Imperfections in Lined Waveguide

Thickness variations of the lining and deformations of the cross-section couple circular electric waves to unwanted modes and degrade transmission characteristics. Generalized telegraphist's equations for lined waveguide with these imperfections are found. The most critical interaction is caused by lining variations of circular symmetry between TE01and higher circular electric waves. Because of such interaction the average TE01loss is increased and signal transmission is distorted. More serious than signal distortion is the increase in average loss. In2^I.D. copper waveguide with a0.01^lining, the rms of a typical thickness variation should stay below0.002^for the TE01loss at 55.5 kmc not to be raised more than 10 per cent. Cross-sectional deformations in lined waveguide cause nearly the same increase in loss and signal distortion as in plain waveguide. Tolerances for such deformations should therefore be the same as in plain waveguide.