Wide band high gain modified-folded-wave-guide slow wave structure for millimeter-wave traveling wave tube amplifier in 6G and beyond back-haul communications

Abstract Millimeter-wave technology is crucial in telecommunications as it enables higher bandwidths and faster data transfer. V-band represents frequencies ranging from 50 to 75 GHz and is used for short-range back-haul communication, defense radar, inter-satellite communications, and space debris detection. Folded waveguide slow-wave structures (FWG-SWS) are an excellent choice for V-band amplifiers due to their wide bandwidths, large gain, and ease of fabrication using modern lithographic processes. This article presents a modified folded waveguide slow-wave structure (MFW-SWS) for V-band traveling wave tube amplifiers (TWTAs) desirable for multi-gigabit 6G and beyond back-haul communications. The MFW slow-wave structure is an FWG-SWS variant that supports an increased RF phase velocity, accommodating additional SWS length for much-improved amplification. The dispersion analysis effectively provides a 15% operational bandwidth ranging from 64–74 GHz with a reduced phase velocity of three-tenths the speed of light apt for enhanced beam-wave interactions. The two-section SWS has independent attenuators designed to provide over 20 dB attenuation throughout the functional bandwidth effortlessly. Additional wave-guide transitions are introduced to achieve the best attenuation characteristics. Along the axis of the SWS, a square beam tunnel is employed to support a 26 kV round electron beam with a beam current of 70 mA. To contain the electron beam within the beam tunnel, this study used a focusing mechanism with a constant magnetic field of 0.25T, which is highly appropriate for miniaturization and large-scale implementation in 6G back-haul towers. Particle-in-cell (PIC) simulations were performed using the CST (Computer Simulation Technology) Studio Suite, and a gain of over 26 dB with an output power of 50 W was successfully attained across the operational bandwidth.