Design and measurement of high Q-factor coaxial resonant cavity
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摘要: 随着高功率微波源向高功率、高频率和长脉冲方向不断发展，同轴相对论速调管放大器（RKA）成为近年来研究热点之一，然而其发展一直受限于自激振荡等问题存在，为此，设计一种高Q值单间隙同轴谐振腔，以抑制同轴RKA中TEM模式泄露引起的自激振荡。通过对单间隙同轴谐振腔TM01模式与TEM模式转化进行理论分析与仿真模拟，发现同轴谐振腔上下槽深差值与轴向错位值对其Q值变化影响很大，当上下槽深差值与轴向错位值分别为0.3 mm和0 mm时，同轴谐振腔的Q值为极大值（18 764），意味着此时谐振腔中两种模式转化最小，多组谐振腔级联后自激振荡风险大大降低。将三组级联的高Q值单间隙同轴谐振腔应用于紧凑型同轴RKA，粒子模拟和实验结果表明，器件的输出微波功率稳定，频谱纯净，无自激振荡等问题存在。
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关键词:
- 同轴相对论速调管放大器 /
- 自激振荡 /
- 高Q值 /
- 单间隙同轴谐振腔
Abstract: With the development of high power microwave sources towards high power, high frequency and long pulse, coaxial relativistic klystron amplifiers (RKA) have become one of the research hotspots in recent years. However, its development is limited by self-excited oscillation, etc. Therefore, a high Q-factor single-gap coaxial resonator is designed in this paper to suppress the self-oscillation caused by TEM mode leakage of the coaxial RKA. Through the theoretical analysis and simulation of TM01 mode and TEM mode conversion in a single-gap coaxial resonator, it is found that the depth difference and axial dislocated values of the upper and lower slots of the coaxial resonator have a great influence on the change of its Q factors. When the depth difference and axial dislocation value of the upper and lower slots are 0.3 mm and 0 mm respectively, the Q factor of the coaxial resonator has the maximum value (18 764). This means that the conversion between the two modes in the resonator is minimal, greatly reducing the risk of self-oscillation between several cascaded coaxial resonators. When three cascaded high-Q-factor single-gap coaxial resonators are applied to the compact coaxial RKA, the output microwave power of the device is stable, the spectrum is pure, and there are no self-excited oscillations in the simulation and experiments. -
图 3 同轴谐振腔中TEM和TM01模式电场和磁场分布
Figure 3. Radial electric and magnetic field field distributions of TEM and TM01 modes in the coaxial resonant cavity
图 4 同轴谐振腔I区和II区的电场和磁场分布
Figure 4. Electric and magnetic field distributions in I and II zones of a coaxial resonant cavity
图 6 同轴谐振腔Q值随内外槽深差值Δr变化
Figure 6. Simulated Q-factor values of a single-gap coaxial resonant cavity versus Δr
图 7 同轴谐振腔Q值随内外错位值Δl变化
Figure 7. Simulated frequency and Q-factor values of a single-gap coaxial resonant cavity versus Δl
图 9 同轴相对论RKA中不同Q值对应的基波调制电流深度
Figure 9. First harmonic current ratios in the coaxial RKA with different Q factors
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