The
absolute gain of an antenna, for a given direction and
polarizationPolarization is a property of waves that describes the orientation of their oscillations. This article primarily covers the polarization of electromagnetic waves such as light, although other types of wave also exhibit polarization....
, is the ratio of (a) the
powerIn physics, power is the rate at which work is performed or energy is converted. It is an energy per unit of time. As a rate of change of work done or the energy of a subsystem, power iswhere P is power, W is work and t is time....
that would be required at the
inputInput is the term denoting either an entrance or changes which are inserted into a system and which activate/modify a process. It is an abstract concept, used in the modeling, system design and system expwdlfhaslfnasl'fnsfasnfloitation...
of an ideal
isotropic radiatorAn isotropic radiator is a theoretical point source of waves which exhibits the same magnitude or properties when measured in all directions. It has no preferred direction of radiation. It radiates uniformly in all directions over a sphere centred on the source. It is a reference radiator with...
to (b) the power actually supplied to the given antenna, to produce the same
radiant intensityIn radiometry, radiant intensity is a measure of the intensity of electromagnetic radiation. It is defined as power per unit solid angle. The SI unit of radiant intensity is watts per steradian . Radiant intensity is distinct from irradiance and radiant exitance, which are often called intensity...
in the far-field region.
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The
absolute gain of an antenna, for a given direction and
polarizationPolarization is a property of waves that describes the orientation of their oscillations. This article primarily covers the polarization of electromagnetic waves such as light, although other types of wave also exhibit polarization....
, is the ratio of (a) the
powerIn physics, power is the rate at which work is performed or energy is converted. It is an energy per unit of time. As a rate of change of work done or the energy of a subsystem, power iswhere P is power, W is work and t is time....
that would be required at the
inputInput is the term denoting either an entrance or changes which are inserted into a system and which activate/modify a process. It is an abstract concept, used in the modeling, system design and system expwdlfhaslfnasl'fnsfasnfloitation...
of an ideal
isotropic radiatorAn isotropic radiator is a theoretical point source of waves which exhibits the same magnitude or properties when measured in all directions. It has no preferred direction of radiation. It radiates uniformly in all directions over a sphere centred on the source. It is a reference radiator with...
to (b) the power actually supplied to the given antenna, to produce the same
radiant intensityIn radiometry, radiant intensity is a measure of the intensity of electromagnetic radiation. It is defined as power per unit solid angle. The SI unit of radiant intensity is watts per steradian . Radiant intensity is distinct from irradiance and radiant exitance, which are often called intensity...
in the far-field region.
If no direction is given, the absolute
gainGain is a measure of a system's response to feedback. If the gain in a positive feedback loop is less than 1, the feedback is not of itself sufficient to make the system become unstable. For example, water evaporating from the World's oceans causes a positive feedback, as it is a greenhouse gas...
of an antenna corresponds to the direction of maximum
effective radiated powerIn radio telecommunications, effective radiated power or equivalent radiated power is a standardized theoretical measurement of radio frequency energy using the SI unit watts, and is determined by subtracting system losses and adding system gains...
. Absolute gain is usually expressed in
dBThe decibel is a logarithmic unit of measurement that expresses the magnitude of a physical quantity relative to a specified or implied reference level. Since it expresses a ratio of two quantities with the same unit, it is a dimensionless unit...
.
Examples of absolute gain are no-load gain, full-load gain, and small-signal gain.