Novel mode-selective gyrotron with a PBG resonator

Summary form only given. We report the design and experimental demonstration of a gyrotron oscillator using a photonic band gap (PBG) structure to eliminate mode competition in a highly overmoded resonator. The PBG cavity supports a TE(0,3) -like mode at 140 GHz and is designed to have no competing modes over at least a frequency range of 35 % about the design mode. The PBG resonator is formed by removing a few rods from a triangular lattice of metal rods to create a defect mode. The lattice parameters are chosen to have a band gap around the operating frequency which, results in the confinement of only the higher order design mode, while the other competing modes pass freely through the transparent lattice. Experimental operation of a 68 kV, 5 A gyrotron oscillator with the PBG resonator demonstrated 25 kW of peak output power in microsecond pulsed operation in the design mode. No other modes were observed over the full predicted operating range about the design mode. The present experiment is modeled on a previous experiment at MIT on a 140 GHz conventional cavity gyrotron oscillator operating in the TE(0,3) mode. The reduced mode competition observed in the present experiments represents a clear and dramatic improvement over earlier results with a conventional cavity. To our knowledge, the present results are the first use of a PBG cavity in an active microwave device. In the future, the advantages of the PBG structure demonstrated here could be extended to other vacuum electron devices, including the gyrotron amplifier and slow wave devices such as klystrons and traveling wave tubes.