Why does linear phase shift cause mode locking?

The authors examine the character of signals in a simulated wide band oscillator. It is shown how a continuously changing phase shift (a fixed frequency shift) in the feedback path produces a response which resembles mode locking. The phase insertion or frequency shifting prevents the continuity of waves and the dominance of a single frequency component. It stimulates the growth of noise into wave trains which are easily synchronized by nonlinearity or by gain saturation, which of itself is insufficient to lock. Long term periodicities and fixed spectrum components are observed