An electrical connector includes a dielectric housing that holds pairs of signal modules adjacent one another. Each signal module includes a mating edge having a row of mating contacts, a mounting edge having a row of mounting contacts, and a plurality of conductors electrically connecting each mating contact with a respective mounting contact. The mating contacts in adjacent modules have a first contact spacing therebetween, and the mounting contacts in adjacent modules have a second spacing therebetween. The conductors in adjacent modules have a third spacing therebetween. The second and third spacings are selected to provide a pre-determined impedance through the signal modules.