Midfield Over-the-Air Test: A New OTA RF Performance Test Method for 5G Massive MIMO Devices

5G massive MIMO devices require over-the-air (OTA) calibration and RF measurement in a phase coherent test system. Device and antenna array size make it very challenging to measure RF performance in a true far-field OTA environment due to the large distances required, which also impact the link budget and test system cost. This paper presents a millimeter-wave (mmWave) midfield (MF) OTA RF performance test system designed to minimize size and cost. This system can perform antenna array phase coherence calibration and support RF parametric measurement per 3GPP conformance test specifications. An overview of system design challenges and measurement approaches is provided. Detailed theoretical analysis and simulation of the MF OTA test method are provided, together with experimental validation of the system's performance to prove its effectiveness in OTA phase coherence calibration and in RF parametric measurement for 5G massive MIMO devices.