Patent ID: 7027786

Claim:
A method of coherent down-conversion, comprising: receiving an electromagnetic (EM) input signal; generating a sub-harmonic local oscillator (LO) signal that is at least one of frequency coherent and phase coherent with the EM input signal; and down-converting the EM input signal using said sub-harmonic LO signal; wherein said step of generating comprises, dividing the EM input signal into a direct signal and a coupled signal; comparing the coupled signal with a harmonic of said sub-harmonic LO signal, and generating an error signal representative of a difference between said coupled signal and said harmonic of said sub-harmonic LO signal; up-converting said error signal according to a reference LO signal, resulting in an up-converted signal having harmonics that repeat at multiples of a frequency of said reference LO signal; selecting said sub-harmonic LO signal from said up-converted signal for said down-converting step; and selecting a harmonic of said sub-harmonic LO signal for said comparing step.