In this paper, we propose four elements proximity-coupled multi-input-multi-output (MIMO) micro-strip patch antenna working from 27 to 29.16 GHz for 28 GHz mm-wave 5G applications. We begin with the development of a single element, which is made of two layers of Rogers RT5880 substrate with a relative permittivity of 2.2. A parametric analysis, based on finite difference time domain analysis (FDTD), is conducted to boost the structure's performance. A quad-element arrangement is examined for the MIMO antenna. Additionally, the isolation is improved by using the spatial diversity approach, which achieves better than 24 dB of isolation over the targeted frequency spectrum. The envelope correlation coefficient (ECC) and the diversity gain (DG) are determined to be within acceptable bounds. The results indicate that the design is an interesting candidate for upcoming mm-wave 5G MIMO applications.