Field theoretic methods for modeling the finite thickness of helix slow-wave structures

A new tape helix model is introduced in which the field components in the infinitesimally thick helical-gap between helix tape turns are expanded in terms of the so-called helical-harmonics (TE mode). The actual helix is replaced by an infinitely thin tape helix placed at its mean radius and the space between the actual helix outer radius and the modeling tape is filled with vacuum as done in Swift-Hook´s method. Results obtained by the proposed method shows better agreement to experimental data in comparison with ones obtained by using the conventional helical-harmonics approximation.