The present invention relates a transmission line probe for use in a radar level gauge system configured to determine a filling level (L) and a density of a product contained in a container, wherein the transmission line probe comprises: at least one probe line adapted to guide an electromagnetic transmit signal (ST) towards and at least partly through the product, and to guide an electromagnetic return signal (SR) back from a surface or interface of the product; and a plurality of insulating dielectric beads arranged along the at least one probe line and configured to decrease electromagnetic signal attenuation caused by the product. The present invention also relates to a radar level gauge system comprising such a transmission line probe, and to a corresponding method.