Analysis of BWO start oscillation condition in the practical TWT

Summary form only given. Attenuator or sever always exists in a practical traveling-wave tube (TWT) for improving gain and suppressing the oscillation, including backward-wave oscillation (BWO). The influencing factors include start position and length as well as attenuation quantity of the attenuators. In the event that the attenuator or sever was considered, a linear theory was employed to analyze BWO start oscillation condition. Numerical results show that the start oscillation length is decreasing when the start position of the attenuator is close to the input section. Start oscillation current of the output section is increasing as the attenuation length decreasing, or the attenuation quantity increasing.