The cross-polarization backscatter positioning system based on the information-energy decoupling mechanism can achieve high gain and obstacle avoidance advantages while reducing the number of positioning antennas. A novel dual-band quad-polarized antenna design with in-band radar cross section (RCS) reduction using polarization conversion metasurface (PCM) for IoT anti-multipath indoor positioning is first proposed in this article. At first, a dual-band reflective miniaturization PCM unit is designed to analyze the relationship between the polarization conversion band and in-phase reflection band under u- and v- polarized incident waves. This provides theoretical support for PCM to simultaneously achieve radiation enhancement and in-band RCS reduction. Then, a dual-band shaping dipole antenna is designed as a radiator. Finally, a dual-band Wilkinson power divider and Butler matrix are designed to feed the$2\times 2$dipole array to achieve quad-polarization. In the overall design of the antenna, according to the principle of in-phase reflection in the dual-band, every$4\times 4$subarray of PCM is used as a reflector for every dipole antenna in the v direction to realize unidirectional radiation and low-profile design. The quad-polarization of X, Y, left-hand circular polarization (LHCP), and right-hand circular polarization (RHCP) is achieved within the bandwidths of 0.85–0.93 GHz and 2.38–2.5 GHz. Based on the principle of reflection phase cancellation in the dual-band, an$8\times 8$arrangement of PCM units with their mirror units is designed to achieve in-band monostatic RCS reduction in the dual-band range of 0.745–1.02 GHz and 2.1–2.67 GHz. Therefore, this antenna is highly suitable for the application of item-level high-precision cross-polarization positioning systems in multiconductor environments with indoor deployment of multiple IoT nodes.