Many applications in aerospace and defense require a defined magnitude and phase relation between several signals, e.g. to design smart antenna arrays and its distribution networks or to ensure accurate phase between different transmitter or receiver chains of T/R modules. Measurement of magnitude can be done with spectrum analyzers, power meters etc. For a phase measurement, a VNA is the easiest, fastest and most accurate instrument. This application note shows how to accurately measure the phase between several signals by means of vector network analyzers of the R&S®ZNA, R&S®ZNB and R&S®ZNBT families.