Abstract: An apparatus for ascertaining and/or monitoring fill level of a medium in a container. The apparatus includes an antenna, which transmits and receives high frequency signals in a predetermined oscillatory mode in a bounded space in a predetermined radiation direction, wherein, in front of the antenna in the radiation direction, an antenna protection element of a material transmissive for the high frequency signals is provided, and wherein a control/evaluation unit is provided, which evaluates the received high frequency signals and ascertains the fill level.