Miniaturised wideband metasurface polarisation converter with high angular stability

This paper presents a single-layer miniaturised wideband transmissive linear-to-circular (LTC) polarisation converter. The unit cell employs symmetrically arranged meandered metallic strips with engineered gaps that govern its resonance behavior. The meandered geometry increases inductance, reduces electrical size, and enhances polarisation conversion efficiency. The metasurface converter achieves wideband LTC conversion for both x- and y-polarised incidences from 5.23 to 12.85 GHz, corresponding to an 84.3% fractional bandwidth, with an axial ratio (AR) below 3 dB. It exhibits high angular stability, sustaining performance up to 85° for the transverse electric mode and 60° for the transverse magnetic mode. Within the AR bandwidth, the insertion loss remains low at 1.6–2.69 dB. The metasurface features an ultra-thin profile of 0.0038 λo with compact lateral dimensions of 0.0904 λo × 0.0904 λo, where λo denotes the wavelength at the center frequency (9.04 GHz) of the AR bandwidth. Both numerical simulations and experimental measurements validate its effectiveness in delivering wideband, wide-angle stable polarisation conversion with high transmission efficiency.