Abstract - In the millimeter-wave and terahertz frequency range, the folded waveguide
(FWG) is a typical slow-wave structure employed in traveling wave tube (TWT) design,
as the structure offers broad bandwidth and moderate output power. The full-metal
circuit also has advantages, such as high-power handling capability, making the FWG
TWT a vital radiation source for near-terahertz applications. A FWG slow-wave structure
circuit for a compact E-band sheet beam traveling wave tube amplifier has been
designed, fabricated, and cold tested. The circuit is compatible with sheet electron
beams and predicted to produce high output power with reduced beam current density,
hence suitable for periodic permanent magnet focusing and lower voltage operation.
The optimized SWS can fulfill the 5 GHz (81 – 86 GHz) bandwidth requirement while
avoiding backward wave oscillation. A multi-step, side-out coupler is designed to be
compatible with the planar periodic magnetic focusing system. A cold test was
performed to verify the circuit performance.