Conventional communication systems have the limit of capacity due to the limit of the average spectral efficiency [1]. Multiple Input Multiple Output (MIMO) systems have been believed to overcome the limits of SISO channel capacity [2]. In this system, multiple antennas used at the transmitter and the receiver can receive multipath signals in parallel. This new perspective actually uses the multipath to increase diversity gain, thus providing increased data rates. Also, level of signals is robust through space-time signal processing. For this reason, MIMO is considered as the future system. For non-MIMO system, or conventional system, capacity is not affected by correlation of signals since single antenna is used. Challenge of implementing of MIMO systems is that correlation of signals at nearby locations makes the capacity decrease. Thus, to design MIMO antenna, it is necessary to study the behavior of the correlation. This is the main study of this thesis. First, the thesis presents the evaluation of 2$\times$2 MIMO system in 2.6 GHz using the standardized 3GPP/3GPP2 Spatial Channel Model (SCM) [17]. The author attempts to study the behavior of correlation as function of antenna orientation, polarization, spacing, configuration and environment scenarios. Second, thesis presents the evaluation of MIMO performance in reverberation chamber, which is considered to be rich multipath environment. Results show that capacity varies insignificantly with spacing of antenna elements. Third, the author derives and analyzes the spatial correlation in case of flat fading environment. The results indicate that spatial correlation is very sensitive to the orthogonality of pattern and polarization and varies insignificantly with XPD. Finally, the author designs and fabricates a polarized MIMO antenna array in 2.6 GHz. The array composes of one printed dipole having vertical polarization and one Alford-loop antenna having horizontal polarization. And evaluation of the antenna array was made in term of spatial correlation. The results show that the correlation of the antenna array is very low and can be used for MIMO system.
