Abstract: A system for the coherent demodulation of Binary Phase Shift keying (BPSK) signal at a frequency f, includes recovering a carrier signal (C) at a frequency 2f from the BPSK signal; injecting the signal having a frequency 2f in an injection locking oscillator (ILO), which has a natural resonant frequency fr which is substantially equal to f, to provide differential output (Op, On) signals which recover the original carrier with a phase shift of (?e?k)/2, where ?e=arcsin ((fr?f)/(?Aif)) where ? and k are parameters that depend on the type of predominant non-linearity in the injection locking oscillator (ILO), and Ai is the amplitude of the recovered carrier signal at a frequency of 2f, and combining the differential output (Op, On) signals with a copy of the incoming BPSK signal to generate a demodulated signal (DEMOD).