  Radiation generated by a charge moving through a vacuum channel in a
dielectric cone is analyzed. It is assumed that the charge moves through the
cone from the apex side to the base side (the case of "inverted" cone). The
cone size is supposed to be much larger than the wavelengths under
consideration. We calculate the wave field outside the target using the
"aperture method" developed in our previous papers. Contrary to the problems
considered earlier, here the wave which incidences directly on the aperture is
not the main wave, while the wave once reflected from the lateral surface is
much more important. The general formulas for the radiation field are obtained,
and the particular cases of the ray optics area and the Fraunhofer area are
analyzed. Significant physical effects including the phenomenon of "Cherenkov
spotlight" are discussed. In particular it is shown that this phenomenon allows
reaching essential enhancement of the radiation intensity in the far-field
region at certain selection of the problem parameters. Owing to the "inverted"
cone geometry, this effect can be realized for arbitrary charge velocity,
including the ultra relativistic case, by proper selection of the cone material
and the apex angle. Typical radiation patterns in the far-field area are
demonstrated.
