n that the element 742 Chapter 5 Figure 5.32 64-Element planar antenna array and mutual coupling between array elements [18]. Ideal conditions Uniform linear array Uniform square array + AAS Uniform square array Uniform linear array Antenna spacing (a) Figure 5.33 Network capacity as a function of mutual coupling in two antenna arrays [20]. spacing between elements on a 2D planner array needs to be three times greater than that between elements on a uniform linear array to maintain the same network capacity. A large antenna array to implement massive MIMO in both sub-6 GHz and mmWave frequency ranges does not provide antenna connectors due to added complexity and cost, physical size limitations, and resulting insertion loss. Consequently, the OTA tests are required. The OTA tests measuring the 3D antenna pattern can be performed either in the near-field or in the far-field. The measurements in the antenna near-field allow smaller anechoic chambers for the measurement; however, it requires an additional near-field to far-field transformation for antenna gain patterns. New Radio Access RF and Transceiver Design Considerations 743 As we mentioned in the previous sections, the OTA measurements can be used in pre- production and post-production phases. In the pre-production phase, the following OTA measurements need to be conducted [18]: Gain patterns: Gain patterns are either 2D from one of the three principal planes (E1, E2, or H-plane) or a complete 3D pattern. For antenna arrays with one or more beams, the 3D gain pattern is more useful. Radiated power: The EIRP is used to measure an AAS either as a UE or a BS. For UE testing, TRP is used instead where TRP is the weighted integral of the effective radiated power values over a sphere. Receiver sensitivity: Receiver sensitivity is characterized by the equivalent isotropic sensitivity (EIS) and measures the block error rate as a function of the receive power equal to the specified receiver sensitivity. Transceiver and receiver characterization: Each individual transc