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In this Letter, a three-dimensional (3D) frequency selective surface (FSS) is proposed, exhibiting a dual-bandpass response with high selectivity and small band ratio. The unit cell of the presented 3D FSS consists of a pair of gridded double square loops (GDSLs) and a waveguide structure. Multiple transmission zeros and transmission poles are obtained from the electromagnetic coupling between the GDSLs. The electromagnetic coupling is enhanced by the waveguide structure, resulting in a dual-passband behaviour with high selectivity. Double square loops are designed to locate close to obtain a small band ratio. The measured results of the implemented FSS agree well with the simulated ones, which show that the proposed design can achieve the desired response to variations of incident angle from 0°to 60°for both TE and TM polarisations.