Mutual coupling between elements in compact transmit antenna arrays is taken into account in performance prediction and system design of multiple-input multi-output (MIMO) systems. The transmitter-end coupling matrix comprised of array impedance matrix and effective load impedance matrix is derived. The impact of transmitter-end mutual coupling on spatial correlation, radiated power, and system capacity is studied. It is shown that for MIMO systems with compact transmit antenna arrays, transmitter-end mutual coupling seriously degrades system capacity. To mitigate the capacity degradation, a simple transmitter-end coupling cancelation method is proposed. It is shown through numerical experiments that the proposed method can significantly improve system capacity in the case that transmit antennas are placed closely.