The present disclosure relates to a waveguide section having at least one air-filled waveguide conducting tube having an electrically conducting inner wall. Each waveguide conducting tube comprises has a plug-in filter device with two or more electrically conducting elements arranged in series and spaced apart by a connecting arrangement. Each plug-in filter device is adapted to be retained in the corresponding waveguide conducting tube using a dielectric holding arrangement such that the electrically conducting elements are spaced apart from the waveguide conducting tube. The electrically conducting elements are arranged to be electromagnetically coupled such that passing a radio frequency is electromagnetically filtered.