In telecommunication

Telecommunication

Telecommunication is the transmission of information over significant distances to communicate. In earlier times, telecommunications involved the use of visual signals, such as beacons, smoke signals, semaphore telegraphs, signal flags, and optical heliographs, or audio messages via coded...

, antenna noise temperature is the temperature of a hypothetical resistor at the input of an ideal noise-free receiver that would generate the same output

Output

Output is the term denoting either an exit or changes which exit a system and which activate/modify a process. It is an abstract concept, used in the modeling, system design and system exploitation.-In control theory:...

 noise power

Noise power

In telecommunication, the term noise power has the following meanings:# The measured total noise per bandwidth unit at the input or output of a device when the signal is not present.# The power generated by a random electromagnetic process....

 per unit bandwidth as that at the antenna

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...

 output at a specified frequency

Frequency

Frequency is the number of occurrences of a repeating event per unit time. It is also referred to as temporal frequency.The period is the duration of one cycle in a repeating event, so the period is the reciprocal of the frequency...

.

Antenna noise temperature has contributions from several sources:

• • Galactic radiation
  • Earth heating
  • The sun
  • Electrical devices
  • The antenna itself

Galactic noise is high below 1000 MHz. At around 150 MHz, it is approximately 1000K. At 2500 MHz, it has leveled off to around 10K.

Earth has an accepted standard temperature of 290K.

The level of the sun's contribution depends on the solar flux. It is given by

where is the solar flux,

is the wavelength,

and is the gain of the antenna in decibels.

The antenna noise temperature depends on antenna coupling

Coupling (electronics)

In electronics and telecommunication, coupling is the desirable or undesirable transfer of energy from one medium, such as a metallic wire or an optical fiber, to another medium, including fortuitous transfer....

to all noise sources in its environment as well as on noise generated within the antenna. That is, in a directional antenna, the portion of the noise source that the antenna's main and side lobes intersect contribute proportionally.

For example, a satellite antenna may not receive noise contribution from the earth in its main lobe, but sidelobes will contribute a portion of the 290K earth noise to its overall noise temperature.