Design and Performnance of a Three-Cavity Gyroklystron Amplifier

The Naval Research Laboratory (NRL) is investigating the gyroklystron amplifier (GKA) concept. The purpose of this program is to assess GKA characteristics in order to determine if such a device is capable of achieving the high efficiency, gain, and output power predicted by numerous studies. The first in a series of tubes to examine GKA behavior has been fabricated and is currently under testing. This tube utilizes three rectangular cavities operating in the TE101 mode. Design goals included 100-kW output power, 30-percent efficiency, 40-dB gain, and operation at a center frequency of 4.5 GHz. Test results have shown reasonable agreement with theoretical predictions. In particular, efficiencies as high as 33 percent have been observed with a saturated output power of 52 kW. Bandwidths of 0.4 percent have been measured. In addition, the device can be operated under certain conditions as a phase-locked oscillator. These results suggest that the desirable characterstics which have been predicted for the GKA can be realized with a microwave tube.