虛陰極振盪器具有結構簡單、高微波峰值功率、電子束品質要求低且不需外加磁場等特殊優點，因而容易發展成為體積小、重量輕、可靠度高的緊湊型高功率微波源。但是窄脈寬(<100 ns)、頻率飄移、輸出功率不穩定與相對低的電子束-微波的能量轉換效率(束-波轉換效率< 3 %)乃是虛陰極振盪器的主要缺點。因此本文提出了”軸向共振腔式陰極環翼虛陰極振盪器”，一種於軸向式虛陰極振盪器的陰極上增加外環翼翅(cathode wing)，並在陽極網後端外加一開口式共振腔(open cavity)的方法來改進上述虛陰極振盪器的缺點，並經由實驗獲得驗證，得到脈寬高達120 ns、頻率與模式單純、輸出功率大於200 MW的微波峰值功率，且束-波轉換效率高達4.5 %以上。此外由於超窄脈寬與雜亂頻譜使得精準地量測虛陰極振盪器的輸出功率一直都是件困難的工作，這裡我們提出一個解決方案，透過時間頻域分析法(Time-Frequency Analysis)來分析虛陰極振盪器的輸出訊號，因而從實驗結果得到準確的輸出功率。

The virtual cathode oscillator (vircator) is a widely investigated device for the generation of very high-power microwaves (HPM). Because of its structural simplicity, frequency tuneablity, the allowance of rather poor electron beam quality and no need of external magnetic field, vircator has become the most readily available compact HPM sources. However, there are some drawbacks of vircator such as short pulse length (less than 100 ns), low-power conversion efficiency (less than 3 %) and non-coherent radiation. In this dissertation, an axial vircator with cathode wing and an open cavity in the back of anode mesh is presented to overcome those drawbacks. Experimental results show that the axial vircator with cathode wing and cavity obtains pulse duration of 120 ns, pure frequency, single mode, higher than 200 MW output power and conversion efficiency above 4.5 %. Precise measurement of the power generated by a virtual cathode oscillator has been a difficult task because of the ultra short duration of the microwave pulse and the complexity of its frequency spectrum. Here, we report a resolution to this problem through the Time-Frequency Analysis of the output signal and thereby an accurate determination of the output power from the experimental data can be obtained.

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