A High-Power and Broadband G-Band Extended Interaction Klystron Based on Mode Overlap

A
${G}$
-band multigap extended interaction klystron (EIK) adopting mode overlap method with ladder-type structure is proposed to achieve high power, high efficiency, and broad bandwidth. The gap number is set larger than the conventional EIK to achieve its potential. The high-frequency characteristics of the modes in output cavity are studied. The length ratio of long and short slots is optimized to obtain appropriate mode frequency interval and effective characteristic impedance. In our scheme, the gap number of output cavity is determined as 17 with the mode overlap of
$\pi $
mode and
$15/ 16\pi $
mode. The circuit structure and working conditions are carefully designed and optimized to solve the problem of instability under large gap number. With a beam current of 0.3 A, a voltage of 15.8 kV, and a magnetic field of 0.75 T, the particle-in-cell simulation shows that with the increase of frequency, the output cavity can work with two modes overlap and expand the 3-dB bandwidth to 1.32 GHz, which is more than two times of our previous work. Also, a maximum output power of 870 W, an efficiency of 18.4%, and a gain of 46.4 dB are finally obtained. The numerical simulation results definitely demonstrate the feasibility of mode overlap and its ability to the expansion of EIK bandwidth in the terahertz band.