Compact E-Band Sheet Beam Folded Waveguide Traveling Wave Tube for High Data Rate Communication

Abstract

The design of a compact <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\textit{E}$</tex-math> </inline-formula> -band (71–76 GHz) sheet beam (SB) folded waveguide (FWG) traveling wave tube (TWT) for high data rate communications is presented in this article. The round beam tunnel for a pencil FWG slow wave structure (SWS) has been redesigned with a rectangular beam tunnel to be suitable for the SB with increased beam current. A novel periodic permanent magnet (PPM)–periodic quadrupolar magnet (PQM) focusing system has been developed to reduce the beam ripple and improve the transmission ratio. A multistep side-out coupler is designed to import and extract the RF power from the SWSs and be compatible with the planar periodic magnetic focusing system. Particle-in-cell (PIC) simulations are employed to evaluate the performance of the high-frequency circuit. Driven by a 1 W signal, the 30-period circuit is estimated to produce more than 100 W power and achieve a 21 dB gain with a less than 0.4 dB variation over 71–76 GHz. Moreover, phase and linearity analysis show a less than 6 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^{\circ}$</tex-math> </inline-formula> in-band phase distortion and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\sim$</tex-math> </inline-formula> 30 dB third-order intermodulation distortion (C/3IM) at 30 W of output power, meeting the requirements of a communications-focused TWT. Over 5% circuit efficiency and 40% overall efficiency when equipped with a single-stage collector can be achieved by the compact TWT over the target band.