radia- tion efficiency of small antennas and radiated power of mobile terminals could be measured with an accuracy of 0.5-dB RMS (root mean square) [27] in a small reverberation chamber. This was carefully validated by comparison with measure- ments in anechoic chambers [28] and larger reverberation chambers [27]. The reverberation chamber generates a Rayleigh distribution. Therefore, the chamber is particularly well suited for characterizing antenna and terminal functions specific for such environments, as described in Kildal and Rosengren [29]. Actually, the radiation patterns play no role in such environments because many interfering waves contribute to a statistical wave channel. The characterizing parameter is, for single-port antennas, the classical radiation efficiency, including contributions from mismatch, ohmic losses in nonperfect materials of the antenna and terminal itself, and losses in nearby objects such as a user's hand or head. It is important to note that these quantities will be the same as when they were measured in a "free space" environment like an anechoic chamber. Even the antenna impedance mea- sured in the reverberation chamber will appear the same as when it is measured in free space, after the processing of the complex S-parameters acquired over all stirrer positions [18]. Future terminals will, to higher degree, make use of antenna diversity to remove the problems of fading dips where the terminal may not work (i.e., outage), and the corresponding diversity gain (or, in other terms, reduction in outage probability) can directly be measured by reverberation chamber tests when evaluating the multiport antennas themselves [30,31] and when diversity is imple- mented in active mobile terminals [32]. The future mobile communication systems could make use of multiport anten- nas with even more advanced functions than antenna diversity for both uplink and downlink (i.e., MIMO antenna systems). MIMO antenna systems are character- ized in terms of the maximum available capacity, which also can