An Absorber-Wall Parallel-Plate Waveguide

The electromagnetic fields that can propagate through a parallel-plate waveguide having absorber walls are investigated, and it is shown that dominant TM^e₁₀ and TE^e₁₀ modes can propagate independently with both having a highly-tapered (cosine-type) transverse distribution, a phase velocity slightly exceeding the speed of light, and very low axial attenuation, especially for a wall-spacing large as compared to a free-space wavelength. In other words, such an absorber-guide acts life a corrugated waveguide having "lambda/4" teeth (balanced-hybrid mode) but it does so over virtually an unlimited bandwidth and with little sensitivity to the absorber\´s characteristics.