Demonstration of a High Efficiency and Wide Band 30-W G-Band Continuous Wave Traveling Wave Tube

This study demonstrates the recent progress of a G-band continuous wave traveling wave tube with high output power, wide bandwidth and high efficiency. Measures were taken to improve the tube performance. First, the operating point of the folded waveguide slow wave structure was optimized at <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~\pi $ </tex-math></inline-formula> phase advance to ensure both large bandwidth and proper interaction impedance. Then, the phase velocity tapering technique was utilized to significantly enhance the power within a large bandwidth range. Finally, a three-stage depressed collector was employed to dramatically improve the overall efficiency. The prototype tube was fabricated and tested under continuous wave operation with a beam current of 52 mA and voltage of 18.1 kV. The saturation output power measured is over 30 W in 221.2-223.2 GHz and the maximum power is 31 W with the corresponding efficiency of 16.9%. The tube provides more than 20 W and overall efficiency is above 11% with a bandwidth of 13.4 GHz. The weight and size of the device are 1.8 kg and 285 mm <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times 70$ </tex-math></inline-formula> mm <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times 65$ </tex-math></inline-formula> mm, respectively.