The effect of conductivity losses on propagation through the helical slow-wave structure of a traveling-wave tube

A general theory has been developed to account for the material conductivity losses on the performance characteristics of a helical slow-wave structure (SWS) traveling-wave tube (TWT). The effects of helix/envelope conductivity have been studied on various propagation parameters, namely, the axial propagation constant, the interaction impedance, the attenuation constant, and the equivalent circuit resistance per unit length of the structure. While with the first two of these parameters, these effects are found to be only of the second order, they are quite significant for the remaining two. The functional dependence of the propagation parameters on the other structure parameters of importance namely, the relative permittivity of the helix supports, the envelope-to-helix separation, the helix pitch angle, and the thickness of the helix wire, has also been shown. The generalized theory developed here has been further tested by comparing the results with those obtained elsewhere for some special cases