| High-power coaxial virtual cathode oscillator (vircator) has been investigated as a high-power microwave source for over twenty years. To improve its power efficiency from ∼5% to ∼10%, we need more theoretical understanding in microwave generation mechanisms of the coaxial vircator. Although the axial vircator has been studied in depth, some mechanisms in the coaxial vircator are still unknown.; In this dissertation, several attempts are made to understand the microwave frequency and propagating mode determination mechanism in a coaxial vircator. A new formula is introduced to revaluate the space-charge limited current density, which relates to virtual cathode oscillation frequency. A concept, virtual cavity, is introduced to explain a physical phenomenon in microwave generation. Experimentally, some efforts are made to measure the microwave propagating modes in a circular waveguide. The identification of the propagating modes is helpful in microwave power evaluation and resonance effect research. |
