Round Waveguide with Double Lining

Transmission of the TEoi wave in round waveguide is degraded by manufacturing and laying imperfections. 1 To reduce the effects of mode conversion at manufacturing imperfections, mode filters are required. To reduce the effects of laying curvature, the phase constant of the TMu wave must be made different from the TEoi phase constant. Instead of using mode filters, lining the waveguide wall with a thin layer of dissipative material has been suggested.2,3 Lining the waveguide with a low-loss material reduces the bending effects.4 A waveguide with a double lining was proposed by S. E. Miller to solve both problems. A base layer of dissipative material mainly introduces mode filtering, and a top layer of low-loss material changes the T M U phase.