TWTs at D-band (141 – 174.5 GHz) are the most promising solution to provide high transmission power for enabling
long range wireless links with high capacity at sub-THz frequency. A D-band TWT was designed in the 151-161.5 GHz
frequency band with about 10 W output power. The double corrugated waveguide is adopted as slow wave structure (SWS)
for the relatively easy fabrication and alignment in comparison to other SWSs typically used at sub-THz frequency. Due
to the short wavelength at D-band, the fabrication requires high precision computerised numerically controlled (CNC)
milling machining and tight tolerance control. The sensitivity analysis of performance as a function of the dimensions
of a device is an important method to predict in advance how the performance of the device is affected by geometry
variations, and also to ascertain the required level of fabrication accuracy to meet the specifications. The sensitivity
analysis is also useful to define the best initial dimensions for further optimization. This paper discusses the sensitivity
analysis applied to the double corrugated waveguide (DCW) to be used in a 151-161.5 GHz TWT. A broad range of
parameters are considered demonstrating the importance of fabrication accuracy and the eventual correction options
for a correct functioning. The impact of fillets in the DCW pillars is also evaluated to eventually ease the fabrication
requirement.