Abstract: With the aim of implementations in practical engineering, the multiple-input multiple-output (MIMO) systems are analyzed. In ideal MIMO systems where the sub-channels are independent mutually, the signals from transmitter antennas can be separated and then combined by employing joint detection (JD). However, in practice MIMO wireless environment, since the signals from transmitters are transmitted over the same carrier frequency, the sub-channels of MIMO systems are dependent, which results in that the JD technique is infeasible and the decrease of spectral efficiency. To overcome the problem, based on the analysis of both the Shannon theorem and the phase-controlled antenna array (PCA), a multiple-antenna system model is presented, which is referred to as SHPCA model. In the presented SHPCA model, the PCA technique is used perfectly to produce narrow directional radio beam with very higher power efficiency to form space division multiplexing (SDM), by which the performance of the multiple-antenna systems is improved greatly. At the same time, for the SHPCA model, we also present a novel engineering capacity formulation called 3-dimensional channel capacity formula (3DCC), in which the 3rd dimension is the space dimension. The presented 3DCC formulation indicates clearly the effect of the SMD and the equipments of antenna on the capacity of multiple-antenna.