Dispersion of the Multimode Circuit Designed for the Extended Interaction Devices

A newly proposed multimode circuit designed for extended interaction devices (EIDs) has demonstrated its ability to achieve multimode oscillation and multimode amplification in the millimeter-wave bands. Various distinctive features related to this multimode circuit, especially its discontinuous dispersion, have been observed. Herein, the dispersion characteristics of this multimode circuit are comprehensively studied. The dispersion is verified through theoretical analyses, simulation, and cold test; S-parameters, the “break” in the dispersion, and the high-order modes are analyzed. This study lays a scientific foundation for the multimode working mechanism and offers guidance for the optimal design of the multimode circuit. It can also be applied to the research of conventional extended interaction circuits and enlightens other potential multimode circuits designed for high-efficiency broadband electron beam-driven terahertz sources.