Abstract: A dual-polarized ultra-wideband tapered slot antenna for a square kilometer Intermediate frequency aperture array is designed. The antenna adopts a pentagon resonator instead of the square cavity of the conventional tapered slot antenna, and expands the low-frequency working bandwidth without occupying the active circuit area. The antenna adopts a pentagon resonator instead of the square cavity of the conventional tapered slot antenna, and expands the low-frequency working bandwidth without occupying the active circuit area. The radiant panel and the feed balun are separated designed, thus, the size of the dielectric plate can be greatly reduced to save processing cost, and the electrical performance of the antenna can be maintained. The antenna is processed into a cross-shaped structure to achieve good current continuity in the array elements and not deteriorate the polarization performance of the antenna. The simulation results show that the antenna can scan in the bandwidth of 0.25-1.57 GHz and has better polarization characteristics in the whole working frequency band. Therefore, the design of antenna can fulfill the requirements of the Square Kilometer Array (SKA) in the ultra-wideband intermediate frequency, low cost, large scan angle and high polarization isolation.