Abstract: A dual-polarized, highly-selective tri-passband three-dimensional frequency selective surface (3D FSS)is proposed. The unit cell of the proposed 3D FSS consists of four layers of square dielectric tubes, which provides one parallel plate waveguide (PPW) path and three square coaxial waveguide (SCW) paths. Owing to the electromagnetic coupling between two same short SCW resonant elements in each SCW path, original single resonant mode provided by the square slot on the end face of SCW path will split into even- and odd-resonant modes, introducing two transmission poles, and then forming a second-order passband. Thus, three SCW paths can realize three second-order passbands. In addition, the electromagnetic waves in different paths are combined out-of-phase,which can generate multiple transmission zeros and improve the frequency selectivity of this FSS.In order to explain the operating principle of the proposed 3D FSS, the distributions of electric-field vector at the frequencies of the transmission zeros/poles are investigated. The simulated results show that the proposed 3D FSS exhibits stable frequency responses to variations of incident angle from 0° to 60° under both transverse electric (TE) and transverse magnetic (TM) polarizations. Meanwhile,this 3D FSS has small band ratios and relatively compact unit cell size.

Key words: frequency selective surface (FSS), tri-passband, three-dimensional (3D), high selectivity, dual polarizations, band ratio