Active antenna
Encyclopedia
An active antenna is an antenna
that contains active electronic components. This allows the construction of antennas of limited size and / or wide frequency range. Most active antennas use as antenna parts of minimal conducting area, e.g. a small whip, connected to the active component (usually FET
). The signal attenuation caused by the antenna size to wavelength
mismatch, is compensated by a circuit, which consists of an impedance translating and an optional amplification device. This arrangement is especially useful for constructing compact low frequency
antennas which, due to budgetary, spacial or practical (installation in vehicles) requirements, must be downsized, the wavelengths involved ranging from one to ten kilometers.
Power for the active components may be supplied by batteries
, a filtered power supply
, or through the signal feeder itself. Antennas containing impedance translating and optionally amplifying components are usually used only for receiving, since their operation is of unidirectional nature.
Antenna (radio)
An antenna is an electrical device which converts electric currents into radio waves, and vice versa. It is usually used with a radio transmitter or radio receiver...
that contains active electronic components. This allows the construction of antennas of limited size and / or wide frequency range. Most active antennas use as antenna parts of minimal conducting area, e.g. a small whip, connected to the active component (usually FET
Field-effect transistor
The field-effect transistor is a transistor that relies on an electric field to control the shape and hence the conductivity of a channel of one type of charge carrier in a semiconductor material. FETs are sometimes called unipolar transistors to contrast their single-carrier-type operation with...
). The signal attenuation caused by the antenna size to wavelength
Wavelength
In physics, the wavelength of a sinusoidal wave is the spatial period of the wave—the distance over which the wave's shape repeats.It is usually determined by considering the distance between consecutive corresponding points of the same phase, such as crests, troughs, or zero crossings, and is a...
mismatch, is compensated by a circuit, which consists of an impedance translating and an optional amplification device. This arrangement is especially useful for constructing compact low frequency
Low frequency
Low frequency or low freq or LF refers to radio frequencies in the range of 30 kHz–300 kHz. In Europe, and parts of Northern Africa and of Asia, part of the LF spectrum is used for AM broadcasting as the longwave band. In the western hemisphere, its main use is for aircraft beacon,...
antennas which, due to budgetary, spacial or practical (installation in vehicles) requirements, must be downsized, the wavelengths involved ranging from one to ten kilometers.
Power for the active components may be supplied by batteries
Battery (electricity)
An electrical battery is one or more electrochemical cells that convert stored chemical energy into electrical energy. Since the invention of the first battery in 1800 by Alessandro Volta and especially since the technically improved Daniell cell in 1836, batteries have become a common power...
, a filtered power supply
Power supply
A power supply is a device that supplies electrical energy to one or more electric loads. The term is most commonly applied to devices that convert one form of electrical energy to another, though it may also refer to devices that convert another form of energy to electrical energy...
, or through the signal feeder itself. Antennas containing impedance translating and optionally amplifying components are usually used only for receiving, since their operation is of unidirectional nature.