The Effect of Conductivity Losses on Propagation Through the Helical Slow-Wave Structure of a Traveling-Wave Tube

Abstract

A general theory has been developed to account for the material conductivity losses on the performance characteristics of a helical slow-wave structure. 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. The theoretical results obtained in both the sheath and the tape models have also been compared with experimental results available elsewhere. The agreement between theory and experiment is found to be much closer in the tape model developed here than in the sheath model tried by other workers. © 1988 IEEE