Impact of Microfabrication Processes on Surface Roughness for sub-THz devices for 6G Wireless Networks : A Thesis Submitted for the Partial Fulfilment of a Masters Degree in Engineering, by Research

Da Costa, Vincent and Paoloni, Claudio and Rennie, Allan and Letizia, Rosa (2026) Impact of Microfabrication Processes on Surface Roughness for sub-THz devices for 6G Wireless Networks : A Thesis Submitted for the Partial Fulfilment of a Masters Degree in Engineering, by Research. Masters thesis, Lancaster University.

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Abstract

Traveling wave tubes (TWTs) are devices used to amplify electromagnetic signals using high power electron beams to achieve higher frequency bandwidths granting access to Sub-THz frequencies and thus increasing the range and rate at which data can be transmitted over wireless networks. TWTs can serve for a variety of different applications in a range of sectors, including telecommunications, security/military, medical and science industries. As a result of the devices high-power output achievable and the range of applications, TWTs have over time gained a lot of interest; however, the fabrication challenges and costs of their production have resulted in their usage being relatively small scale. This thesis discusses the fabrication aspects of a W-Band (102-109.5GHz) TWT and focuses specifically on the enhancement and recommendations of machining processes for the Double Corrugated Waveguide (DCW) Slow Wave Structure (SWS). This design ensures effective interaction between the Radio Frequency (RF) signal and the electron beam whilst offering more accessible fabrication methods. This device which will be used in the telecommunications sector will allow for high-capacity terrestrial links in the form of 6G wireless networks, offering a greater coverage area and data transfer rate not achievable with the currently used solid state amplifiers. The primary aim of this research was to provide a procedure to enhance the precision of the machining processes, specifically with regards to minimising the levels of surface roughness within the DCW. This would ensure it works with maximum efficiency by achieving the lowest possible amount of transmission loss. The tolerances required from the structure as well as complexities and small sizes of the design necessitate the use of micro-tooling throughout the manufacturing process, as well as high speed machining technology solutions by using an Air Turbine Spindle to meet tooling speed requirements. With the ambition of producing a large quantity of TWTs to support a range of bandwidths in the wireless market, it is essential to find reliable methods of reducing the cost per unit in the production process. As a result, some attention was dedicated to the optimisation of the manufacturing processes to reduce the lead time of the DCW structure, as well as extending tool life.