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In this article, a programmable reflectarray antenna (PRA) for 5G network in the S-band is proposed. The first 2-bit reconfigurable polarization-insensitive metasurface with two substrates, three metal layers, and only four p-i-n diodes in each unit cell is developed. The top layer of the proposed unit cell is a slotted polygon patch around with two pairs of p-i-n diodes integrated orthogonally. The 2-bit reflection phase correction is obtained by switching the four on-off states of the corresponding pair of p-i-n diodes. The square-ring slot and vertical slot on the polygon patch is proposed to suppress the cross-polarization level (XPL), which is the bottleneck problem of realizing the polarization-insensitive unit cell with 2-bit phase correction. A prototype PRA with $12\times 12$ unit cells is designed, fabricated, and tested. The measurements are in good agreement with expectations and full-wave simulations. The proposed PRA has the capability of 2-D beam steering within 60° with the maximum aperture efficiency of 31.20% at 3.5 GHz. The proposed reflectarray has the advantages of simple structure, minimum number of p-i-n diodes, high aperture efficiency, and polarization insensitivity.