Abstract: A new type of unit that uses polarization conversion metasurfaces (PCM) to reduce the radar cross section (RCS) and maintain the radiation characteristics of slot antenna arrays is proposed. The PCM is composed of slotted rectangular patches arranged obliquely at 45°, which are placed on the upper surface of the slot array antenna. This paper analyzes the characteristics and principles of RCS reduction. Simulation and experimental results show that the single-site RCS reduction bandwidth of the slot antenna array with PCM is 8.0～21.8 GHz under the impact of x-polarized and y-polarized waves. At the same time, the antenna’s radiation characteristics are well maintained in terms of impedance bandwidth, gain, and radiation pattern.