This paper proposes three key antenna technologies in MU-MIMO transmission. First, the outdoor measurement results are shown by orthogonal polarization and patterns. We clarify that a simplified antenna selection can offer high channel capacity. Further channel capacity improvement is next achieved by adopting the radiation pattern optimization method. The bidirectional Yagi-Uda array is effective in providing fairly high channel capacity even when the terminal antenna is small. Finally, the short range MIMO transmission was introduced. It is found that there is an antenna spacing, which gives the maximum channel capacity. It is indicated that the optimal spacing can provide deterministically higher channel capacity than ergodic capacity of the i.i.d. channel.
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