In this article, a polarization-insensitive, higher angular stability, and single-layered miniaturized wide stop-band frequency selective surface (FSS) is presented for effective electromagnetic shielding over an extremely wideband (9-20 GHz). A simple square gridded unit cell exhibits wideband rejection with −10 and −20 dB fractional bandwidth of 150.7% (3.4-24.2 GHz) and 74.5% (9.14-20 GHz), respectively. The designed unit cell has miniaturized dimensions (0.09λ0 × 0.09λ0 × 0.018λ0) as compared to existing research works on wideband FSSs. An equivalent circuit model is developed for the rigorous analysis of the proposed structure. The outcome of this circuit model is validated, and it shows good agreement with the structure simulation results. The measured results bear close resemblance with the simulated results. This FSS can be used to provide shielding from harmful radiations over a wide frequency range and as a good reflector to improve the gain of wideband antennas. © 2021 Wiley Periodicals LLC.