Abstract: In this paper, a wave-transmitting material with good band-pass filtering performance in the C and S bands is designed. The material has a periodic cell size of 10 mm and a structure thickness of 20 mm, revealing wave transmission performance in the band from 2.5 GHz to 5 GHz. The top mast of ships made from this material can greatly improve the electrical performance of the nearby antennas of the shipborne radars, especially the sidelobe level of antenna caused by the top mast. Compared with traditional materials made for the masts, the proposed material reduces the sidelobe levels of the antennas by 18.2 dB at the C band and 7.8 dB at the S band, and a decreased false alert rate can be obtained, showing its potential for future usage.