In this paper the authors present a novel multiport probing fixture for high frequency measurements of dense via arrays. The probing fixture consists of a 36 mm by 36 mm multilayer printed circuit board plugged into an LGA socket clamped down to the device under test using custom hardware. The test signal is launched from top surface mounted coaxial connectors and fanned in with striplines to a 1 mm via pitch on the bottom side. Custom calibration substrates are used to deembed the probing fixture from measurements by applying multiport deembedding techniques. The effect of contact pressure on obtaining reproducible measurements is investigated. © 2011 IEEE.