Improved Design and Microfabrication of H-Plane and E-Plane Loaded Rectangular Slow-Wave Structure for THz TWT Amplifier

This paper reports further investigation on a recently proposed H-plane and E-plane loaded slow-wave structure (SWS) for terahertz traveling-wave tube (TWT) amplifier. An improved input-output coupler is designed to enable easy fabrication by microfabrication technology, UV-lithography, electroplating, and molding (LIGA), and deep reactive-ion etching. The coupler shows very low reflection coefficient, S-11 < - 15 dB over a frequency range 360-450 GHz. To improve the beam-wave interaction and enhance the saturated output power of the TWT, the SWS with tapered design is implemented. By tuning the period, the wave is resynchronized with the beam at the end of the SWS, resulting in more than 60% increase in the saturated output power across the 80-GHz bandwidth. In addition, the sensitivity of the output power of the TWT to the fabrication tolerance of the individual geometrical parameters is also studied in detail. It is found that the output power reduces by 80% for approximately 2% variation in the synchronized beam voltage. The KMPR-based UV-LIGA technique is adopted to fabricate the H-plane and E-plane loaded SWS. The measured lateral dimensional accuracy within similar to 2 mu m and rms roughness of metal sidewall surface less than 80 nm is obtained.