In this paper, we propose, design, fabricate and test an interposer that provides a convenient and stable connection between a via-array-type device under test (DUT) and coaxial interface measurement instruments in a frequency band up to 20GHz. A 3D EM model based de-embedding technique is adopted to remove the influence of the interposer from measurements. The validity and repeatability of the apparatus and de-embedding technique are verified by comparing to microwave probe measurements on individual channels. The impact of misregistration arising from PCB fabrication is analyzed based on the measurements of up to three differential pairs in adjacent layers using a 12 port configuration. © 2011 IEEE.