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Yagi–Uda Antenna

, or simply Yagi antenna, is a directional antenna consisting of two or more parallel resonant antenna elements in an end-fire array;[1] these elements are most often metal rods acting as half-wave dipoles.[2] Yagi–Uda antennas consist of a single driven element connected to a radio transmitter or receiver (or both) through a transmission line, and additional passive radiators with no electrical connection, usually including one so-called reflector and any number of directors.[2][3][4] It was invented in 1926 by Shintaro Uda of Tohoku Imperial University, Japan,[5] with a lesser role played by his boss Hidetsugu Yagi.[5][6] Reflector elements (usually only one is used) are slightly longer than the driven dipole and placed behind the driven element, opposite the direction of intended transmission. Directors, on the other hand, are a little shorter and placed in front of the driven element in the intended direction.[4] These parasitic elements are typically off-tuned short-circuited dipole elements, that is, instead of a break at the feedpoint (like the driven element) a solid rod is used.

[4] For applications that require wider bandwidths, such as terrestrial television, Yagi–Uda antennas commonly feature trigonal reflectors, and larger diameter conductors, in order to cover the relevant portions of the VHF and UHF bands. Vertically polarized arrays can be seen on the cheeks of the P-61 and on the nose cones of many WWII aircraft, notably the Lichtenstein radar-equipped examples of the German Junkers Ju 88 R-1 fighter-bomber, and the British Bristol Beaufighter night-fighter and Short Sunderland flying-boat. Sendai, Japan: The Research Institute of Electrical Communication, Tohoku University.^ Yagi Antenna Design, Peter P. Viezbicke, National Bureau of Standard Technical Note 688, December 1976^ a b Brown, 1999, p. 138^ Graf, Rudolf F. (June 1959).

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