Impedance analysis of tape-helix slow-wave structures

This paper reported an investigation about the interaction impedance behavior for slow-wave structures (SWS) in order to provide some guidelines to aid on traveling-wave tubes (TWT) and backward-wave oscillators (BWO) design. The analysis is made rigorous by removing the usual approximation of considering the radial propagation constant to be the same in the different structure regions. Furthermore, a tape-helix model instead of a simpler sheath-helix model has been used to consider the space-harmonic effects on the interaction impedance. Functional variations are given of interaction impedance with frequency and with the effective relative dielectric constant of support rods. Additionally, the dispersion equation is solved for the first backward-mode and its interaction impedance curve is shown.