Experimental Over-the-Air Diagnosis of 1-Bit RIS Based on Complex Signal Measurements

The reconfigurable intelligent surface (RIS), is regarded as a promising technology for enhancing wireless system performance. The RIS design typically comprises a substantial number of cost-effective RIS elements. RIS diagnosis, which aims at identifying faulty RIS elements, is essential to ensure the RIS functions as intended. In this letter, a low-cost, robust, fast, yet highly effective over-the-air (OTA) diagnosis method based on complex signal measurements is proposed to detect the faulty phase shifters in passive 1-bit RISs. This method only requires a phase inversion operation (i.e., $0^{o}$ and $180^{o}$ phase states) for each RIS element. The algorithm is experimentally validated using a commercial RIS operating at 3.5 GHz in a mid-field anechoic measurement setup, (i.e., with a measurement distance much smaller than the Fraunhofer far-field distance of the RIS) demonstrating its effectiveness and robustness in practical setups.