Electromagnetic field analysis of waveguide-dielectric phase shifter is discussed. It is shown that permittivity of dielectric material oppositely affects on required displacement of wide waveguide wall and phase shifter section length. Reducing of dielectric insertion loss in partially dielectric loaded waveguide is demonstrated. Minimum of the insertion loss depends on permittivity of dielectric, frequency as well as distance between wide waveguide wall and dielectric. Scattering problem for dielectric wedge located in rectangular waveguide is solved