  Coherent Smith-Purcell radiation generated by bunched electron beam in the
lamellar metal and dielectric gratings in the millimeter wavelength range was
compared theoretically and experimentally. For theoretical estimation a simple
model suitable for both dielectric and metal gratings was developed.
Experimental comparison was carried out using extracted bunched 6.1 MeV
electron beam of the microtron at Nuclear Physics Institute (Tomsk Polytechnic
University). Both theoretical estimations and experimental data showed the
difference of the radiation characteristics from the lamellar metal and
dielectric gratings. The radiation from the dielectric grating had peak
structure not monotonic one and was more intense comparing with metal grating
radiation in the wavelength less than coherent threshold. These differences may
be useful for research and development of new compact monochromatic radiation
sources in sub-THz and THz region.
