A Novel Rectangular Groove Sine Waveguide Slow Wave Structure for Millimeter-Wave TWT

A novel slow wave structure (SWS) called the rectangular groove sine waveguide (RGSWG) SWS is proposed. The proposed structure incorporates a rectangular groove inside the sine waveguide (SWG), which runs parallel to the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$H$</tex-math> </inline-formula>-plane of the waveguide. The high-frequency characteristics of this innovative SWS have been simulated. The calculations reveal that the average impedance of the RGSWG SWS is approximately twice that of the conventional SWG SWS. In addition, high-frequency transmission systems for both the RGSWG and the conventional SWG have been designed and analyzed. The results demonstrate that the RGSWG slow wave circuit exhibits superior reflection characteristics. The beam–wave interaction of RGSWG traveling-wave tube (TWT) was analyzed using particle simulation software. In the operating frequency range from 90 to 98 GHz, the RGSWG TWT can produce an output power of over 52 W, given an input power of 150 mW, an operating voltage of 9.3 kV, and a beam current of 200 mA. This RGSWG TWT attains a maximum output power of 77 W at the typical frequency of 94 GHz, with a corresponding gain of 27.1 dB. In comparison, under the same conditions, the conventional SWG TWT can only produce an output power of 36 W in the operating frequency range of 90–98 GHz. The RGSWG has been fabricated and tested, with the test results largely consistent with the calculated outcomes. The test results indicate that the insertion loss is greater than −3.4 dB within the frequency range of 89–100 GHz, and the return loss is below −15 dB.