Editing Radar (section)

=== 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>