  The quadratic scalar radar equations are obtained for SuperDARN radars that
are suitable for the analysis and interpretation of experimental data. The
paper is based on a unified approach to the obtaining radar equations for the
monostatic and bistatic sounding with use of hamiltonian optics and ray
representation of scalar Green's function and without taking into account the
polarization effects. The radar equation obtained is the sum of several terms
corresponding to the propagation and scattering over the different kinds of
trajectories, depending on their smoothness and the possibility of reflection
from the ionosphere. It is shown that the monostatic sounding in the media with
significant refraction, unlike the case of refraction-free media, should be
analyzed as a combination of monostatic and bistatic scattering. This leads to
strong dependence of scattering amplitude on background ionospheric density due
to focusing mechanism and appearance of new (bistatic) areas of effective
scattering with significant distortion of the scattered signal spectrum.
Selective properties of the scattering also have been demonstrated.
