Interaction impedance from the equivalent circuit parameters of a dielectric-loaded helical slow-wave structure of a traveling-wave tube

The interaction impedance of the dielectric-loaded helical slow-wave structure (SWS) of a traveling-wave tube (TWT), with or without a metal envelope, has been found by integrating the Poynting vector across the structure cross section. A simple empirical relation is then suggested to predict the value of the interaction impedance from the knowledge of the equivalent-circuit parameters of the structure without requiring the complex integration of the Poynting vector