Research on a High-Order Mode Multibeam Extended-Interaction Oscillator With Coaxial Structure

The stable operation of the high-order mode multibeam extended-interaction oscillator (EIO) with coaxial structure can effectively overcome the size limitation of the fundamental mode operating circuit at high frequency. The research on the transverse mode shows that the high-order TM31 mode can establish a stronger axial electric field than the fundamental TM01 mode in a large size coaxial cavity. Although the design of a coaxial extended interaction cavity is straightforward, the operating stability is greatly affected by the mode competition. Based on the interaction characteristic between the multiple beams and the multigap cavity operating in the high-order mode, this article proposes a simplified analysis method based on the equivalent circuit theory to study the high-frequency characteristics of the complex structure. The space-charge wave theory is combined with the dispersion curve to analyze the stability of the five-gap coaxial EIO operating in the TM31 mode. Finally, the particle-in-cell (PIC) simulation has obtained a TM31 mode EIO operating at 35.3 GHz with an output power of 290.3 kW. The device uses six beams with a total current of 25.8 A (evenly divided among six beams) at a voltage of 51 kV. The design provides a promising approach for making a stable high-power RF circuit applied in high-frequency EIOs.