Mission]].<ref name="Angela Hind-2007">{{cite news |url=http://news.bbc.co.uk/1/hi/sci/tech/6331897.stm |title=Briefcase 'that changed the world' |publisher=BBC News |author=Angela Hind |date=5 February 2007 |access-date=16 August 2007 |quote=It not only changed the course of the war by allowing us to develop airborne radar systems, it remains the key piece of technology that lies at the heart of your microwave oven today. The cavity magnetron's invention changed the world. |archive-date=15 November 2007 |archive-url=https://web.archive.org/web/20071115140606/http://news.bbc.co.uk/1/hi/sci/tech/6331897.stm |url-status=live }}</ref><ref>{{cite news|last1=Harford|first1=Tim|title=How the search for a 'death ray' led to radar|url=https://www.bbc.co.uk/news/business-41188464|access-date=9 October 2017|work=BBC World Service|date=9 October 2017|quote=But by 1940, it was the British who had made a spectacular breakthrough: the resonant cavity magnetron, a radar transmitter far more powerful than its predecessors.... The magnetron stunned the Americans. Their research was years off the pace.|archive-date=9 October 2017|archive-url=https://web.archive.org/web/20171009003404/http://www.bbc.co.uk/news/business-41188464|url-status=live}}</ref>

In April 1940, ''[[Popular Science]]'' showed an example of a radar unit using the Watson-Watt patent in an article on air defence.<ref>{{cite magazine|title= Night Watchmen of the Skies|magazine= Popular Science|url= https://books.google.com/books?id=hCcDAAAAMBAJ&pg=PA56|date= December 1941|publisher= Bonnier Corporation|page= 56|access-date= 11 February 2021|archive-date= 7 October 2024|archive-url= https://web.archive.org/web/20241007062141/https://books.google.com/books?id=hCcDAAAAMBAJ&pg=PA56#v=onepage&q&f=false|url-status= live}}</ref> Also, in late 1941 ''[[Popular Mechanics]]'' had an article in which a U.S. scientist speculated about the British early warning system on the English east coast and came close to what it was and how it worked.<ref name="Popular Mechanics-1941">{{cite magazine|title=Odd-shaped Boats Rescue British Engineers|magazine= Popular Mechanics|url= https://archive.org/details/bub_gb_mtkDAAAAMBAJ/page/n67|date= September 1941|publisher= Hearst Magazines|page= 26}}</ref> Watson-Watt was sent to the U.S. in 1941 to advise on air defense after Japan's [[attack on Pearl Harbor]].<ref>{{cite news|title=Scotland's little-known WWII hero who helped beat the Luftwaffe with invention of radar set to be immortalised in film|url=http://www.dailyrecord.co.uk/news/real-life/scotlands-little-known-wwii-hero-who-3882904|newspaper=Daily Record|date=16 February 2017|access-date=16 February 2017|archive-date=17 February 2017|archive-url=https://web.archive.org/web/20170217064126/http://www.dailyrecord.co.uk/news/real-life/scotlands-little-known-wwii-hero-who-3882904|url-status=live}}</ref> [[Alfred Lee Loomis]] organized the secret [[MIT Radiation Laboratory]] at [[Massachusetts Institute of Technology]], Cambridge, Massachusetts which developed microwave radar technology in the years 1941–45. Later, in 1943, Page greatly improved radar with the [[Monopulse radar|monopulse technique]] that was used for many years in most radar applications.<ref>{{cite web | last=Goebel | first=Greg | title=The Wizard War: WW2 & The Origins of Radar | url=https://vc.airvectors.net/ttwiz_01.html | date=1 January 2007 | access-date=24 March 2007 | archive-date=2024-07-12 | archive-url=https://web.archive.org/web/20240712174051/https://vc.airvectors.net/ttwiz_01.html | url-status=live}}</ref>

The war precipitated research to find better resolution, more portability, and more features for radar, including small, lightweight sets to equip [[night fighter]]s ([[aircraft interception radar]]) and [[maritime patrol aircraft]] ([[air-to-surface-vessel radar]]), and complementary navigation systems like [[Oboe (navigation)|Oboe]] used by the [[Pathfinder (RAF)|RAF's Pathfinder]].