Polarization-Insensitive High-Angular Stable Frequency Selective Surfaces Based on Anisotropic Artificial Electromagnetic Medium

A novel method of designing broadband wide-angle frequency selective surface (FSS) is proposed. First, based on effective media theory, perfect transparency can be realized for FSS when the equivalent permittivity equals permeability, which provides transmission poles. Second, the effective permeability and permittivity can be regulated by electrical resonance and magnetic resonance. A second-order passband is realized by adjusting the electromagnetic parameters with a folded dipole and metal wire in the FSS. The transmission zero is introduced to improve the selectivity on the low-frequency side. Third, a new transmission pole is introduced to extend the passband width by loading square rings onto the upper and lower layers. Note that the conditions of $\varepsilon _{t}\varepsilon _{n} =1$ and $\mu _{t}\mu _{n} =1$ guarantee the angular stability of the broadband FSS. For demonstration, one FSS prototype is fabricated and measured. The results indicate a wide bandwidth of 41% with insertion loss of less than 1.3 dB and good angular stability under an oblique incident angle of 60° for dual-polarization application.