Noise reduction in a travelling wave tube employing a helix input coupler

摘要

1,038,845. Travelling wave tubes. M-O. VALVE CO. Ltd., and C. H. DIX. July 23, 1965 [July 30, 1964], No. 30220/64. Heading H1D. A travelling-wave tube has a main wire helix slow wave structure, a further helix disposed coaxial with and connected in series with the main helix and an input coupler' consisting of a wire helix disposed coaxially surrounding the further wire helix, the arrangement being such that the phase velocity of electromagnetic waves along the further helix and the phase velocity along the main helix differ sufficiently so that within the pass-band of the device waves may interact with the beam along the main helix but waves of the same frequency do not interact along the further helix. The main and further helix preferably have the same diameter, the pitch of the further helix being greater than that of the main helix. Between the two helices a transition section is provided consisting of a helix of gradually decreasing pitch, the decrease obeying an exponential law. The helical couplers are located around the envelope of the tube. The main helix has attenuating portions consisting of an exterior lossy helix section. The noise figure of the device is reduced since noise is not amplified along the further helix.