A broadband third-order antenna-filter-antenna based frequency selective surface at high oblique angle of incidence

A third-order miniaturized band-pass frequency selective surface (FSS) using Minkowski fractal islands is proposed with broader bandwidth and is designed specifically for an oblique incidence angle of 60°. The operating frequency band is 1 GHz to 16 GHz. FSS design is based on antenna-filter-antenna concept employing Minkowski fractal geometries for patches and a cross-shaped slot on the ground. Presented structure demonstrates a fractional bandwidth (BW) of 60% from 7 GHz to 13 GHz, which is corresponding to 3 dB BW of 6 GHz (from 7 GHz to 13 GHz) for both reflection (S
₁₁
) and transmission coefficients (S
₂₁
) at an incident angle of 60° and transverse electric (TE) polarization. Additionally, the performance is stable for varying incidence angle of electromagnetic wave within 60° (0° to 60°) examined with an increment of 10°. The operating mechanism along with details of designed FSS, the simulated results by Finite Element Method (FEM) are presented and also discussed. Resulting low profile FSS has a small unit size and gives a higher frequency selectivity along with three poles frequency response, compared to traditional third-order FSSs, therefore suitable for spatial filtering, reflector antennas, radar cross section (RCS) control and especially useful in radome of aircraft with a higher oblique incidence angle of 60°.