Planar contra-wound helix for application in TWTs with reduced backward-wave oscillation

Backward-wave oscillation is frequently a problem in TWT amplifiers that use the conventional circular helix slow-wave structure (SWS). Circular contra-wound helix SWS, proposed in the past to solve this problem, is hard to fabricate at high frequencies. In this paper, we propose a planar contra-wound planar helix SWS with potential for microfabrication. It is shown with the help of simulated dispersion characteristics that the proposed structure decreases the risk of backward-wave oscillation in a TWT. Also presented is a proof-of-concept low frequency design of the proposed structure that can be fabricated using printed circuit techniques.