The Curious Case of Effective Isotropic Sensitivity: Polarization mismatch in over-the-air testing of wireless user equipment

This article provides the theory behind the two-step over-the-air (OTA) test method widely used in 3rd Generation Partnership Project (3GPP) test specifications and, in particular, the testing and characterization of 5G millimeter-wave user equipment (UE) in compact antenna test ranges (CATRs). Special attention is paid to receiver (Rx) characteristics and the polarization mismatch problem, which is encountered in spherical coverage tests. The received power of a UE with a dual-polarized antenna system is derived, and the output signal-to-noise ratio (SNR) is calculated using the maximal ratio combining (MRC) principle. And finally, flaws in the dominant interpretation of this test method in the development of 5G millimeter-wave standards and their consequences are addressed.