“…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 ].…”