Tapering Vertical Dimension Technique for the Quasi-periodic Folded-Waveguide TWT to Improve the Bandwidth and Efficiency

A tapering vertical dimension technique (TVDT) is proposed for the quasi-periodic folded-waveguide traveling wave tube (FW-TWT) to improve the bandwidth and efficiency. The dispersion characteristics for the concentric arc FW-TWT with the TVDT are analyzed and discussed. When the power of input signal is set as 1 W and the initial beam voltage (current) is set as 4900 V (0.15 A), the peak output power of the proposed FW-TWT with the TVDT can reach 100.9 W at 88 GHz. Accordingly, the corresponding peak electron efficiency is 13.7%. Furthermore, the 3-dB bandwidth (fractional bandwidth) can reach 17 GHz (18.78%) from 82 to 99 GHz, where the output signal is steady and the corresponding frequency spectrum is quite clean. In addition, the performance of the concentric arc FW-TWT with the TVDT is also compared with that of the other quasi-periodic FW-TWTs.