Patent ID: 7586435

Claim:
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 for generating, transmitting and receiving electromagnetic signals within a frequency range; a waveguiding structure arranged to extend into said product contained in the tank and to guide a transmitted signal from said transceiver towards a surface of said product and to guide 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; a plurality of reference impedance transitions provided substantially periodically along said waveguiding structure with a distance between adjacent reference impedance transitions that is selected such that signals resulting from reflection of said transmitted signal at each of said reference impedance transitions combine to form a reference signal having a frequency within said frequency range; and processing circuitry connected to said transceiver for determining a propagation velocity of said electromagnetic signals in a medium inside the tank above said surface of the product based on said frequency of said reference signal and said distance between adjacent reference impedance transitions, and determining said filling level based on said surface echo signal and said propagation velocity.