Design and Analysis of an Overmoded Circuit for Two-Beam Sub-THz Extended Interaction Oscillator

An effective overmoded circuit is proposed to support efficient interaction with two beams for the development of high power extended interaction oscillators (EIOs) toward sub-terahertz (THz) and higher frequency. The circuit design focuses on the effect of the frequency-determining parameter on mode characteristics of the $\mathrm{TM}_{{1} {n}}$ sequence. Frequency equivalence between $\mathrm{TM}_{{1} {n}}$ modes with different ${n}$ supports the mode selection for two-beam interaction. Accordingly, the TM13 mode is selected to duplicate the dispersion relation around the axial mode of $2\pi $ and ohmic loss of conventional TM11 mode used in conventional single-beam circuits. On this basis, the overmoded circuit is formed with two beams based on the TM13 mode. In order to verify its effectiveness, a 0.22-THz EIO is designed with the overmoded circuit and, most importantly, the effect of the uniformity of two beams on the EIO performance is simulated. When the current of one beam is assumed to be constant and that of another beam is increased, the power is increased linearly and then tends to be saturation. This shows good capability of the EIO in interacting with nonuniform two beams, which is critical for its stable operation. Simulation results have shown the achievement of the average power of 0.22-THz wave over 1.26 kW with double beams at 23 kV and each current of 0.2 A.