Narrow-band microwave generation from an oscillating virtual cathode in a resonant cavity

An experimental approach using a high Q, resonant cavity surrounding an oscillating virtual cathode has achieved frequency stabilization, and repeatable narrow-band operation of the virtual cathode microwave source. A cylindrical cavity resonator is used with the microwave power being extracted radially through circumferential slot apertures into dominant-mode L-band waveguide. The electron-beam/cavity interaction produces strong feedback between the induced cavity field and the oscillating virtual cathode, forcing it to lock to the resonant frequency of a cavity mode over a large variation in electron beam current. The 3-dB frequency bandwidth observed during single 100-ns pulses is less than 1%. The 3-dB bandwidth appears to be limited by the finite temporal width of the microwave pulse.