Double square loop FSS with slots for closer band spacing at oblique incidence

This paper proposes a modified nested double square loop Frequency Selective Surface (FSS) in order to achieve a higher FSS packing density. By introducing slots to a conventional square loop, a longer electrical length of the FSS and a lower ratio of l/λ can be accomplished. The optimized FSS prototype provides a maximum attenuation of more than 30 dB alongside with 270 MHz and 690 MHz bandwidth for the lower and upper resonant frequencies, respectively. Furthermore, the proposed structure also offers a stable frequency response for both TE and TM modes at normal and oblique incidence, up to 45°. The measured and simulated results are shown to be in a very good agreement with each other.