Analysis of a New Metamaterial-Loaded Helical Slow-Wave Structure for Vacuum Electron Device Applications

The design of a metamaterial-loaded helical slow-wave structure (MHSWS) is proposed, facilitating the dual purpose of enabling forward-wave (FW) propagation for traveling-wave tubes (TWTs) at lower frequencies and backward-wave (BW) propagation for BW oscillators at higher frequencies within the propagation band. A practically feasible interaction structure is designed, and its dispersion and interaction characteristics are analyzed using CST microwave studio (CST-MWS). An in-depth electromagnetic (EM) field analysis of the proposed MHSWS is conducted, deriving dispersion and interaction impedance formulas to analyze its propagation characteristics comprehensively. Comparative analyses between theoretical and simulation results ensured the reliability of numerical characterizations for the structure, highlighting a strong agreement between theoretical and simulation outcomes. The designed MHSWS supported both FW and BW modes, along with the point of mode-degeneracy that facilitates the slowing and stopping of EM waves inside the structure. Leveraging its advanced propagation and interaction characteristics, the proposed MHSWS established its applicability to designing high-efficiency interaction circuits for vacuum electron device applications.