Experiments of Sub-THz Wave Folded Waveguide Traveling-Wave Tube Amplifier

This study showed the possibility of using a sub-terahertz (THz) traveling-wave tube (TWT) via measuring the transmission characteristics and TWT performance of the circuit by applying X-ray LIGA, a micro-fabrication process, to the interaction circuit. The applied circuit type, an E-bend folded waveguide, is a simple structure most suitable for lithography. A total of three applied frequencies were used the W-band, G-band, and 850 GHz. Among the manufactured circuits, the W-band circuit was applied to the TWT, one of the vacuum electronics devices (VEDs). This was done to prove the manufacturing accuracy of the circuit by comparing the nonlinear characteristics of the circuit with the prediction results. Through such testing, the small signal gain was measured as 13 ± 2 dB under the conditions of 13.96-kV and 24.2-mA electron beam energy. The frequency bandwidth was extremely wide, about 9 GHz, and showed similar characteristics to the simulation predictions. The maximum output of the device was obtained up to 1 W or more at 87.12 GHz by slightly increasing the beam current. These characteristic achievements showed the suitability of the TWT for very small circuits fabricated using the X-ray LIGA process, further suggesting the applicability of other sub-THz bands.