Investigation of a Low-Loss Transmission Structure for W-Band TWT

A low-loss transmission structure for W-band traveling wave tube (TWT) is proposed in this article. It converts the rectangular waveguide fundamental TE10 mode into the corrugate waveguide HE11 mode with a quasi-Gaussian energy distribution, thereby reducing ohmic loss on the waveguide walls. The sections maintaining and generating the HE11 mode are theoretically analyzed. The simulation results show that the ${S} _{{11}}$ of the converter is less than −20 dB in the frequency range of 80–100 GHz, and the mode conversion purity reaches 99.66%. Compared with a conventional rectangular waveguide with a 4.5 dB/m transmission loss, the insertion loss of novel structure has successfully been reduced by 3.1 dB/m to as low as 1.4 dB/m Furthermore, the same length W-band low-loss transmission structure and rectangular waveguide have been fabricated and cold-tested, the results reveal a reduction in insertion loss of 2.5 dB per meter, verifying the simulation predictions. A burned spot experiment was conducted to verify the energy distribution of the HE11 mode. The experimental results confirm the feasibility of the proposed low-loss transmission structure for low-loss transmission in W-band TWT input-output structures.