A novel miniaturised single-layer square loop frequency-selective surface (FSS) designed and optimised for effective shielding in X-band is presented. The proposed FSS structure provides a wider bandwidth response of 4.0 GHz and it covers the X-band frequency (8–12 GHz) with a centre frequency of 10 GHz and attenuation of 39 dB. The proposed design compared the simulation results with equivalent circuit method results. Both achieved the same frequency response and bandwidth but the attenuation level is varied. Due to the symmetric structure,the proposed design achieves polarisation-independent characteristics and provides stable response at normal and oblique incidences for both TE and TM modes up to 60º. Both the measured and simulated results are in good agreement.