A metallized dielectric waveguide filter includes an upper metallized dielectric waveguide having a plurality of upper resonant cavities, the upper metallized dielectric waveguide comprising an upper dielectric block having metallized outer walls, and a lower metallized dielectric waveguide having a plurality of lower resonant cavities, the lower metallized dielectric waveguide comprising a lower dielectric block having metallized outer walls. A first of the upper resonant cavities is operatively connected to a first of the lower resonant cavities via at least one coupling window. A first slot having metallized walls is provided in a portion of the upper dielectric block that is part of the first of the upper resonant cavities.