The number of degrees of freedon of a surface S for incoherent radiation taking into account both polarizations was established on the basis of Jeans thermodynamic considerations n1 2pisLambda sq. The number of degrees of freedom of microwave radiation from a surface S coherent, polarized optics was also established using two different methods. This number is n 4pisNu sq. One should note that these two methods are related although the phase is not involved in incoherent radiation. The above considerations are applied to beams of limited spatial extent. Author
Trans. of Applied Optics v4 n10 p1317-9 1965, tr. by William J. Grimes.