It is provided a vectorial network analyzer, comprising an input and output measuring device; a beat source for generating an optical beat signal; an optical transmission device which divides the optical beat signal into at least one first and one second partial signal, wherein the transmission device conducts the first partial signal to at least one terahertz transmitter and the second partial signal to at least one terahertz receiver and/or to at least one terahertz reference receiver; and a phase changing unit for varying the phase of the first and/or the second partial signal of the optical beat signal.