Design of a tapered helix for suppressing backward wave oscillations in MMW TWT’s

Backward wave oscillations are easy occurred in high power helix millimeter wave traveling wave tubes (MMW TWT’s), owing to larger ka value and higher operating voltage. The start current of backward wave is calculated for helix TWT in Ka band. It is shown that start current will increase by used a tapered helix. Backward wave oscillations can be suppressed in tube. The design method of the tapered helix is given in this paper.