A multifunctional bi-anisotropic metasurface with reflection-transmission polarization conversion and narrow bandpass transmission characteristics.

A novel multifunctional bi-anisotropic omega metasurface (MS) that simultaneously supports polarization transformation in both reflection and transmission modes, as well as narrow bandpass transmission functionality, is proposed by combining a patterned polarization-converting surface with a cross-dipole bandpass frequency-selective surface (BP-FSS). The BP-FSS, etched inside the metal ground, provides a reflection-transmission frequency response and acts as an equivalent ground plane. When the incident wave is illuminated from +Z-side (forward direction), the entire MS exhibits two reflective circularly polarized and cross-polarized bands separated by a low-loss bandpass window. Under the -Z-side (backward direction) excitation, the structure functions as a partial reflector (PR) outside the bandpass region without altering the polarization state of the incident wave. For both ±Z-sided excitation, the MS maintains symmetric transmission responses, realizing a narrow bandpass window with an insertion loss (IL) of less than - 1 dB and two partial transmissive cross-polarization (TCP) conversion bands. The proposed concept is validated through equivalent circuit models (ECMs) of the BP-FSS and the cascaded MS, along with measurements of a fabricated 17 × 29 unit-cell prototype, confirming excellent agreement with simulations. Compared with existing MSs, the proposed design uniquely combines multiple functionalities, making it a potential alternative to frequency-selective rasorbers and a promising candidate for antennas and communication system applications.