Measuring system for measuring dielectric properties of a multiphase fluid flow in a pipe, the system including a microwave signal generator connected to the multiphase fluid flow for transmitting signals F OUT within a predetermined frequency range into said flow by applying signals F OUT to a microwave sensor constituted by a resonator, the resonator being expected to have a resonance peak within said frequency range , a signal receiver adapted to receive signals within said range from said flow, and analyzing means for calculating the dielectric properties based on the transmitted and received signals, wherein the signal generator includes: an IQ modulator being coupled to a high frequency oscillator and a low frequency synthesizer, wherein the high frequency oscillator is adapted to generate a high frequency signal f LO , in a range from a few MHz to several GHz; the low frequency synthesizer is adapted to generate signals f RF at a number of frequencies within a chosen frequency range lower that the high frequency signal, the chosen frequency being from a few hundred kHz up to some 10's of MHz, said IQ-modulator being adapted to generate an output signal IQ OUT constituted by the combination of said signals from the oscillator and the synthesizer, the predetermined frequencies of the oscillator and the synthesizer being chosen based on the required output frequency range for the IQ-modulator, the signal transmitted from the IQ modulator into the resonator thus being F OUT = f LO + f RF , and wherein the receiver includes an IQ demodulator receiving the signal (f LO + f RF (weak) ) from the resonator , the IQ demodulator also being connected to the IQ modulator for receiving said high frequency signal f LO , the demodulator thus converting the signal to a frequency in the range of an ADC so as to provide I and Q signals to the analyzing means configured to extract said dielectric properties of a multiphase fluid based on an analysis of the resonance frequency of the resonance peak in the received signal. wherein the high frequency oscillator is adapted to generate a high frequency signal f LO , in a range from a few MHz to several GHz; the low frequency synthesizer is adapted to generate signals f RF at a number of frequencies within a chosen frequency range lower that the high frequency signal, the chosen frequency being from a few hundred kHz up to some 10's of MHz, said IQ-modulator being adapted to generate an output signal IQ OUT constituted by the combination of said signals from the oscillator and the synthesizer, the predetermined frequencies of the oscillator and the synthesizer being chosen based on the required output frequency range for the IQ-modulator, the signal transmitted from the IQ modulator into the resonator thus being F OUT = f LO + f RF , and wherein the receiver includes an IQ demodulator receiving the signal (f LO + f RF (weak) ) from the resonator , the IQ demodulator also being connected to the IQ modulator for receiving said high frequency signal f LO , the demodulator thus converting the signal to a frequency in the range of an ADC so as to provide I and Q signals to the analyzing means configured to extract said dielectric properties of a multiphase fluid based on an analysis of the resonance frequency of the resonance peak in the received signal. <EOS>