An electrical connector system includes a backplane connector having a housing, signal contacts held by the housing and shield plates held by the housing. The housing includes a front and a rear. The housing includes signal channels extending along mating axes thereof between the front and the rear. The signal channels receive corresponding signal contacts. The housing includes slots that receive the shield plates. The signal contacts extend along the mating axes and are arranged in pairs carrying differential signals. The shield plates are electrically conductive and extend generally parallel to the mating axes between corresponding pairs of signal contacts to entirely peripherally surround the pairs of signal contacts to provide electrical shielding for the pairs of signal contacts.