An active antenna is an
antenna
Antenna ( antennas or antennae) may refer to:
Science and engineering
* Antenna (radio), also known as an aerial, a transducer designed to transmit or receive electromagnetic (e.g., TV or radio) waves
* Antennae Galaxies, the name of two collid ...
that contains active electronic components such as
transistors, as opposed to most antennas which only consist of passive components such as metal rods,
capacitors and
inductors. Active antenna designs allow antennas of limited size to have a wider frequency range (
bandwidth) than passive antennas, and are primarily used in situations where a larger passive antenna is either impractical, such as inside a portable radio or on a vehicle, or impossible, such as in a suburban residential area with restrictions on large outdoor antennas.
Most active antennas consist of a short conventional antenna, such as a small
whip antenna, connected to an active component (usually a
FET). The active circuit compensates for the signal attenuation caused by the mismatch between antenna size and signal
wavelength. The active circuit consists of an impedance translating stage and an optional amplification stage. This arrangement is especially useful for constructing
low frequency
Low frequency (LF) is the ITU designation for radio frequencies (RF) in the range of 30–300 kHz. Since its wavelengths range from 10–1 km, respectively, it is also known as the kilometre band or kilometre wave.
LF radio waves exh ...
antennas which, due to budgetary, spatial, or practical requirements, must be kept compact.
Power for the active components may be supplied by
batteries
Battery most often refers to:
* Electric battery, a device that provides electrical power
* Battery (crime), a crime involving unlawful physical contact
Battery may also refer to:
Energy source
*Automotive battery, a device to provide power t ...
, a filtered
power supply, or through the signal feeder itself (
phantom power).
[Poole, Ian D. "Antenna Systems." Newnes Guide to Radio and Communications Technology. Amsterdam ; London: Newnes, 2003. Print.
] Antennas containing active impedance translating and (optionally) amplifying stages are usually used only for receiving, since operation of such stages is unidirectional.
See also
*
Smart antenna
References
Ulrich L. Rohde: Active Antennas,
RF Design, May/June 1981
{{reflist
Antennas (radio)
Radio frequency antenna types
Radio electronics
Television terminology