模拟研究了一种在均匀慢波结构后增加渐变慢波结构段的太赫兹过模表面波振荡器,获得了输出功率和模式纯度的显著提高。首先根据S参数方法,研究分析了这种复合高频结构中TM01模的谐振特性。然后采用2.5维PIC(Particle-in-cell)软件UNIPIC,模拟研究了振荡器输出性能随渐变慢波结构周期数的变化关系。结果表明：随着周期数的增加,输出太赫兹波中的TM02和TM03等高次模成分降低,TM01模的功率比例增大至80%以上；选择合适长度的渐变慢波结构,能使得器件输出功率增大50%。

A terahertz overmoded surface wave oscillator (SWO) with tapered slow wave structures (SWS) added after the uniform SWSs is investigated, and the notable enhancement of output power and mode purity is obtained. At first, the resonant characteristics of the multiple high frequency structure are studied and analyzed by using the S-parameters method. Then a 2.5 dimensional particle-in-cell (PIC) code UNIPIC is employed to simulate and research the variation relations between the output performance of the oscillator and the length of tapered SWSs. The results show that the power ratio of TM01 mode in the output terahertz wave increases to be over 80% with the increase of period number, while ratios of TM02 and TM03 higher modes are suppressed efficiently; and the output power of the oscillator with appropriate length of tapered SWSs is 50% more than that from SWO with uniform SWSs.