Every object with a physical temperature above absolute zero radiates energy. The amount of energy radiated is usually represented by an equivalent temperature.
If an antenna maintained at a certain physical temperature (Tp) is connected to a receiver by a length of transmission line (L), with a constant temperature (To) throughout, and having uniform attenuation (α), the effective antenna temperature at the receiver terminal is:
The parameters used in the equation are:
Tant = antenna temperature at the receiver terminals (K)
Ta = antenna noise temperature at the antenna terminals (K)
TAP = antenna temperature at the antenna terminals due to physical temperature (K)
Tp = antenna physical temperature (K)
α = attenuation coefficient of transmission line (Np/m)...
εA = thermal efficiency of the antenna
L = length of the transmission line (m)
To = physical temperature of the transmission line (K)