Abstract
The initial experimental results of asymmetric mode competition in an X-band dual-mode relativistic backward wave oscillator (RBWO) operating at the low magnetic field are presented. In the experiment, the use of receiving antennas with different polarization directions allows direct determination of asymmetric mode, and the asymmetric mode with a frequency of 10.27 GHz is excited, which is in good agreement with the particle-in-cell (PIC) simulation results. Judging from that, the competition mode is asymmetric EH $_{\text{21}}$ mode. The asymmetric mode competition mechanism in the device is investigated theoretically. It is shown that the drift length plays a key role in the suppression and excitation of the asymmetric mode, validated by the experiment and the PIC simulation.