Investigation on a Broadband 220GHz Extended Interaction Klystron

Abstract

An extended interaction klystron, which is composed of an input cavity and an output cavity both based on 8 periods of staggered double rectangular waveguide structure (SDRWS) and an intermediate cavity based on 6 periods of SDRWS, is calculated in details on computer. After calculating S 11 of the input cavity and an output cavity and the eigenmodes of the intermediate cavity, the structural parameters of the input cavity and an output cavity and the intermediate cavity are determined, then PIC simulation is done to predict the ElK's performance, the results show that the EIK has an 1 GHz-wide of 3 dB band which cover 219.5-220.5GHz, a 456 W of maximum power and a 40.06 dB of maximum gain. Furthermore, stagger tuning by adjusting the structural parameter $a$ of the intermediate cavity is performed to analyse how $a$ affects the ElK's performances, and the results show that the 3 dB band of the EIK mainly depends on the passband of the input cavity and an output cavity, but also depends on the resonant frequency of the intermediate cavity in some cases. When the resonant frequency of the intermediate cavity is located at the lower or higher ends of the passband of the input cavity and an output cavity, the 3 dB band of the EIK may be extended to certain extent. Particularly, when the resonant frequency of the intermediate cavity is located at or beyond the higher ends of the passband of the input cavity and an output cavity, it is verified that the EIK has steady output signal featuring with pure spectrum and has flat gains over the 3 dB band. The final results of the stagger tuning show that, when the structural parameter $a$ of the intermediate cavity is 0.747 mm, the EIK reaches almost the optimum performances, with an 1 GHz-wide of 3 dB band which cover 219.5-220.7GHz, a 630 W of maximum power companied with a 11.3% of efficiency, and a 47 dB of maximum gain.