Radio telescopes rely on calibration to provide high-quality images. Here, we present a polarizing metasurface that can be used to aid the calibration of all-sky radio telescopes. The metasurface is intended for the REACH telescope, which will be used to study the early epochs of the Universe. The polarizing metasurface successfully transforms the polarization of a radiation pattern of a test antenna within the frequency range 90 to 165 MHz (apart from a narrow band around 155 MHz). The dielectric losses in the metasurface are estimated to be below 2%. Future work to improve the performance of the polarizer is outlined.