A Wideband Angularly Stable Cross-Polarization Converter With High Efficiency and RCS Reduction

Abstract

A low-profile, compact, and wideband reflective cross-polarization converter (CPC) metasurface is proposed. The unit cell, consisting of an l-shaped metallic strip and a diagonally shifted square patch, has a periodicity of $0.168{\lambda }_L$, where ${\lambda }_L$ is the wavelength at the lowest operating frequency. The structure is printed on a thin FR-4 dielectric layer of thickness $0.005{\lambda }_L$ and incorporates a 4.5 mm air gap ($0.094{\lambda }_L$), backed by a copper ground plane, resulting in a total thickness of $0.099{\lambda }_L$. The proposed design achieves an average polarization conversion ratio (PCR) above 90% over a wide fractional bandwidth of 91.14% (7.29–19.52 GHz). Under oblique incidence, the average PCR remains above 93% up to $45^{\circ }$. The wideband polarization conversion mechanism is explained through surface current analysis and an equivalent circuit model for both co- and cross-polarized reflection coefficients. A planar checkerboard configuration, formed by arranging the CPC unit cell and its mirror-symmetric counterpart, achieves more than 10 dB monostatic RCS reduction over 7.04–18.58 GHz (90.1% fractional bandwidth) for normal incidence, with an average reduction of 17.71 dB compared to a copper sheet. Owing to its thin profile, the structure maintains satisfactory conformal performance under bending. A 5 dB RCS reduction is preserved over 6.02–19.12 GHz (104.21%) at $60^{\circ }$ bending with an average reduction of 14.41 dB. For $30^{\circ }$ and $90^{\circ }$ curvature angles, bandwidths of 6.77–19.47 GHz (96.80%) and 7.26–18.64 GHz (87.88%) are achieved, with corresponding average RCS reductions of 10.74 dB and 9.19 dB, respectively. The fabricated prototype demonstrates efficient wideband RCS reduction in both planar and conformal checkerboard configuration states, confirming its suitability for stealth applications.