ent require different measurement and verification methods, thereby using various approaches to measure a massive MIMO system will require different test interfaces to both the complete antenna array and indi- vidual antenna elements. Antenna arrays with 64 or more elements (corresponding to an 8 X 8 cross-polarized antenna array) may not provide any individual antenna connectors in the final assembly. In earlier phases of the product design, however, antenna elements are typically accessible with connectors to verify the S-parameters of individual antennas. Verification and qualification of antenna arrays is required in all product development phases from initial R&D design to final production test. Mutual coupling between antenna elements has an adverse effect on network capacity. Therefore, simultaneous multi-port passive (conducted) measurements for accurate characterization are required [18]. In the design phase, when antenna connectors are still accessible, a vector network analyzer can be used to measure the mutual coupling between the antenna array elements. For antenna arrays, the most common measurement with a vector network analyzer is the S- parameter measurements (both transmission and reflection coefficients). The S-parameters include magnitude and phase information, which can be used to measure both near-field and far-field quantities. For a two-port system, S11 represents the reflection coefficient (reflected power at antenna 1 divided by injected power at antenna 1) and S21 denotes trans- mission coefficient (transmitted power at antenna 2 divided by injected power at antenna 1). An example of an antenna array is shown in Fig. 5.32 with 64 dual-polarized antennas and 128 antenna ports. Due to the large number of antenna ports, connecting cables and subse- quent calibration of the vector network analyzer is difficult and time-consuming [18]. Fig. 5.33 illustrates the effect of antenna mutual coupling on the capacity of the cell. We compare a uniform linear array with a 2D planner array. It is show