2-antenna complex correlation interferometer


A visibility is a complex quantity.



A single correlator (=multiplier+integrator) samples only the real part of a visibility, i.e. the cos term. Introducing a 90 degree phase shifter and using a second, independent correlator to register this signal, one samples both the real and imaginary part.



The big advantage is that, because the noise of the two correlators is independent, one gains a factor of .