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Also called a beam antenna [4] and parasitic array, the Yagi is widely used as a directional antenna on the HF, VHF and UHF bands. [ 3 ] [ 4 ] It has moderate to high gain of up to 20 dBi , [ 3 ] depending on the number of elements used, and a front-to-back ratio of up to 20 dB.
However, a Yagi with the same number of elements as a log-periodic would have far higher gain, as all of those elements are improving the gain of a single driven element. 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.
The X-shaped dipoles give it a wide bandwidth to cover both the VHF (174–216 MHz) and UHF (470–700 MHz) bands. It has a gain of 5 dB VHF and 12 dB UHF and an 18 dB front-to-back ratio. The example shown is horizontally polarised. Reflective array 'billboard' antenna of the SCR-270 radar, an early US Army radar system. It consists of 32 ...
A directive antenna with moderate gain of about 8 dBi often used at UHF frequencies. Consists of a dipole mounted in front of two reflective metal screens joined at an angle, usually 90°. Used as a rooftop UHF television antenna and for point-to-point data links. Parabolic The most widely used high gain antenna at microwave frequencies and above.
The X-shaped dipoles give it a wide bandwidth to cover both the VHF (174–216 MHz) and UHF (470–700 MHz) TV bands. It has a gain of 5 dB VHF and 12 dB UHF and an 18 dB front-to-back ratio. Large planar array antenna of a VHF Russian mobile air defense radar, the Nebo-M. It consists of 175 folded dipole antennas.
It is difficult to design a single antenna to receive such a wide wavelength range, and there is an octave gap from 216 to 470 MHz between the VHF and UHF frequencies. So traditionally, separate antennas (outdoor antennas with separate sets of elements on a single support boom) have been used to receive the VHF and UHF channels. [6]
The driven elements between the UHF and VHF are then coupled and often matched for a 75 Ω coaxial downlead to the receiver. When a "driven element" is referred to in an antenna array, it is often assumed that other elements are not driven (i.e. passive radiator) and that the array is tightly coupled (spacing far below a wavelength).
Corner reflector UHF TV antenna from 1954 with bowtie dipole driven element. A corner reflector antenna is a type of directional antenna used at VHF and UHF frequencies. [1] [2] It was invented by John D. Kraus in 1938. [3] [4] It consists of a dipole driven element mounted in front of two flat rectangular reflecting screens joined at an angle ...
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