A method of calculation is proposed and total energy losses in one round trip for lower EH1m, TE0m and TM0m modes are obtained numerically for diffraction mirror in the form of a circular diaphragm which placed inside a dielectric circular hollow waveguide. It is shown that the use of diffractive mirrors with large-scale irregularities in a dielectric waveguide resonator is the preferred among intracavity methods for obtaining of the polarization-nonuniform modes with azimuthal direction of polarization.