radiance in the cavity is the same in any direction Radio waves are low enough in frequency so the Rayleigh–Jeans formula gives a very close approximation of the blackbody spectral radiance Therefore The Johnson–Nyquist noise power produced by a resistor at temperature over a frequency range is Since the cavities are in thermodynamic equilibrium , so See also Radiation pattern E-plane and H-plane References External links Isotropic Radiators, Matzner and McDonald, arXiv Antennas Antennas D.Jefferies isotropic radiator AMS Glossary U.S. Patent 4,130,023 - Method and apparatus for testing and evaluating loudspeaker performance Non Lethal Concepts - Implications for Air Force Intelligence Published Aerospace Power Journal, Winter 1994 Glossary Cosmic Microwave Background - Introduction Isotropic Radiators Holon Academic Institute of Technology Radiation Radio frequency antenna types Antennas (radio)