Design and Cold Test of a Broadly Tunable Terahertz Short Double-Grating Rectangular Waveguide Slow Wave Structure

A short double-grating rectangular waveguide (DGRW) slow wave structure (SWS) is designed and compared in detail with DGRW. Significant modifications are made to the corrugation geometry to optimize the dispersion characteristics, resulting in a broader frequency passband and enhanced frequency tunability. The high-frequency performance is analyzed in terms of dispersion and interaction impedance. The structure shows an interaction impedance of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1.5~\Omega $ </tex-math></inline-formula> at 0.34 THz. To confirm the effectiveness of the proposed design, a 0.34-THz backward wave oscillator circuit is designed and fabricated comprising 160 periods. The circuit is assembled and cold-tested for scattering parameters. The results show <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${S}_{{21}}$ </tex-math></inline-formula> values above −1.5 dB and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${S}_{{11}}$ </tex-math></inline-formula> below −20 dB for a broad frequency range. The beam-wave interaction simulations using a 30-kV, 30-mA electron beam, and 0.2-T focusing magnetic field show that the backward wave oscillator based on the proposed design achieves an average output power of 16 W at 0.34 THz, with a frequency tuning range of 95 GHz when compared with 57 GHz for the DGRW-based backward wave oscillator.