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Dual-Polarized Bandpass Three-Dimensional FSS Based on Square Waveguide Structure

We propose a novel bandpass three dimensional (3D) frequency selective surface. In the periodic unit cell, there are two gridded-square patch (GSP) resonators and a square waveguide filled with air. By the electromagnetic coupling between the two GSP resonators, two transmission poles are produced. Thus, a second-order bandpass response is achieved, and its 3dB fractional bandwidth is 25.12%. In addition, the square waveguide enhances the coupling. A simple equivalent circuit model is constructed and investigated so as to clarify the working principle. The results demonstrate the proposed design exhibits wide 3dB fractional bandwidth, dual polarizations, and good angular stability.