Analysis of uncertainty in visibilty samples via average correlation in a synthetic aperture interferometric radiometer

Quadrature Errors and DC Offsets Calibration of Analog Complex Cross-Correlator for Interferometric Passive Millimeter-Wave Imaging Applications

“…Each complex cross-correlation measurement via the interferometric imaging system can be named as a sample of the visibility function [ 11 ]. Based on the van Cittert–Zernike theorem [ 12 ], the radiometric temperature distribution in the field of view is equivalent to the inverse Fourier transform of the visibility function samples [ 9 , 13 ]. Since the cross-correlator is used to implement visibility function measurement [ 9 , 14 , 15 , 16 , 17 , 18 ] in the interferometric imaging systems, and since the image of the source of interest is derived by using the measured visibility [ 10 ], the cross-correlator is a vital component and the quality of the image is significantly affected by the output characteristics of the cross-correlator.…”

“…In comparison, analog correlators are more suitable for high brightness sensitivity observations due to their large bandwidth and low cost [ 14 , 15 , 16 , 19 , 20 , 21 , 22 ]. A digital correlator with a 180 MHz bandwidth has been adopted in our prototype security scanner [ 13 , 23 ], but in order to increase the imaging sensitivity at a relatively low cost, an analog complex cross-correlator operating over 1.5–2.5 GHz was proposed in our previous publication [ 15 ]. However, for practical analog complex correlators, the quadrature amplitude error and the quadrature phase error will degrade the sensitivity of the correlator and lead to the distortion of the measured visibility function; additionally, the outputs DC offsets would also cause offsets in the measured visibility and would influence the outputs dynamic range of the correlator [ 20 , 21 , 24 ].…”