Design of Broadband Slow Wave Structure and RF Window for Ka-Band Helix TWT

In this article, the design and simulation of helix slow wave structure (SWS) with dielectric support rods for Ka-band Helix-traveling wave tube (TWT) have been described. The beam-wave interaction analysis and simulation of a small helix structure have been carried out to obtain the wide bandwidth, high gain, and high power of Ka-band TWT. The dispersion and interaction impedance characteristics of helix SWS have been determined using computer simulation tool (CST)-microwave studio and experimentally measured. The design and simulation predict that helix SWS can produce >100 W output power, 55.0 dB saturated gain, 8.0 GHz bandwidth, and 30% efficiency at a 27.5–35.5 GHz frequency range. A new type of waveguide pillbox wideband output RF window has been fabricated and experimented. The stability analysis of the helix SWS also demonstrates that the loss design is a major effective for suppressing the backward oscillations in the helix TWT.