HIGH EFFICIENCY AND HIGH POWER STAGGERED DOUBLE VANE TWT AMPLIFIER ENHANCED BY VELOCITY-TAPER DESIGN

Previously reported staggered double vane (SDV) slow wave structure (SWS) traveling wave tube (TWT) gave electron efficiency as low as 3.4% at 220 GHz, which needs to be improved. One easy method to improve the electron efficiency and the output power is to reuse the spent electron beam energy, by resynchronizing electron velocity to the phase velocity of the terahertz (THz) signal at the second section of the TWT. In this article, we have modified the pitch of the SWS to realize the tapered phase velocity, which is for the first time, to our knowledge, applied to the SDV SWS at 220 GHz. By varying the geometry configuration, an optimized structure of tapered pitch SWS has been successfully developed. The results reported in this paper show a significant improvement of the output power, gain and electron efficiency. At 220 GHz, the output power has increased by about 65% with respect to the previous reported value reaching 111 W, and the electron efficiency has improved from 3.4% to 5.6%. In order to simplify the microfabrication process, an input/output coupler with E-plane bending has been designed, which can be fabricated by using only one mask UV-LIGA process.