Fișier:Wilmer Barrow & horn antenna 1938.jpg

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DescriereWilmer Barrow & horn antenna 1938.jpg	English: The first modern horn antenna and its inventor, Wilmer L. Barrow in 1938. A horn antenna is a flaring metal horn used to direct microwaves from a waveguide into a beam. Although Jagadish Chandra Bose invented the horn antenna during his pioneering 1897 experiments with microwaves, subsequent development of radio used much lower frequencies at which horns were unsuitable, and the concept of a horn to direct radio waves was forgotten. Around 1933 Barrow at Massachusetts Institute of Technology reinvented the horn antenna during research into microwave detection of aircraft, and published his work in 1938. Caption: "Metal horn recently devised and successfully used by Prof. Wilmer L. Barrow in focusing ultra-short waves; waves in the range 300 to 4300 megacycles (wavelengths from 1 meter to 7 centimeters)."
Dată	octombrie 1938
Sursă	Retrieved October 27, 2015 from "Metal Horn Focuses Ultra-Short Waves" in Short Wave Craft magazine, Popular Book Corp., Springfield, MA, USA, Vol. 9, No. 6, October 1938, p. 332 on http://www.americanradiohistory.com
Autor	NecunoscutUnknown author
Permisiune (Reutilizarea acestui fișier)	This 1938 issue of Short Wave Craft magazine would have the copyright renewed in 1966. Online page scans of the Catalog of Copyright Entries, published by the US Copyright Office can be found here. Search of the Renewals for Periodicals for 1965, 1966, and 1967 show no renewal entries for Short Wave Craft. Therefore the copyright was not renewed and it is in the public domain.

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This work is in the public domain because it was published in the United States between 1929 and 1963, and although there may or may not have been a copyright notice, the copyright was not renewed. For further explanation, see Commons:Hirtle chart and the copyright renewal logs. Note that it may still be copyrighted in jurisdictions that do not apply the rule of the shorter term for US works (depending on the date of the author's death), such as Canada (70 years p.m.a.), Mainland China (50 years p.m.a., not Hong Kong or Macao), Germany (70 years p.m.a.), Mexico (100 years p.m.a.), Switzerland (70 years p.m.a.), and other countries with individual treaties.

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