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Investigation of asymmetric mode competition in a relativistic backward wave oscillator

The relativistic backward wave oscillator (RBWO) is one of the most important high-power microwave generators. Its stability and reliability must be further improved to meet the demands of key applications. The factors that limit its performance are varied but include radio frequency breakdown and mode competition. Based on a C-band RBWO, the mode competition was carefully analyzed and the effects on the performance of the RBWO were revealed. As shown in the studies, for an axisymmetric system, asymmetric mode competition probably still exists. Therefore, a three-dimensional particle-in-cell model was configured to investigate the mode competition. The theoretical and experimental results confirmed that the competing mode for a C-band RBWO was EH21. Changing the gap between the cathode and anode was found to be effective for suppressing the asymmetric mode.