3-D Waveguide FSS by Coaxial Square Tubes

In this paper, a novel three-dimensional frequency selective structure (3-D FSS) based on the waveguide concept is proposed. The unit cell of the 3-D FSS is formed by coaxial square tubes (CoSTs), which provides two propagation paths between the adjacent tubes. Moreover, the gap between the adjacent unit cells forms another propagation path. The three propagation paths will introduce three transmission poles and three transmission zeros. With proper design, the proposed 3-D FSS exhibits a stable third-order bandpass frequency response under oblique incident angles for dual polarizations. Mode analysis is presented for understanding the proposed 3D FSS. In addition, using the printed circuit board (PCB) technique, the proposed 3-D FSS are easy for fabrication.