Modeling of a vane-loaded helical slow-wave structure for broad-band traveling-wave tubes

A model of a vane-loaded helical slow-wave structure (SWS), in which an infinite number of vanes (INV) of infinitesimal thickness is considered, is improved. The modified INV (MINV) model takes into account the effect of the finite number and angular thickness of the vanes. This is done by suitably modifying the radial vane dimension on the basis of the interpretation of the data on the penetration of the axial electric field beyond the tips of the vanes into the intervane region as a function of the SWS parameters, including the number and angular extent of vanes. The theoretical dispersion characteristics obtained from both the INV and MINV models are compared to theoretical and experimental results published elsewhere. The INV model is found to be suitable for a structure with a relatively larger number of vanes. The study shows the superiority of the MINV over INV model in practical situations, wherein relatively fewer vanes of finite angular thickness are used. Methods to estimate the characteristic as well as interaction impedance of the structure, under the INV model approximations, are indicated