Analysis and synthesis of slow wave structures for millimetre wave TWTs

Waring, Rob (2020) Analysis and synthesis of slow wave structures for millimetre wave TWTs. PhD thesis, Lancaster University.

Text (2020rwaringphd)
2020rwaringphd.pdf - Published Version
Available under License Creative Commons Attribution.
Download (6MB)

Abstract

Traveling wave tubes (TWTs) and backward wave oscillators (BWOs) are the only solution for high power amplification and RF generation at millimetre waves and THz frequencies. With advances in microfabrication technology, it is now possible to realise these devices with dimensions to support those frequency regimes. Promising applications of millimetre wave TWTs are as high-power amplifiers for wireless communications systems, imaging and satellite communications. BWOs would enable new plasma diagnostic in nuclear fusion capabilities and high-resolution imaging. TWTs are usually constructed using a helical waveguide as slow wave structure (SWS) by which wave energy can propagate. However, fabrication of a helix small enough to support mm-wave is not feasible. Novel SWSs are required suitable to be fabricated with the available processes. The challenge of the simulation of TWTs or BWOs utilising a new SWS is the lack of fast code and the need to rely on powerful, yet slow, 3D electromagnetic software, which are computationally intensive. Both helices and the coupled cavity TWT can be simulated by fast simulation codes using Lagrangian methods. One of the aims of this thesis is to create a fast code for simulating arbitrary three-dimensional SWS, in particular the double corrugated waveguide. The code was validated by comparison with data of a Ka-band TWT available in literature. The second aim is the design of circuits based on double corrugated waveguide SWSs for TWTs and BWO at different frequency to enable different applications. New topologies of couplers were investigated. Extensive 3-dimensional simulations were performed to define dimensions and performance at different frequency bands.