A Novel Quadruple Corrugated Waveguide Slow-Wave Structure for Terahertz Applications

A novel quadruple corrugated waveguide slow-wave structure for terahertz radiation sources has been proposed, designed for pencil and sheet electron beams. It is compared in detail with a double corrugated waveguide slow-wave structure in terms of dispersion, interaction impedance, and output power. High-frequency characteristics show 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">$0.77~\Omega $ </tex-math></inline-formula> for quadruple corrugated waveguide sheet electron beam tunnel, <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.55~\Omega $ </tex-math></inline-formula> for quadruple corrugated waveguide pencil electron beam tunnel, and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.5~\Omega $ </tex-math></inline-formula> for double corrugated waveguide at 0.34 THz. To validate the proposed slow-wave structure, a 0.34 THz backward wave oscillator is designed, with a sheet electron beam producing 6.3 W peak power and frequency tunability from 0.281-0.368 THz, and a pencil beam generating 2.6 W peak power with frequency tunability from 0.286-0.365 THz. The double corrugated waveguide-based BWO shows an output power of 2.2 W. 160 periods of the quadruple corrugated waveguide slow-wave structure are fabricated using a computer numerical control milling machine. Cold test experiments 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> above -2 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 -16 dB at 0.34 THz.