 are defined for each RF characteristic at an individual or a group of TAB connectors. The con- ducted requirements are defined such that they are equivalent to the corresponding conducted requirement of a non-AAS BS, which implies that the performance of the system or the impact on other systems is expected to be the same. Radiated requirements, on the other hand, are defined based on OTA measurements conducted in the far-field of the antenna sys- tem. Since the spatial direction becomes relevant in this case, it is detailed for each require- ment how it applies. The radiated requirements are defined with reference to a radiated interface boundary (RIB) in the far-field region of the antenna array [5,10]. 666 Chapter 5 Transceiver array boundary Radiated interface boundary (RIB) Transceiver unit array (TRXUA) 1 to M Transceiver unit 1 Radio Antenna Transceiver unit 2 distribution network array Transceiver unit M Composite antenna Transceiver array boundary connector (TAB) Figure 5.4 Radiated and conducted reference points for BS type 1-H [5]. BS, Base station. Rayleigh region Fresnel region Fraunhofer region (reactive near field) (radiative near field) (far field) Antenna/ Antenna array d < 0.62 D3/2 d < 2D 12 d < 2D 2 Figure 5.5 Illustration of the radiation regions of an antenna element/array. In order to determine an appropriate point in the antenna array far-field region for conducting the OTA measurements, one must understand the radiation characteristics of the antenna sys- tems and be able to define the minimum distance dmin in the far-field radiation region of an antenna array. In the theory of electromagnetics and antennas, the radiation regions surround- ing an antenna element/array can be divided into three regions as follows (see Fig. 5.5): Reactive near-field region: In the immediate vicinity of the antenna, we have the reac- tive near-field. In this region, the fields are predominately reactive fields, which means the electric (E) and the magnetic (H) fields are out of phase by 90 degrees relative 