Abstract Reconfigurable intelligent surfaces (RISs) have emerged as a key technology for shaping smart wireless environments in next‐generation wireless communication systems. To support the large‐scale deployment of RISs, a reliable and efficient diagnostic method is essential for maintaining optimal performance. In this work, a robust and effective approach for RIS diagnostics is proposed using a space‐time coding strategy with orthogonal codes. The proposed method encodes the reflected signals from individual R…