A Mode-Suppression Circuit for the Ka-Band $\text{TE}_{01}$ Gyrotron Travelling Wave Tube: Design and Measurement

In this paper, the design and measurement of a mode-suppression circuit (MSC) applied in the nonlinear interaction region of a Ka-band gyrotron travelling wave tube (gyro-TWT) are presented. The proposed MSC is capable to suppress the spurious $\text{TE}_{11}$ mode with no influence on the operating $\text{TE}_{01}$ mode which helps to improve the tube stability for the high-power operation. Simulation result shows MSC can provide a loss of more than -5 dB around 23.1 GHz for the spurious $\text{TE}_{11}$ mode which agrees well with the measured results.