This lesson describes a parallel plate waveguide as composed of two conducting plates of the same width, w, separated by a distance, d, and filled with a dielectric. Analysis assumes that w is much greater than d, so that the majority of the field is contained within the dielectric. Parallel plate waveguides are easy to manufacture with no interference problems because the electric field is all internal. A rectangular wave guide is a rectangular conductive tube of width A and height B filled with a dielectric. The fields are entirely contained, so there is no external interference. Rectangular waveguides show extremely low loss performance, but they are also quite bulky and inflexible.