Round waveguide with double lining

Doubly lining the walls of round waveguide with a base layer of dissipative material and a top layer of low loss material provides mode filtering for TE01 transmission and reduces TE01 loss in bends. The effects of thin layers are calculated as perturbations of the empty waveguide characteristics. For best performance, the dissipative layer should have low permittivity and high loss factor. The layers should be only a few mils thick.