Demonstration of an Ultracompact, High-Isolation Power Coupler for W-Band Sheet Beam Traveling Wave Tubes

Abstract

The emerging sheet beam devices have become a research hotspot in the field of vacuum electronics due to their excellent performance in the millimeter-wave and even terahertz bands, but there are still many technical bottlenecks in the actual manufacture and the engineering realization. In this article, an ultracompact high-isolation power coupler prototype is demonstrated for high-efficiency injection and extraction of electromagnetic energy from the sheet beam traveling wave tubes (SB-TWTs). The introduction of polarized rotators avoids the coupling of electromagnetic waves into the electron channel, thereby improving isolation performance. The improved structure with multiparameter tunability ensures low reflection and broadband characteristics. The simulation shows that its extreme bandwidth (BW) is 40% and the in-band isolation is less than −50 dB. Moreover, the parasitic resonance mode is analyzed and related suppression technology is also proposed. Then, two prototypes of a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${W}$ </tex-math></inline-formula> -band coupler have been processed and tested. The related machining errors have been analyzed and a good consistency is verified between the experiment and the simulation. Compared with the best level of the existing coupler, this ultracompact structure with less than one free-space wavelength (calculated from the central frequency point) relieves the pressure of the sheet beam transmission system, reduces the risk of electronic interception, and provides a feasible solution for engineering realization of sub-millimeter-wave or terahertz SB-TWTs.