Abstract
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.