Testing of electrical components is of vital interest for the industry and has therefore become a main research area in instrumentation and measurement. The characterization spreads from DC measurements up to measurements at RF frequencies. For the higher frequency range scatter parameter measurements using network analyzers (NA) are widely used to characterize the components. However, most NAs are 2-port NAs making the characterization of a n-port time consuming as all ports have to be connected in the course of the measurement process. In this paper we present a methodology to estimate the full scatter matrix of a passive 4-port by means of local 2-port measurements only.