A novel design of aperture-coupled microstrip antenna with ultra-wideband low radar cross section (RCS) is proposed. Hybrid frequency selective surface (FSS) structures consisting of two kinds of polarizationdependent folded split ring resonators (PDFSRRs) and square patches are utilized to replace the conventional metallic ground. By orthogonally arranging the PDFSRRs in a chessboard-like configuration, the band-stop characteristic contributes to the gain enhancement, while the zero degree

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... ection phase points and wave-transmission characteristic are utilized to achieve RCS reduction both in-band and out-of-band. Furthermore, with square patches periodically etched on the bottom of FSS structures, a new zero degree reflection phase is introduced to enhance the effect of RCS reduction. Full wave simulations and measurements demonstrate that the proposed antenna achieves RCS reduction from 1 GHz to 18 GHz and gain enhancement compared with traditional microstrip antenna.