TWT amplifiers remain the microwave power amplifiers of choice for high power microwave and mm-wave systems for land and aerospace applications. This book aims at advancing the present technology of TWTs with coupled resonator SWSs by enhanced analytical (quasi-TEM and equivalent circuit analysis) and field analysis codes, improved modeling, simulation and experimentation. Using these techniques, new variants of coupled resonator SWSs like ladder-core inverted slot mode SWS and the inductively loaded interdigital SWS have been investigated. The possibility of achieving both coalesced mode design that gives wide bandwidth and multibeam design that improves the peak power and gain is presented. An improved modeling and simulation technique using 3D electromagnetic codes has been proposed. A field analysis model for corrugated waveguide SWS, based on Coupled Integral Equation Technique (CIET), which is a combination of Mode Matching Technique (MMT) and Method of Moments is presented. The analysis will be very useful, especially to microwave engineers aiming to improve the TWT design for higher levels in power, efficiency and bandwidth.