Effect of inhomogeneity on backward wave in a helix TWT

In the inhomogeneously loaded helical slow-wave structure (SWS), the helix is supported by rectangular/circular and/or arbitrary shaped dielectric support geometry and the whole is enclosed in a metal envelope. In this paper, the authors present theoretical results obtained from GANGA (Ghosh´s analysis with non-uniform GamaA for helix TWTs), to predict and control the potential backward-mode oscillation in a TWT for a wide range of structure parameters. It has been found that with the increase in structure inhomogeneity, the backward phase velocity and backward impedance increases with frequency but forward (fundamental) phase velocity and impedance (fundamental) decreases. Also the other structure parameters, namely, position of the metal envelope, helix pitch angle, helix tape thickness, etc, control the backward wave propagation. However, the effect of structure inhomogeneity is more pronounced.