RF Design of a Novel Interaction Circuit for 0.23-THz EIK

In this article, a novel single-mode extended interaction klystron (EIK) operating at 0.23 THz with the isosceles trapezoidal neck resonant cavities is proposed and analyzed. Compared with the conventional ladder-type structure, the use of this isosceles trapezoidal neck structure further strengthens the axial electric field in the tunnel of the beam of the resonant cavity and enhances the strength of the beam–wave interaction. In addition, it is demonstrated for the first time that the trapezoidal neck cavity can increase the transmission bandwidth, which is favorable for the bandwidth extension of the EIK. By investigating the high-frequency characteristics as well as the beam–wave interaction, a six-cavity, five-gap TM <tex-math notation="LaTeX">₃₁</tex-math> single-mode EIK is constructed. After stagger tuning, the 3-D particle-in-cell (PIC) simulation predicts that the designed multicavity EIK produces the stable 176.4 W of output power from a 20-mW input driving signal, with a gain of 39.45 dB, an efficiency of 3.89%, and a 3-dB operating bandwidth of 1.14 GHz at 230.56 GHz. These results demonstrate certain superiorities of this structure in terms of performance improvement of terahertz single-mode EIK.