Improvement of Output Power and Bandwidth for Terahertz Extended Interaction Klystron With Multiple Resonance Cavities

In this article, an extended interaction klystron (EIK) in a terahertz band with high power, high efficiency, and wide bandwidth based on a mode overlap scheme and multiple resonance cavities is proposed. The high-frequency characteristics and electric field distribution of modes in 17-gap cavity are analyzed. And
$\pi $
mode and 15/
$16\pi $
mode are selected as the two adjacent working modes to realize mode overlap to expand the bandwidth. The number of cavity gaps and the length ratio of long and short slots are carefully optimized to achieve the appropriate frequency interval between modes. Then the sensitivity analysis of key parameters requires that the processing tolerance of the circuit should not exceed
$5~\mu \text{m}$
. The stability of the circuit is analyzed by using the normalized electronic conductance to ensure that the circuit will not produce oscillation. Finally, with the conditions of 0.3-A current, 18.5-kV voltage, and 0.02-W input power for the designed G-band six-cavity EIK, the PIC simulation results shows that the mode overlap can be achieved in different cavities, and the circuit can obtain a power of 740 W, a gain of 45.68 dB, a 3-dB bandwidth of 1.92 GHz, and an efficiency of 13.3%. The power, bandwidth, and efficiency have obvious improvement compared with other reported EIKs in the same frequency band. In addition, the consistency of the simulation results trend between AJDISK and CST also proves that the circuit we designed is reliable and feasible for the terahertz band EIKs with high performance in the future.