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The use of groove gap waveguide technology is proposed to aid the design of wide band slow wave structures for millimeter wave travelling wave tubes. The possibility to control the electromagnetic wave without the need for metal contact at the walls can facilitate the realization at high frequencies while increasing design flexibility.

The design of a W-band traveling-wave tube (TWT) power amplifier based on a groove gap waveguide slow wave circuit is presented in this paper. The technology of gap waveguide is analyzed to aid the design of electromagnetic band gap based slow wave structures in the upper millimeter wave range of the spectrum while alleviating some of the typical fabrication challenges at these frequencies. The results of Particle-In-Cell (PIC) simulations numerically demonstrate a 10-GHz instantaneous 3-dB bandwidth in the range 89-99 GHz with a minimum power gain of 25 dB. A prototype of the complete slow wave structure is manufactured via computer numerical control (CNC) machining and measured to verify the cold simulation results. Machining tolerances and surface roughness are also investigated. The design approach via groove gap waveguide is flexible and can be extended to alternative rectangular waveguide based slow wave structures.

Gap waveguides have been proposed for the design of slow wave structures (SWS) of travelling wave tubes (TWT) operating at the millimeter wave. In this paper, we consider a SWS based on a metal pin structure and top metal plate to realize the gap waveguide, loaded with a central corrugation for realizing the synchronism condition with the electron beam. Parametric studies are presented to show the impact of variation of certain critical dimensions of the SWS in order to analyze tolerances and optimization for a W-band TWT (87 -100 GHz).