Experimental study of intrinsic and technical phase noise in a second harmonic gyrotron amplifier (phigtron)

Summary form only given. The phigtron is a millimeter wave, frequency-doubling amplifier that has been demonstrated to produce 360 kW peak power with bandwidth of 0.6%, saturated gain of 30 dB and electronic efficiency of greater than 35%. The input signal, injected into a Ku-band fundamental gyro-TWT input section, modulated a 60 kV, 25 A electron beam produced by a MIG-type gun. After transit through a drift section, prebunching in the electron beam excited the TE/sub 03/ mode at twice the input frequency in an output cavity with a measured total quality factor of /spl sim/600. A substantial range of magnetic field profiles was surveyed using a computer-controlled system in order to optimize operating parameters with respect to output power, bandwidth and efficiency. A set of operating conditions was established and the phase noise performance was measured for both the saturated (360 kW output power) and linear gain (100 kW output power) cases. The phase noise at 100 Hz from the carrier was observed to be as low as -40 dBc/Hz. Furthermore, a high degree of correlation was established between sources of technical noise (e.g., fluctuations in beam voltage, current and magnetic field) and this value. The intrinsic phase noise was estimated to be at least 10 dB/Hz lower at the same frequency offset.