The present invention relates to a controllable barrier layer against electromagnetic radiation, to be used, inter alia, as a radome for a radar antenna for instance. The barrier layer comprises a first frequency selective layer (4) of a given geometric shape, said frequency selective layer transmitting radiation of a certain polarization within a desired frequency band and reflecting radiation of a different polarization and radiation outside said band and at least a second identical frequency selective layer, which is placed close to or in connection with the first layer in the radiation direction. The layers are configured to be placed in a first position relative to each other so that they together obtain transmission properties similar to those of the first layer alone and in a second position relative to each other so that they together reflect radiation of said certain polarization within said desired frequency band.