Central to any interferometer is the correlator which brings together the signals from the individual antennas. The correlator cross-multiplies complex-valued measurements of the radio-frequency (RF) electric field produced by pairs of antennas to produce visibilities, which are related to the spatial brightness distribution of the sky by a transformation which, in the small-field-of-view flat-sky limit reduces to a Fourier transformation. These complex visibilities are summed over some short period of time, equivalent to taking a finite-length exposure of the sky, before being stored for subsequent calibration, gridding, image formation and deconvolution.

People involved: Changhua Li; Xuelei Chen, Tianhaijun, Xuyang