A radar level gauge system, for determining a filling level of a product in a tank, said radar level gauge system comprising: a transceiver for generating, transmitting and receiving electromagnetic signals having a center frequency within a frequency band; a multi-conductor probe electrically coupled to said transceiver and arranged and configured to guide an electromagnetic transmit signal from said transceiver towards and into said product in the tank, and to return an electromagnetic surface echo signal resulting from reflection of said transmit signal at a surface of said product back towards said transceiver, said multi-conductor probe comprising a first probe conductor and a second probe conductor extending together from an upper probe end to a lower probe end; a plurality of spacers distributed along the multi-conductor probe for controlling a positional relation between the first probe conductor and the second probe conductor; and processing circuitry for determining said filling level based on said transmit signal and said surface echo signal, wherein each spacer in said plurality of spacers is configured to allow fluid flow along said multi-conductor probe past said spacer, wherein each spacer in said plurality of spacers has a spacer extension along said multi-conductor probe, corresponding to at least a quarter of a wavelength of the transmit signal at said center frequency, and wherein each spacer in said plurality of spacers is configured in such a way that said multi-conductor probe, within said spacer extension, exhibits a first probe portion with a first impedance, a second probe portion with a second impedance, and a third probe portion, between said first probe portion and said second probe portion, with a third impedance lower than said first impedance and said second impedance. a transceiver for generating, transmitting and receiving electromagnetic signals having a center frequency within a frequency band; a multi-conductor probe electrically coupled to said transceiver and arranged and configured to guide an electromagnetic transmit signal from said transceiver towards and into said product in the tank, and to return an electromagnetic surface echo signal resulting from reflection of said transmit signal at a surface of said product back towards said transceiver, said multi-conductor probe comprising a first probe conductor and a second probe conductor extending together from an upper probe end to a lower probe end; a plurality of spacers distributed along the multi-conductor probe for controlling a positional relation between the first probe conductor and the second probe conductor; and processing circuitry for determining said filling level based on said transmit signal and said surface echo signal, wherein each spacer in said plurality of spacers is configured to allow fluid flow along said multi-conductor probe past said spacer, wherein each spacer in said plurality of spacers has a spacer extension along said multi-conductor probe, corresponding to at least a quarter of a wavelength of the transmit signal at said center frequency, and wherein each spacer in said plurality of spacers is configured in such a way that said multi-conductor probe, within said spacer extension, exhibits a first probe portion with a first impedance, a second probe portion with a second impedance, and a third probe portion, between said first probe portion and said second probe portion, with a third impedance lower than said first impedance and said second impedance.