A Novel Design of G-Band Broadband Low-Gain Fluctuation Slow-Wave Structure With Improved Folded Waveguides

The design method for ultrawideband amplification with low-gain fluctuation is explored for the terahertz folded-waveguide traveling-wave tube (TWT). Although the folded-waveguide circuit has a large cold bandwidth (similar to 30%), effective amplification with a flat gain characteristic can only be achieved in a limited range due to sharply reduced interaction impedance. The situation further deteriorates in the design of a terahertz TWT where an oversized beam tunnel has to be used to facilitate the transport of the beam. Through careful analysis of the folded-waveguide (FWG) design characteristics, a modification to the geometry of the circuit has been proposed, leading to a significant enhancement in design capability. As a result, the interaction impedance is increased by 26% over a wide operation frequency band in comparison to the normal folded-waveguide circuit. This makes it possible to use the phase velocity tapering technology to increase efficiency and balance the gain at the same time. A design example in G-band is presented. The interaction circuit is capable of producing 18-W output power over 30 GHz from 202 to 232 GHz with a gain fluctuation of less than 1.5 dB.

Automated summary

This study explores the design method for ultrawideband amplification with low-gain fluctuation in the terahertz folded-waveguide traveling-wave tube (TWT). Due to sharply reduced interaction impedance, effective amplification with a flat gain characteristic can only be achieved in a limited range in the folded-waveguide circuit. The use of an oversized beam tunnel in the design of a terahertz TWT further worsens the situation. By modifying the geometry of the circuit based on careful analysis of the folded-waveguide design characteristics, the interaction impedance is increased by 26% over a wide operation frequency band, enabling the use of phase velocity tapering technology to increase efficiency and balance the gain. A design example in G-band demonstrates the capability of the interaction circuit to produce 18-W output power over 30 GHz from 202 to 232 GHz with a gain fluctuation of less than 1.5 dB.