Ka-Dual-Band Oblique-Incidence Multi-Layer Metasurface for Linear to Circular Polarization Conversion

A dual-band linear-to-circular polarization converter is presented for Ka-band mobile satellite communication antennas operating under variable incidence. The converter operates in transmission mode, providing left-hand circular polarization (LHCP) at 20 GHz for signal reception and right-hand circular polarization (RHCP) at 30 GHz for signal transmission (or vice versa with a mechanical rotation of 90°). The polarizer consists of three anisotropic metasurfaces separated by two identical dielectric layers, with low-loss impedance transformers on both sides to improve matching and maintain stable performance up to 60° incidence. The total thickness of the structure is 8.4 mm. Each metasurface unit cell integrates two distinct metallic inclusions: an electric-LC (ELC) split-ring resonator (SRR) and a meander-line element. The meander-line elements are oriented at 45° with respect to the incident linearly polarized electric field. The proposed methodology focuses on optimizing unit cells for oblique incidence, where mode coupling must be considered. The design targets angle-stable susceptances that enable linear-to-circular polarization conversion over two wide frequency bands. Prototypes are fabricated and experimentally characterized through S-parameter measurements over the 18–32 GHz frequency range. Measurement results exhibit excellent agreement with full-wave simulations. The polarizer achieves near-unity transmittance, high polarization conversion efficiency, insertion loss below 2 dB, and an axial ratio below 3 dB over bandwidths exceeding 2 GHz—namely, 19–21 GHz and 29–31 GHz. Furthermore, the structure maintains robust angular stability for incidence angles ranging from 0° to 60°. These results demonstrate the design’s suitability for a broad range of commercial and military applications.