Also found in: Acronyms.
antenna temperatureA 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.