  We analyze radiation from a bunch that uniformly moves in a circular
waveguide and crosses the boundary between two areas: with a corrugated wall
and with a smooth wall. It is assumed that the corrugation period is much less
than the wavelengths under consideration. However, in difference with our
pervious works, the corrugation depth is of the same order as the wavelength.
The influence of corrugation on the electromagnetic field is investigated using
the method of equivalent boundary conditions. At first, we consider a regular
corrugated waveguide. Then two cases of the waveguides with boundaries between
the corrugated and smooth regions is studied: first, when the bunch flies out
of the corrugated part into the smooth one, and second, when the bunch flies
into the corrugated part from the smooth one. We obtain and analyze the
analytical expressions for the field components in both areas and reveal the
main physical peculiarities of the bunch radiation.
