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A modern high-gain UHF Yagi television antenna with 17 directors, and one reflector (made of four rods) shaped as a corner reflector Drawing of Yagi–Uda VHF television antenna from 1954, used for analog channels 2–4, 54–72 MHz (U.S. channels).
Drawing of a Yagi–Uda VHF television antenna used for analog channels 2–4, 54–72 MHz (U.S. channels). It has four parasitic elements: three directors (to left) and one reflector (to right) and one driven element which is a folded dipole (double rod) connected to a 300 Ω twin lead feedline down the mast to the television set.
Hidetsugu Yagi (八木 秀次, Yagi Hidetsugu, January 28, 1886 – January 19, 1976) was a Japanese electrical engineer from Osaka, Japan. When working at Tohoku Imperial University , he wrote several articles that introduced a new antenna designed by his assistant Shintaro Uda to the English-speaking world.
In its use as a television antenna, it was common to combine a log-periodic design for VHF with a Yagi for UHF, with both halves being roughly equal in size. This resulted in much higher gain for UHF, typically on the order of 10 to 14 dB on the Yagi side and 6.5 dB for the log-periodic. [5]
It is a two element Yagi-Uda antenna with folded dipole elements, and no director(s). Because of the folded ends, the element lengths are approximately 70% of the equivalent dipole length. The two-element design gives modest directivity (about 2.0 dB ) with a null towards the rear of the antenna, yielding a high front-to-back ratio : Gain up to ...
Outdoor antenna designs are often based on the Yagi–Uda antenna [16] or log-periodic dipole array (LPDA). [17] These are composed of multiple half-wave dipole elements, consisting of metal rods approximately half of the wavelength of the television signal, mounted in a line on a support boom.
The Yagi produces a fairly large gain (depending on the number of passive elements) and is widely used as a directional antenna with an antenna rotor to control the direction of its beam. It suffers from having a rather limited bandwidth, restricting its use to certain applications.
An endfire array of multiple dipole elements along a boom with gradually decreasing lengths, back to front, all connected to the transmission line with alternating polarity. It is a directional antenna with a wide bandwidth, which makes it ideal for use as a rooftop television antenna, although its gain is much less than a Yagi of comparable size.
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