E.G.Bessonov**, Yu.Shibata*, S.Sasaki*, K.Ishi*, M.Ikezawa*
*RISM, Tohoku University, Japan; **Lebedev Physical Institute
The main consequences of the vector theory of excitation of resonators by electron beams are presented. Some features of excitation of the long
wavelength broadband radiation in open resonators of free-electron lasers
are discussed.