Demonstration of W-Band 30-W Continuous-Wave Folded Waveguide Traveling Wave Tube with Lowered Operation Voltage and Improved Gain Flatness

We have demonstrated and developed a W-band 30 W continuous-wave folded waveguide traveling wave tube (CW FWTWT) with 13.5-kV operation voltage and 4.8 dB gain flatness. In this paper, we quantitatively study the relationship between operating voltage and the key geometric dimensions of a folded waveguide, which is the key to the design of the low-voltage TWT. In addition, problems of improving beam transmission and suppressing oscillations are also studied, and the related design methodologies of the long-range electron gun, periodic permanent magnet (PPM) focusing system, low-voltage standing wave ratio (VSWR) coupling system, and horseshoe attenuator are discussed. On the basis of the above analysis, we have designed and fabricated two types of W-band CW TWTs. The test results show that beam transmissions are over 98.5% at DC and better than 96.5% at the highest peak RF power. Measured saturated output powers are greater than 33.6 W with saturated gain more than 42.2 dB within frequency range of 91-99 GHz, and an improved gain flatness of 4.8 dB is achieved.