Hybrid TEM waveguide mode

In the hybrid TEM or dual surface-wave mode in a strip-line waveguide with polythene-coated-copper boundary walls, the attenuation along the guide is independent of the relative thicknesses of the coatings for the same total thickness, contrary to the idea that when they are unequal the attenuation can be markedly less than for the quasiTEM mode with no dielectric.