Terahertz Backward Wave Oscillator: A Review on Slow Wave Structure Designs, Performance Characterizations, and Fabrication Methods

The backward wave oscillator (BWO) is an important vacuum electron source that utilizes backward waves to interact with electron beam, resulting in high-frequency self-excited oscillations. Due to the negative dispersion property, self-excited oscillations, tunability, room-temperature operation, and relativistic effects, the BWO has significant application prospects in fields such as terahertz (THz) imaging and nuclear fusion. The development direction of BWO is high frequency and high power. This article jointly reviews the research progress of THz BWOs in the last decade from many aspects, such as the theory of BWO, slow wave structure (SWS) design, and common fabrication methods used in the THz band, and introduces the latest methods and mechanisms for improving the performance of BWOs. In addition, the latest progress of relativistic BWOs (RBWOs) and the applications of BWOs was also introduced. The above contents will help to understand the theoretical and experimental studies of BWOs and RBWOs and promote their practical applications in the fields of identification imaging and energy.