Investigation of conductivity loss in a helix slow-wave structure due to the backward-wave space-harmonic propagation mode

Closed form expression for the inductance per unit length of the transmission-line equivalent circuit of a helical slow-wave structure was derived incorporating the effects of space-harmonic propagating modes and surface current density on the helix over the actual metallic area of the tape. This expression was used for estimating the conductivity loss in the structure following Wheeler´s incremental inductance rule. Some interesting characteristics that were observed on the conductivity loss due to the backward-wave space-harmonic mode are reported.