Study of a 0.34-THz Ladder-Type Extended Interaction Klystron With Narrow Coupling Cavities

A narrow coupling ladder-type extended interaction klystron (EIK) operating at 0.34 THz is proposed and analyzed. Compared with the traditional THz EIKs, the narrow coupling EIK can offer higher power capability and increased efficiency because such arrangement has higher characteristic impedance and a more uniform electric field in the beam tunnel. This article studies the electric field distribution of the narrow coupling circuits and traditional circuits. Moreover, the coefficient of variation is introduced to quantify the uniformity of the axial electric field in the beam tunnel. The operating stability is also ensured by adjusting the period length and number of cells. The 3-D particle-in-cell (PIC) simulation predicts the ideal EIK, driven by a 0.15-A, 17.5-kV electron beam confined in a 0.22-mm diameter beam tunnel, and generates an output power of 41 W. The corresponding gain, electronic efficiency, and 3-dB bandwidth are 28.03 dB, 1.56%, and 600 MHz, respectively. Finally, in order to verify the feasibility of the designed structure, we perform a sensitivity study on the EIK design for an eight-micron fabrication tolerance assuming normal distributions for all critical dimensions per each cell with PIC simulations.