  The concept of exceptional point of degeneracy (EPD) is used to conceive a
degenerate synchronization regime that is able to enhance the level of output
power and power conversion efficiency for backward wave oscillators (BWOs)
operating at millimeter-wave and Terahertz frequencies. Standard BWOs operating
at such high frequency ranges typically generate output power not exceeding
tens of watts with very poor power conversion efficiency in the order of 1%.
The novel concept of degenerate synchronization for the BWO based on a folded
waveguide is implemented by engineering distributed gain and power extraction
along the slow-wave waveguide. The distributed power extraction along the
folded waveguide is useful to satisfy the necessary conditions to have an EPD
at the synchronization point. Particle-in-cell (PIC) simulation results shows
that BWO operating at an EPD regime is capable of generating output power
exceeding 3 kwatts with conversion efficiency of exceeding 20% at frequency of
88.5 GHz.
