This paper describes the design and measurement of a two-layers gangbuster Frequency Selective Surface (FSS). The FSS is aimed to limit the RCS of the compartment of a ship's mast housing telecommunication antennas and should guarantee a pass-band at low frequencies, in the operating band of the antennas, while reflecting the incoming signal at higher frequencies, up to 20 GHz. Based on the design, a panel has been manufactured and measured in three frequency bands: S-band, X-band and quasi L-band. The measurement results obtained for the first two bands are in good agreement with the simulations. Measurements in the third band pose some challenges and required defining a new ad-hoc measurement setup.