Angle modulation of frequency locked Gunn oscillators

It is shown experimentally and theoretically that frequency modulation through the bias circuit of free-running Gunn oscillators at low modulation frequencies can be converted to an equivalent phase modulation by frequency locking. Judicious choice of locking bandwidth causes the low-frequency phase-modulation coefficient to be of the same order of magnitude as that measured at high modulation frequencies. The phase-modulation coefficient at high frequencies is unaltered by frequency locking.