Protector for one or more electromagnetic sensors

A frequency-selective surface designed to transmit (allow to pass through) electromagnetic radiation around one or more predetermined transmission frequencies. The frequency-selective surface comprises at least two layers, whereby the outer layer is made up of at least one electromagnetic reflecting layer with a periodic pattern of conductive elements. The periodic pattern of conductive elements is made to have a reflection resonance frequency for electromagnetic radiation which is of the order of three times higher than the desired transmission frequency. The inner layer is placed at a suitable predetermined distance from the outer layer. The inner layer is made up of at least one electromagnetic transmitting layer having a periodic pattern of aperture elements. The periodic pattern of aperture elements is made in order to have a transmission resonance frequency for electromagnetic radiation which is substantially the same as the desired transmission frequency.