In this paper, the investigations of the rectangular dielectric waveguides with embedded metallic discontinuities in millimeter waves (70-130 GHz) region have been presented. The full wave simulation of the structure has been carried out using frequency division time domain method. The frequency response of the structure shows that it can be used in designing of a dielectric filter in the given frequency range. The graphical representations of scattering parameters have been given for different values of the height of the dielectric rod and for the changes in the permittivity of the rod.