Dual resonant transmissive circular dichroism in a rotationally transformed chiral metasurface

Abstract An electrically thin bilayer chiral metasurface is presented for dual resonant, same handedness circular-polarization-selective transmission in the X-band. The 11 × 11 mm 2 connected unequal-arm unit cell produces forward right-handed circularly polarized (RHCP) circular dichroism (CD) maxima of 0.72 and 0.75 at 9.672 and 10.636 GHz within a common transmission window, with reciprocal backward left-handed circularly polarized (LHCP) selectivity and a complete CD null at 10.3 GHz. A controlled four-configuration comparison shows that the compound front–back transformation establishes chiral interlayer coupling, whereas unequal terminal paths enable the second modal contribution. Surface-current distributions identify a lower even mode, an intermediate mixed state, and an upper odd interlayer-coupled mode. A geometry-derived equivalent-circuit model reproduces the broadband full-wave transmission response, and free-space measurements of an aperture of 29.7 × 20.9 cm² validate the polarization-selective behavior. The demonstrated response supports passive circular-polarization-selective receiver front ends and provides a polarimetric sensing platform for non-contact CFRP assessment.