Attenuation in corrugated circular waveguides. Part 1: Theory

A study of the propagation behaviour of corrugated circular waveguides is described. The phase and attenuation characteristics are obtained using space harmonics in the interior and higher order modes in the slot region of the waveguide. It is found that only the first pair of harmonics and higher modes have a significant effect on the propagation behaviour. The HE11 mode, which is required in antenna applications, is shown to have an attenuation coefficient which is lower than that of any other mode, lower in fact than that of the TE010 mode in a smooth wall circular waveguide of comparable size. An investigation of the fields and currents in the waveguide aids a physical understanding of the phenomenon, which is shown to be only weakly sensitive to the waveguide tolerances. Experimental results to confirm the theory are given in Part 2 of the paper (see p. 1180).