A Modified Fold Waveguide Slow Wave Structure for W-Band Dual-Beam TWT

Increasing the interaction current capacity and the interaction impedance is crucial to achieving high output power for traveling wave tubes (TWTs) in ${W}$ -band and terahertz (THz)-band. With the increased distance between the upper and lower metal walls of folded waveguide (FW), the slow wave structure (SWS) named dual-tunnel FW (DTFW) is formed. Benefiting from such a rational design, the electric field in the noninteracting region decreased and naturally formed dual electron beam tunnels. Meanwhile, the operating mode is cutoff at the beam tunnel, the electromagnetic wave in DTFW can be propagated along the path similar to FW and operate in the fundamental mode. Furthermore, compared with FW, due to its larger size, the DTFW has the same structural complexity and less manufacturing difficulty, which is significant for ${W}$ -band and THz-band. In this article, through the analysis of the high-frequency characteristics of the SWS using FW and DTFW, the physical mechanism of bandwidth and interaction impedance improvement of DTFW-SWS are revealed. Moreover, the particle-in-cell (PIC) simulation results reveal that, compared with a TWT using unprecedentedly excellent FW-SWS, the performance of TWT using DTFW-SWS has been significantly further improved in the aspects of saturated power, gain, and electron efficiency. Therefore, DTFW-SWS is a promising SWS for high-power and wide-bandwidth TWT in ${W}$ -band and THz-band.