Study of a cascaded amplifier circuit for G -band extended interaction klystron

A cascaded amplifier circuit (CAC) for extended interaction klystron (EIK) is proposed to meet the growing demand for compact millimeter-wave sources. Each EIK stage acts as a subsystem of the cascaded amplifier. Step-by-step amplification is achieved by coupling the amplified signal from the output cavity of the preceding stage into the input cavity of the subsequent stage. By employing a voltage-gradient design in which the subsequent stage operates at a higher voltage than the preceding stage, a stronger longitudinal modulation response is achieved, thereby reducing sensitivity to fluctuations induced by adverse effects in the preceding stage and enhancing the fault tolerance and system robustness under multi-stage cascaded operation. The cascaded amplifier achieves stronger beam modulation over a relatively short interaction length while maintaining bandwidth, thereby reducing the requirement for focusing magnetic fields. Results suggest that the CAC composed of two EIK stages can deliver an output power of 254 W at 220.2 GHz, with a gain of 44 dB and a 3 dB bandwidth of 1.3 GHz. Stability evaluation of the circuit indicates that performance fluctuations caused by electron beam dispersion in the preceding stage are less significant than those in the subsequent stage, thereby alleviating the accumulation of adverse effects, which is critical for achieving device integration.