In this letter, a new bandpass frequency selective surface (FSS) with sharp sidebands is proposed to suppress electromagnetic interferences caused by the fifth generation (5G) mobile communication to fixed C-band satellite system. The proposed design is composed of three cascaded layers separated by air space, whose unit cell geometry comprises metal square loops, square slots and their evolvement. As the overall configuration yields high-order bandpass characteristics with multiple transmission poles and zeros, a flat passband covering 3.7-4.2 GHz is obtained, while the out-of-band shielding effectiveness mostly remains better than 20 dB over frequency lower than 6.5 GHz. Good angular stability and polarization independency are also achieved due to structural symmetry. A prototype was fabricated and measured, whose results agree well with the full-wave simulation.