Test Zone Characterization in RTS-Based MIMO Measurement Systems

Over-the-air measurements are essential for evaluating wireless transceivers, particularly in multiple-input multiple-output (MIMO) systems. However, the 3rd generation partnership project and the cellular telecommunications and internet association do not explicitly define the test zone characteristics for radiated two-stage (RTS) MIMO testing. This paper focuses on RTS MIMO testing, specifically examining the key factors that influence the test zone. We investigate the relationship between MIMO data stream isolation and signal reflection level, as well as reflection time delay, and analyze its performance across different bandwidths. The main novelty of this paper lies in systematic analysis and experimental validation of reflection-related test zone characteristics of RTS-Based MIMO measurement method for the first time. Unlike conventional quiet zone definitions that focus solely on reflection level, this work demonstrates that both reflection level and time delay must be jointly considered to ensure sufficient MIMO stream isolation. We show that even in small chambers, accurate RTS testing is possible if the reflection delay is short enough, offering a practical and cost-effective alternative to large, low-reflection environments. Additionally, a bandwidth-aware evaluation method is proposed, enabling early assessment of chamber suitability for RTS MIMO testing based on reflection parameters. This represents a significant advancement in the practical implementation and standardization of RTS-based OTA MIMO testing.