The capability of efficient millimeter and submillimeter wavelength generation in Cherenkov like oscillators with multistage grating is discussed in this paper. The prototype of W-band oscillator with nonuniform grating has been presented. The dispersion calculations of the multistage grating in the waveguide and coupling impedance have been carried out. The simulations of self electric fields distribution of the wave-guide loaded by multistage grating were performed.