  This paper outlines a method of obtaining the relation between the singly
scattered signal and the Fourier-spectrum of medium dielectric permititvity
fluctuations, with due regard for the fact that the scattering volume is
determined by antenna patterns and is not small. On the basis of this equation
we obtained the radar equation relating the scattered signal spectrum to the
spatial spectrum of fluctuations. Also, a statistical radar equation is
obtained, which relates the mean statistical power of the scattered signal to
the spectral density of the dielectric permitivity fluctuations without a
classical approximation of the smallness of the irregularities spatial
correlation radius. The work deals with the bistatic sounding case, when the
exact forward and exact backward scattering are absent, and sounding signal
have sufficiently norrow spectral band for scattered volume to change slowly on
ranges of Fresnel radius order. The statistical radar equations obtained
differs from the classical ones in the presence the coherent structures with
big correlation radii, and so the received signal spectrum can differ from
intrinsic spectrum of irregularities.
