A backplane electrical connector having a pin header that includes a one piece housing supporting a plurality of columns of edge coupled differential signal pairs of contacts each separated by a ground contact. The pin header housing base is formed with a plurality of air passageways extending through the base, including an air passageway disposed between each signal contact in one column and an immediately adjacent signal contact in an adjacent column for electrically isolating the adjacent signal contacts from each other by an air dielectric medium. Core outs which extend only partially through the housing base are provided between each signal contact and an adjacent ground contact in an adjacent column for further isolating differential signal pairs.
