Miniaturised high-impedance surface with high angular stability of resonant frequency

A novel miniaturised high-impedance surface (HIS) is proposed that has a stable resonant frequency with respect to variation of incident angles for TE and TM-polarised waves. A unit cell of this structure consists of four spiral-shaped frequency selective surfaces at the interface of a grounded dielectric slab where the spirals are connected separately to the ground plane through four vias. Performance is compared to that of the mushroom and meander line-based HIS. For the same size of unit cells the resonant frequency of the proposed structure is close to half of that for the mushroom structure and 66% of that for the meander line-based HIS.