Patent ID: 8040274

Claim:
An apparatus for ascertaining and/or monitoring the fill level of a medium in a container, comprising: an antenna, which transmits and receives high frequency signals in a predetermined oscillatory mode in a bounded space in a predetermined radiation direction; an antenna protection element situated in front of said antenna in the radiation direction, said antenna protection element having a material transmissive to the high frequency signals, and a surface of which condensate of the medium runs, and/or drops, off; and a control/evaluation unit which evaluates received high frequency signals and ascertains fill level, wherein: in the radiation direction, said surface of the antenna protection element is formed according to at least one periodic, symmetric function, which is matched to symmetry properties of the predetermined oscillatory mode of the high frequency signals; and coating of material transmissive for the high frequency measurement signal are provided, for improving antistatic properties, improving chemical and/or mechanical resistance and reducing said adhesive, or capillary, forces of the surface of the antenna protection element.