Asymmetric Mode Competition Excitation and Suppression in a Triple-Band Frequency-Agile High-Power Microwave Oscillator

Abstract

Mutual interference and high overmoded ratios in multiband frequency-agile high-power microwave (FA-HPM) oscillators readily induce asymmetric mode competition, severely degrading the output power and pulsewidth in experiments. Traditional asymmetric mode competition suppression methods are designed for single-frequency HPM oscillators, making them inadequate for ensuring operating stability across multiple frequencies in FA-HPM oscillators and prone to introducing new asymmetric mode competition. To address this challenge, this article proposes a novel asymmetric mode competition suppression method for multiband FA-HPM oscillators. This method relies on a “locate-analyze-optimize” mechanism to suppress the asymmetric mode competition induced by the TM₁₁₂ and TM₂₁₂ modes under Ku-band operation, as well as the EH₃₁ mode under X-band operation in the triple-band FA-HPM oscillator. It identifies the excitation region of asymmetric modes through temporal evolution analysis of the electron beam’s kinetic energy, revealing that a high external quality factor ( $Q_{e}$ ) and high reflection characteristics are the key factors contributing to the excitation and growth of asymmetric modes. Ultimately, the excitation of asymmetric modes is effectively suppressed by increasing the gap width of the high-frequency structures. Under actual voltage waveform conditions, no asymmetric mode competition occurs in this device. In addition, this method can be applied to resolve asymmetric mode competition issues in various O-type high-power microwave oscillators.