Correlation of hybrid beamforming arrays in the context of OTA testing

Hybrid beamforming antenna arrays are a prominent component in communications at mm-wave frequencies. Multiple analogue beamforming arrays will be used for spatial multiplexing of signals also in hand held devices. In this work we derive the correlation coefficient for signals received by two ideal arrays in simple power angular distribution schemes. The purpose is to develop tools for evaluating over-the-air setups for testing of hybrid beamforming devices. We show a few exemplary correlation error evaluations that compare near field multi-probe OTA setups with a perfect target channel model. Results indicate that the correlation error increases with decreasing range length and channel angular spread. Moreover, larger inter-array spacing and sub-array sizes increase the correlation error.