Design of a Helix SWS with Coupler for Compact Ka-band Space TWT

Travelling Wave Tubes (TWTs) are essential in satellite communications and radar systems for amplifying high-frequency signals. While different slow-wave structures were explored in the past, the helix continues to be the preferred option for achieving broad bandwidth. The helix TWT stands out with exceptional performance, primarily due to its unique combination of compact size, lightweight design, high efficiency, strong linearity, significant output power, and wide bandwidth. Here, a design of helical slow wave structure (SWS) and input/output couplers operating in the Ka-band (20 to 22 GHz) frequency range have been presented, particularly for a compact space TWT. Initially, the geometrical parameters of a single-turn helix have been optimized by studying its dispersion characteristics and interaction impedance in the desired band of tube operation. Then, the multi-turn helical SWS length has been optimized to achieve high electronic efficiency and high gain of the space TWT. The design of the input and output couplers has been analyzed using S-parameters and optimized for high coupling efficiency. The design of the helical SWS and couplers has been optimized specifically for compact Ka-band space TWTs, with a strong emphasis on achieving high electronic and circuit efficiency, making it valuable for space TWT designers.