Instantaneous frequency measurement (IFM) receiver with only two delay lines

Claim 1

An IFM receiver having a plurality of correlators, with an individual delay line in each correlator, means coupling an RF signal source to each correlator, each correlator having phase discrimination means, detector means and differential amplifier means to provide output signals proportional to sin ωτ and cos ωτ, ω being an angular frequency of an RF signal from the RF signal source, and logic means using said output signals to derive a phase value for each correlator, the phase value being a remainder less than 2π for ω, any multiples of 2π being lost so that there is an ambiguity in the value which is resolved by comparing the outputs of the plurality of correlators; the improvement in which there are two correlators and therefore two delay lines, said two delay lines having lengths a and b respectively which are relatively prime, said logic means provides respective remainder phase values r 1 and r 2 less that 2π for the two correlators, and frequency-determining means for finding the frequency of an RF signal using the equations r.sub.1 =ωa-m·2π (1) r.sub.2 =ωb-n·2π (2) where m and n are unknown integers.