Interaction of a vircator microwave generator with an enclosing resonant cavity

Interaction between a vircator microwave generator and a resonant cavity is produced by enclosing the virtual cathode inside a right circular cylinder appended to the anode foil. Cavity diameter is chosen to simultaneously minimize the number of resonant modes and to avoid significant perturbation of the virtual cathode formation. By varying the cavity length frequencies corresponding to the TM/sub 01n/ cavity modes are tuned to resonate with the broad band oscillating virtual cathode. The RF fields stored in the resonant cavities feedback on the virtual cathode and improve the kinetic to microwave power conversion efficiency. For each cavity only a single mode is excited; non-resonant frequencies are suppressed. Measured radiation patterns show that TM/sub 011/ mode microwave power extracted radially from the cavity is 1.5 times that with no cavity, and about 4 times that from a non resonant cavity. Resonant cavities suppress non-resonant frequencies decreasing the bandwidth of the emitting radiation by a factor ≥ 5