Anyone dealing with antennas and noise should read the classic 1946 paper by Dicke: http://www.eng.yale.edu/rslab/internal/Papers/dickepaper.pdf http://www.eng.

Anyone dealing with antennas and noise should read the classic 1946 paper by Dicke: http://www.eng.yale.edu/rslab/internal/Papers/dickepaper.pdf http://www.eng.yale.edu/rslab/internal/Papers/dickepaper.pdf tl, dr: One puzzler is that antenna radiation is frequency dependent, while that of Johnson noise in the microwave regime is flat with frequency. Then, considering detailed balance, how does an antenna matched to a terminated coax cable establish thermal equilibrium with space? What happens is that the 1/f^2 of the antenna pattern is cancelled by the f^2 (in the long-wavelength regime) of the Rayleigh-Jeans blackbody radiation formula.