3X9?+= F Phase-Locking of a Second-I-Iarmonic Gyrotron Oscillator Using a Quasi-Optical Circulator to Separate Injection and Output Signals* - Ii. Z. Cue, 1).J. I{oppe, iVIEhl BKR, IEEE. J. Rodgers, R.A1. ]’erez, J.P. Tate, M~MB~R, IEEE, Il. ].. Conroy, V. I.. Grarlatsteinl F~I,I,o\v, IEEE, A. Bhanji, P.E. Latham, MEMB!ZR, IEEE, G.S. Nusinovich, SENIOR M~:MII~R, IEEE, and M. Naiman Phase-locking in a 34.5 G]lz special complex cavity gyrotroxl oscillator operating at the second harmonic of the electron cyclotron frecluency was studied. Injection of the locking power was made via a quasi-optical circulator connected to the gyrotron output. Locking bandwidth was measured by comparing the phase of the injection signal and output signal using a balanced mixer. Locking was observed with input power level as low as 40 dB below the gyrotron output power. The locking bandwidth is, however, narrower than in I gyrotrons operating at the fundamental cyclotron frequency which inay be attributed to the I longer resonant cavity in the second harmonic gyrotmn and the corresponding larger value of external quality factor. The measurements are roughly in agrmment with predictions of I Adler’s phase-locking equation which is given for our system in terlns of powers propagating in the output waveguide toward and away from the gyrotron cavity. I ● The research described in this paper was carried out in part by the Jet Propulsion Lab- 1 oratory, California Institute of Technology, under a contract with the National Aeronautics I and Space Administration; in addition, this wcjrk was supported in part by the DoD Vacuum Electronics Initiative and managed by the Air Force OfXce of Scientific Research under Grant AFOSR-91-0390. H.Z. Guo, J. Rodgers, V.L. Granatstein, P.E. Latham, G.S. Nusinovich, and M. Naiman are with the Institute for Plasma Research, University of Maryland, College Park, MD 20742. D.J. Hoppe, R.M. Perez, B.L. Conroy, and A. Ilhanji are with the Jet Propulsion Labo- ratory, Pasadena, CA 91109. J.P. Tate was with the [University of Maryland and is now with Florida A & M University, I Tallahassee, FL 32307. 1