antenna temperature


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antenna temperature

A measure of the strength of signal received by a radio telescope from a radio source. It is defined as the noise power received per unit bandwidth, divided by the Boltzmann constant, k . Antenna temperature depends on the surface brightness of the sky weighted by the telescope's beam rather than physical temperature of the antenna. A radio source of flux density S with an angular diameter that is much smaller than the antenna's beam will give an antenna temperature of SA e /(2k ), where A e is the effective area (see array) of the antenna. If the beam is filled by a uniform source of brightness temperature T B, the antenna temperature will also be T B .

Synchrotron emission from cosmic rays in the Galaxy produces a diffuse radio emission centered broadly on the galactic plane. Any practical observation of a radio source has to be made against this background emission, which at low frequencies limits the sensitivity of the radio telescope. The antenna temperature of the diffuse emission is called the background temperature; the electrical noise it produces in radio receivers is often called cosmic noise.

antenna temperature

[an′ten·ə ‚tem·prə·chər]
(electromagnetism)
The temperature of a blackbody enclosure which would produce the same amount of noise as the antenna if it completely surrounded the antenna and was in thermal equilibrium with it.
References in periodicals archive ?
Step 4: By going through all ray-tracing path of the beam range by repeating Step (2) and Step (3), the total radiation temperature received by the antenna can be calculated as per Equation (6), which is substituted into Equation (2) to obtain the value of the antenna temperature at the moment [t.
k] + i[DELTA]t, and repeat the calculation from Step (2) to Step (4), so as to get the curve of the antenna temperature during the intersection of the radiometer and the target.
a] is the measured increase in antenna temperature due to the source (K) and [[Eta].
Taking the reverse radiation noise into account, the antenna temperature contrast can be rewritten through substituting Equations (9) and (10) into Equation (8), and the result is:
Additionally, the first part in Equation (11) reveals the specific influence on antenna temperature contrast resulted from the reverse radiation noise, and it is list as below:
1] The opposite is true when the effective antenna temperature is high relative to 290 K, as may be the case in dense urban environments where significant man-made noise and ground clutter exist.
Bundy, "Noise Figure, Antenna Temperature and Sensitivity Level for Wireless Communication Receivers," Microwave Journal, Vol.
The greatest portion of the effective antenna temperature is contributed by emissions and reflections from the ground and other physical obstacles.
The relationships described previously represent the equivalent noise temperature of the various sources that contribute to the effective antenna temperature.
The anticipated antenna temperature in each case can be obtained by introducing the apparent brightness temperature in Equation 1.
By using the radiometer not to measure directly the antenna temperature, but rather the difference between this and some known reference temperature, the sensitivity of the measurement to gain and noise temperature instabilities is greatly reduced.
A high-gain antenna aimed directly at the sun will have a large antenna temperature.