Abstract: There are many application scenarios for the 5G millimeter wave band. The millimeter wave uses beamforming technology and needs to be implemented based on the antenna array. As the millimeter-wave RF front-end is highly integrated and generally does not have an RF test interface, almost all test cases have to be performed in an OTA(Over-the-Air) environment. Therefore, a reliable and stable test environment is a necessary condition to ensure accurate test results. However, the OTA system is a complex measurement environment composed of multiple parts such as an anechoic chamber, radio frequency cables, a positioner etc. Each part may introduce the corresponding measurement uncertainty and be transferred to the final measurement results. In addition, millimeter-wave measurement has the characteristics of high frequency and high loss, and it is more difficult to ensure the reliability of the measurement comparing system at relatively low frequencies. Therefore, the study of the uncertainty of millimeter-wave OTA systems is of great significance. This article describes and analyzes the uncertainty of the millimeter wave OTA system, and illustrates it with a typical 5G millimeter wave OTA measurement environment.

Key words: 5G, millimeter wave, OTA(Over-the-Air), uncertainty