An RF Design of Biperiodic Multimode Interaction Circuit for $\textit{G}$ -Band Extended Interaction Klystron

An RF design of biperiodic multimode interaction circuit for G-band extended interaction klystron (EIK) is presented to overcome the bandwidth limitation of conventional EIK operating in a single mode. The p-mode and its adjacent ladder mode are chosen as the operating modes of the input and output cavities. The effect of beam loading and the presence of the waveguide port on the cavity characteristics of the output cavity operating in the multiple modes are investigated, including the coupling coefficients, the frequencies, and the hot quality factors. The bandwidth of the gain section is broadened by the staggered tuning method. The 3-D particle-in-cell (PIC) simulation predicts a constant drive bandwidth of 4.5 GHz (exceeding 2% relative bandwidth) for the designed power amplifier around 220 GHz. Driven by a 21.4-kV, 0.25-A pencil electron beam, the amplifier can provide an output power of 195 W when the input power is 70 mW. The corresponding gain and electronic efficiency are 34.5 dB and 3.6%, respectively.