95 GHz helical TWT design

The helical slow-wave circuit is an attractive choice for traveling wave tube amplifiers (TWTAs) because of its inherently large bandwidth and relatively high RF efficiency. Unfortunately, as the operational frequency increases beyond Q-or V-band, its use has been limited by conventional fabrication techniques, and by the difficulty of passing enough current through the center of such a small structure. This paper describes the design and fabrication status of a 95 GHz TWT using microfabrication technology to create and assemble the helix. The electron beam propagates as two kidney shaped beamlets between the helix outer diameter and barrel.