Experimental investigation of millimeter wave folded-waveguide TWT

Folded-waveguide traveling-wave tube (FWTWT) is one of the candidates for high power, broad-band robust millimeter wave sources. The FWTWT has no periodic reactive load. Therefore, the dispersion relation of space harmonics is estimated by simple transform of that of rectangular waveguide. The folded waveguide circuits are designed and fabricated using 12 kV, 150 mA linear electron beam for Ka-band amplifier and oscillator based on the synthesis process. Solenoid focusing system and pulsed electron beam are used to investigate basic properties of FWTWT in the laboratory. Non-stationary beam-wave interactions performance are investigated by MAGIC3D, and one-dimensional code. From initial folded-waveguide BWO experiment, about 20-watt output power at 35 GHz is obtained with 6% linear tunability. The LIGA fabrication is in process for the operation at the higher frequency.