The context of the present thesis is the measurement of the scattering parameters of a device-under-test (DUT) employing vector network analyzers (VNA). The de-embedding of the DUT S-parameters from the total measurements that include the test-fixture contribution is investigated in detail. The fixtures are required to physically connect the DUT to the instrument and make the data acquisition possible, but their presence is making the measured S-parameters look completely different from the actual DUT ones. The scope of the present work is to provide a strategy to de-embed the DUT from the total, or fixture-DUT-fixture, measurements. In literature, the techniques to pursue this goal are many and are considering most of the time the two-port case.