Over-The-Air Tests of 5G Devices with Direct Measurements at Reduced Distance and Parallax Compensation

Over-the-Air (OTA) measurements of modern mmWave User Equipment (UE) should be performed under plane-wave conditions which require sufficiently large measurement distances. Alternatively, shorter distances can be considered but special plane-wave generator devices should be used instead of conventional probes/range antennas. The use of probes/range antennas at reduced distances would offer advantages in terms of cost effectiveness and improved dynamic range but in general, they would not provide the proper planewave condition. To set the proper measurement distance the electrical size of the whole UE is usually considered. However, in most cases only a smaller portion of the UE actively contributes to the radiation. Reduced distances can thus be considered without significant loss of accuracy, unless the source of radiation is offset from the center of the measurement system. This latter scenario is called parallax and often causes distortions of the pattern if the distance is not sufficiently large. In this paper parallax compensations techniques applicable to amplitude-only measurements will be investigated considering realistic OTA measurement emulations of modern devices equipped with mmWave phased arrays placed in different positions. The investigation is performed focusing both on the measurement of the single beams and on the overall spherical coverage provided by the antennas.