Design and Measurement of a Broadband Compact TE11 Mode Input Coupler for an X-Band Gyrotron Traveling Wave Tube.

Design and measurement of a broadband compact circular TE11 mode input coupler for gyrotron traveling wave tubes (gyro-TWTs) are presented in this article. Different from the T-junction, Y-type, and multiple-hole input couplers, the proposed coupler has a merit of compact dimensions formed by the H-plane of a rectangular cavity. The simulation results show that the port reflection $S_{11}$ is less than −10 dB within 7.9–9.93 GHz. Also, the split transmissions $S_{21}$ and $S_{31}$ are over −3.4 dB in this band. It indicates that the relative bandwidth is 22.8%, and the transmission efficiency is higher than 90%. To further broaden the bandwidth, we propose an improved input coupler with ridges achieving an excellent bandwidth of 28.6%. The designed input coupler has been measured with open boundaries and matched output ports. The simulation and measurement results are in good agreement. The compact TE11 mode input coupler had been applied in our X-band gyro-TWT design. [ABSTRACT FROM AUTHOR]