Investigation of a Low-Loss Transmission Structure for <i>W</i>-Band TWT

A low-loss transmission structure for <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">W</i>-band traveling wave tube (TWT) is proposed in this article. It converts the rectangular waveguide fundamental TE<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><roman>10</roman></sub> mode into the corrugate waveguide HE<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><roman>11</roman></sub> mode with a quasi-Gaussian energy distribution, thereby reducing ohmic loss on the waveguide walls. The sections maintaining and generating the HE<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><roman>11</roman></sub> mode are theoretically analyzed. The simulation results show that the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">S</i><sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><roman>11</roman></sub> 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 <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">W</i>-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 HE<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><roman>11</roman></sub> mode. The experimental results confirm the feasibility of the proposed low-loss transmission structure for low-loss transmission in <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">W</i>-band TWT input–output structures.