Experimental Characterization of Dispersion and Phase Velocity in a Miniaturized Double-V Meander-Line Slow-Wave Structure

Abstract

A very-low-voltage double V-shaped meander-line slow-wave structure (ML-SWS) for miniaturized traveling-wave tubes (TWTs) is presented and experimentally characterized. The proposed topology enables strong beam–wave interaction at cathode voltages below 2 kV while maintaining compact dimensions and full compatibility with planar microfabrication processes. The structure is designed to operate over the 17–21-GHz frequency range and to provide a nearly constant phase velocity suitable for low-voltage electron beams. A prototype composed of 40 unit cells was fabricated on an alumina substrate and characterized through cold-test measurements. The dispersion diagram and phase velocity were extracted from the measured phase of the S21 parameter and compared with eigenmode and time-domain simulations, showing good agreement with discrepancies below 10%. Particle-in-cell simulations were subsequently carried out to evaluate the hot-test performance. At a cathode voltage of 1.425 kV and a beam current of 100 mA, the structure achieves a maximum gain of 34.1 dB and a peak beam–wave electronic efficiency of 18% at 18 GHz. With a slow-wave structure (SWS) volume of only 0.203 cm3, the proposed double V-shaped meander-line (ML)-SWS demonstrates high power density and represents a promising solution for compact, low-voltage TWTs intended for aerospace and space applications.