  A new elementary mechanism of radiation due to the oscillatory character of a
radiation reaction force appearing when a relativistic charged particle moves
along a periodic structure without external fields is investigated. It is shown
that the non-synchronous spatial harmonics of Cherenkov-type radiation (CR) can
give rise to the oscillation of a particle which consequently generates
undulator-type radiation (UR). In the spectral region, where the diffraction of
generated waves is essential, the radiation manifests itself in the coherent
interference of CR and UR. A pure undulator -type radiation takes place only in
the wavelength range where the wave diffraction can be neglected. In the case
of coherent UR by a bunch of N electrons, the UR power is proportional to N in
the forth degree.
