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

• Published in: IEEE transactions on microwave theory and techniques Vol. 68; no. 11; pp. 4554 - 4559
• Main Authors: Wang, Weijie, Liu, Guo, Jiang, Wei, Pu, Youlei, Wang, Jianxun, Luo, Yong
• Format: Journal Article
• Language: English
• Published: New York IEEE 01.11.2020; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Bandwidth; Bandwidths; Broadband; Cavity resonators; Circular TE₁₁ mode; compact structure; Couplers; Couplings; gyrotron traveling wave tube (gyro-TWT); input coupler; Microwave measurement; Rectangular waveguides; Superhigh frequencies; Transmission efficiency; Traveling wave tubes; Traveling waves
• ISSN: 0018-9480; 1557-9670
• DOI: 10.1109/TMTT.2020.3016305

Design and measurement of a broadband compact circular TE 11 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 <inline-formula> <tex-math notation="LaTeX">S_{11} </tex-math></inline-formula> is less than −10 dB within 7.9-9.93 GHz. Also, the split transmissions <inline-formula> <tex-math notation="LaTeX">S_{21} </tex-math></inline-formula> and <inline-formula> <tex-math notation="LaTeX">S_{31} </tex-math></inline-formula> 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 TE 11 mode input coupler had been applied in our X-band gyro-TWT design.