PHASE-LOCKING OF A 2ND-HARMONIC GYROTRON OSCILLATOR USING A QUASI-OPTICAL CIRCULATOR TO SEPARATE INJECTION AND OUTPUT SIGNALS

Phase-locking in a 34.5-GHz special complex cavity gyrotron oscillator operating at the second harmonic of the electron cyclotron Frequency was studied, Injection of the locking power was made via a quasi-optic al circulator connected to the gyrotron output. Locking bandwidth was measured by comparing the phase of the injection signal and output sig nal using a balanced mixer, Locking was observed with input power leve l as low as 40 dB below the gyrotron output power, The locking bandwid th is, however, narrower than in gyrotrons operating at the fundamenta l cyclotron frequency which may be attributed to the longer resonant c avity in the second harmonic gyrotron and the corresponding larger val ue of external quality factor, The measurements are roughly in agreeme nt with predictions of Adler's phase-locking equation which is given f or our system in terms of powers propagating in the output waveguide t oward and away from the gyrotron cavity.