Investigation of Rods Shapes and Materials Influence on Q-Band Travelling Wave Tube High Frequency Characteristics

This investigation aimed to find a compromise between enough heat dissipation, high interactive impedance and low RF loss. Several constructions of helix slow-wave structure (SWS) with different dielectric rods shapes (i.e., rectangular, wedge, T-shaped, and stairs) are analyzed in this paper. The use of the promising SWS construction with stairs-shaped dielectric rods allowed to obtain 47% increase in interactive impedance value compared to the initial SWS with rectangular BeO rods. Scrutiny of two rods materials (beryllium oxide and boron nitride) revealed that use of the latter one and three times reduction of rods width lead to 94 % increase in interactive impedance value compared to the first calculated SWS with thick BeO rods. Conducted wire geometry optimization provided minimum level of RF loss and sufficient heat dissipation. Calculations of interactive space construction confirmed the benefit of using SWS construction with BN rods: 6-8% increase in output power was obtained within operating range.