The Vircator generates microwaves at 5.17GHz with several hundred MW and at 774GHz with several MW in our experiments.According to the single charge sheet model of the Virtual Cathode Oscillator, the microwave at 5.17GHz is produced by the oscillation of the virtual cathode itself;the microwave at 7.74GHz is produced by the interaction of the oscillation of the virtual cathode and the modulated eleｃtron beam by the oscillation of the virtual cathode or the reflected eleｃtron beam.