A radar level gauge system, for determining a filling level of a product contained in a tank, said radar level gauge system comprising: a transceiver (10; 20) for generating, transmitting and receiving frequency-modulated electromagnetic signals; a transmitting propagating device (3; 24; 40; 45; 50) electrically connected to said transceiver (10; 20) and arranged to propagate transmitted electromagnetic signals towards a surface of the product contained in the tank; and a receiving propagating device (3; 26; 40; 45; 50) electrically connected to said transceiver (10; 20) and arranged to return echo signals resulting from reflections at impedance transitions encountered by the transmitted electromagnetic signals, including a surface echo signal resulting from reflection at said surface, back to said transceiver, wherein said transceiver (10; 20) comprises: a signal generator for generating a frequency-modulated signal (S G) having a predetermined center frequency; a transmitter branch connecting an output of said signal generator with said transmitting propagating device via a first frequency converter for converting the frequency of said frequency-modulated signal (S G) to provide said transmitted electromagnetic signal (S T); a receiver branch connected to said receiving propagating device for receiving said surface echo signal (S R); a mixer having a first input connected to said signal generator and a second input connected to said receiver branch, for forming an intermediate frequency signal (S IF) indicative of a phase difference between said transmitted electromagnetic signal (S T) and said surface echo signal (S R); and processing circuitry connected to said transceiver for determining said filling level based on said intermediate frequency signal (S IF), characterized in that said first input of said mixer is connected to said signal generator via a second frequency converter for converting the frequency of said frequency-modulated signal (S G), and in that a signal isolation between said transmitting propagating device and said receiving propagating device is at least 30dB for said transmitted electromagnetic signals and said echo signals. a transceiver (10; 20) for generating, transmitting and receiving frequency-modulated electromagnetic signals; a transmitting propagating device (3; 24; 40; 45; 50) electrically connected to said transceiver (10; 20) and arranged to propagate transmitted electromagnetic signals towards a surface of the product contained in the tank; and a receiving propagating device (3; 26; 40; 45; 50) electrically connected to said transceiver (10; 20) and arranged to return echo signals resulting from reflections at impedance transitions encountered by the transmitted electromagnetic signals, including a surface echo signal resulting from reflection at said surface, back to said transceiver, wherein said transceiver (10; 20) comprises: a signal generator for generating a frequency-modulated signal (S G) having a predetermined center frequency; a transmitter branch connecting an output of said signal generator with said transmitting propagating device via a first frequency converter for converting the frequency of said frequency-modulated signal (S G) to provide said transmitted electromagnetic signal (S T); a receiver branch connected to said receiving propagating device for receiving said surface echo signal (S R); a signal generator for generating a frequency-modulated signal (S G) having a predetermined center frequency; a transmitter branch connecting an output of said signal generator with said transmitting propagating device via a first frequency converter for converting the frequency of said frequency-modulated signal (S G) to provide said transmitted electromagnetic signal (S T); a receiver branch connected to said receiving propagating device for receiving said surface echo signal (S R); a mixer having a first input connected to said signal generator and a second input connected to said receiver branch, for forming an intermediate frequency signal (S IF) indicative of a phase difference between said transmitted electromagnetic signal (S T) and said surface echo signal (S R); and processing circuitry connected to said transceiver for determining said filling level based on said intermediate frequency signal (S IF), characterized in that said first input of said mixer is connected to said signal generator via a second frequency converter for converting the frequency of said frequency-modulated signal (S G), and in that a signal isolation between said transmitting propagating device and said receiving propagating device is at least 30dB for said transmitted electromagnetic signals and said echo signals.