Abstract: A dielectric waveguide consists of dielectric strips sandwiched between two parallel conductive plates whose inner surfaces are covered with thin dielectric layers. The other space of the waveguide is filled with an appropriate dielectric medium which can be air or any other low loss dielectric material whose dielectric constant is smaller than that of the dielectric strips. In this waveguide, radiated waves which might be generated at the curved sections and any other discontinuities of the dielectric strips can almost completely be suppressed due to the cutoff property of the conductive plates, if the electric field of electromagnetic waves to be transmitted is polarized primarily parallel to the conductive plates and relevant parameters of the waveguide are chosen to satisfy the following inequality: ##STR1## where .epsilon..sub.