Design and Measurement of a Terahertz Double Staggered Grating Waveguide With an Arc-Shaped Beam Tunnel

A millimeter-waveband double staggered grating waveguide (DSGW) with an arc-shaped beam tunnel was previously proposed for sheet beam traveling wave tubes. In this article, the design, fabrication, and cold test of a terahertz band DSGW with an arc-shaped beam tunnel are presented. Simulations demonstrated that the novel DSGW would have a higher coupling impedance and a better beam wave interaction in comparison to the conventional DSGW with a linear-shaped beam tunnel. Beam wave interaction simulations showed that the output power and the electronic efficiency, respectively, increased from ~420 W to ~580 W and from 7.0% to 9.3% at 240 GHz. These two kinds of DSGWs were fabricated by using the nanocomputer numerical control (CNC) milling and wire cutting techniques, and their performances were cold tested by using a vector network analyzer. The measurement results were in good agreement with the simulations and demonstrated that both the traditional and novel DSGWs achieved a wide frequency bandwidth of ~40 GHz (0.22-0.26 THz) with a transmission coefficient S
₂₁
better than -2.7/-3.0 dB and a reflection coefficient S
₁₁
lower than -13.0/-15.7 dB, respectively.