An extensive study aiming at analyzing the effect of rod shapes and dimensions on the gain of helix traveling wave tubes (TWT's) is performed. The evaluation of tube small-signal gain is obtained by making use of a rigorous field analysis which takes into account the helix tape model and the dielectric inhomogeneous loading conditions. Computing time to perform the analysis is extremely low compared with the time required in the case of a full wave, three-dimensional (3-D) electromagnetic simulator. The accuracy of the simulation approach has been extensively verified in a previous paper, A novel expression for the attenuation constant has been introduced in the model to improve the quality of results.

The proposed study allows a better understanding of tube behavior before fabrication highlighting the contribution of the shape, the mechanical tolerances and the epsilon(r) variation of the rods to the small-signal gain.