In this manuscript, a planar, uni-layer two-port multiple-input multiple-output (MIMO) antenna covering the n77/78/79 5G bands is presented. An elliptical-shaped artificial metamaterial structure is used as a decoupling structure to restrict surface current and improve isolation between MIMO antenna elements. The prospective MIMO antenna element is made up of a slotted monopole, 50-ohm feeding line, and a partial ground conductor. For miniaturization, an inverted T-shaped slot is loaded on the radiator of the unit cell. The effective material properties of the suggested ellipse-shaped artificial material are estimated to assess its metamaterial behavior. The proposed MIMO antenna operates from 3300 MHz to 5000 MHz, covering the n77/78/79 5G frequencies. The performance of the presented 5G MIMO antenna is validated using the CST Microwave Studio and Ansys HFSS EM tools.