Shenzhen University (2018046).Abstract-The design, fabrication and cold test of a high frequency system (HFS) for an H-band (220-325GHz) sheet beam travelling wave tube (SB-TWT) is presented in this paper. The HFS was composed of a 90-period double-staggered grating waveguide and a pair of identical L-shaped couplers with Bragg reflectors and matching steps. The HFS was manufactured by Nano-CNC machining and its electromagnetic properties were measured by using a vector network analyzer. The measured S-parameters were in good agreement with the simulated ones, which predicted a 3 dB bandwidth of ~47.0 GHz. The maximum value of the measured transmission coefficient S21 was -4.9 dB and the in-band port reflection S11 was around -15.0 dB. Based on the cold testing-based HFS, simulations of the beam wave interaction predicted a stable output power of over 55.1 W in the frequency range of 230-280 GHz. In addition, the instabilities of the beam wave interaction were investigated in the simulation.Index Terms-high frequency system, interaction instability, terahertz wave amplification, sheet beam travelling wave tubes.
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