Time-Frequency Analysis

Time-frequency analysis has been carried out for microwave radiation from a virtual-cathode oscillator. The ob- jective is to observe and understand the frequency behavior of virtual-cathode oscillation. The diagnostic results have given clear evidence of mode hopping and frequency shifting. The dependence of mode competition on diode operation parameters is also identi- fied. Initial particle-in-cell simulations using MAGIC code have been carried out, and the results were in general agreement with those obtained in the experiments.