Relative TE/TM eigenmode contents of hybrid modes in very overmoded circumferentially corrugated circular waveguides (ka=20-130 where k=27c/X, is the free-space propagation constant and a is the inner waveguide radius) with various shapes of corrugation have been calculated using a scattering matrix code. This computational technique includes all geometrical parameters of the corrugation profile and does not impose any restrictions. The influences of slot depth and corrugation period on the eigenmode mixture have been examined. Since the Hz-field of the TEii mode is nearly zero, the lowest order hybrid HEii mode can be described by a two-mode TEi i/TMii eigenmode combination whereas higher order hybrid modes contain several eigenmodes of the corresponding smooth-wall waveguide. For example, the EH15,2 mode at 140 GHz in a corrugated waveguide with an inner diameter I.D.=27.79 mm and resonant slots (depth d=X/4, period p=X/3) can be synthesized on the average by the following eigenmode mixture: TE15,2 (55 % power, 0Ã‚Â° phase), TM15,1 (26 %, 180Ã‚Â°), TE15,1 (10 %, 180Ã‚Â°), TM15,2 (7 %, 0Ã‚Â°), TE15,3 (1%, 0Ã‚Â°) and TM15,3 (0.5 %, 0Ã‚Â°).