Study on the Efficiency of Two-Beam Extended Interaction Oscillator toward 200 kW at Ka-band

A compact high-efficiency two-beam extended interaction oscillator (EIO) with an improved ladder structure is proposed to achieve a high output power of 200 kW. The Ka-band continuous wave two-beam EIO with five gaps is designed to operate in the $\mathbf{TM}\mathbf{31}-\mathbf{2}\boldsymbol{\pi}$ mode. The effects of the external quality factor $(\mathbf{Q}_{\mathbf{e}})$ , perveance $(\mathbf{P}_{\mathbf{t}})$ and phase velocity changes in the last period on the efficiency improvement of the EIO are analyzed. The efficiency improvement from 28 % to 41 % is predicted by the 3-D particle-in-cell (PIC) simulations performed in CST. A stable output power of 205 kW and 41% efficiency are obtained at 52 kV and $\mathbf{4.8}\times \mathbf{2}$ A. An effective method for dramatically increasing the efficiency of millimetre-wave EIOs is presented in this paper.