Improvement of the pull in range and acquisition time of a microwave PLL system by injection locking the V.C.O

Abstract

The requirements of large pull-in range and short acquisition time in microwave and millimeter wave phase locked oscillators are of great importance since the free running VCO frequency may be sorne tens of MHz off the reference frequency. A substantial improvement can be obtained by injection-locking the V.C.O. to the reference signal; as a result, the V.C.O behaviour changes to a phase controlled fixed frequency oscillator, giving a reduction by one in the system order. Then, frequency acquisition is performed by the injection-locking process, and phase tracking is made by the P.L.l. system. We present experimental comparisons between a microwave P.l.l. system operating at 11 GHz, with an without injection-locking synchronization.