Simulation of folded waveguide slow wave structure with grooves for W-band TWTs

Abstract

Folded Waveguide Slow Wave Structure (FW SWS) is a promising structure for millimeter wave travelling wave tubes (TWTs) due to its moderate band width, high power handling capability, reliability and its ease of fabrication. FW SWS with groove is used to improve interaction between RF wave and electron beam by introducing grooves in the conventional FW SWS. In this paper, design of a folded waveguide slow wave structure with rectangular groove has been carried out using the 3D electromagnetic software package CST Microwave studio at W-band and at 19 kV beam voltage. FW SWS rectangular groove increases interaction impedance by 15.48% as compared to the conventional serpentine FW SWS. However, the cold bandwidth of the FW SWS with groove is reduced by 15.29% as compared to the conventional FW SWS. The length and width of the rectangular groove can be adjusted to either increase or decrease the interaction impedance or bandwidth. PIC simulation has been done for FW SWS with rectangular groove and it gives 23.30 dB gain.