Mutual coupling reduction or isolation enhancement in antenna arrays is an important area of research as it severely affects the performance of an antenna. In this paper, a new type of compact and highly isolated Multiple-Input-Multiple-Output (MIMO) antenna for ultra-wideband (UWB) applications is presented. The design consists of four radiators that are orthogonally positioned and confined to a compact 40 × 40 × 0.8 mm³ space. The final antenna design uses an inverted L shape partial ground to produce an acceptable reflection coefficient (S11 < −10 dB) in an entire UWB band (3.1–10.6) giga hertz (GHz). Moreover, the inter-element isolation has also been enhanced to >20 db for majority of the UWB band. The antenna was fabricated and tested with the vector network analyzer (VNA) and in an anechoic chamber for scattering parameters and radiation patterns. Furthermore, different MIMO diversity performance metrics are also measured to validate the proposed model. The simulation results and the experimental results from the constructed model agree quite well. The proposed antenna is compared with similar designs in recently published literature for various performance metrics. Because of its low envelope correlation coefficient (ECC < 0.1), high diversity gain (DG > 9.99 dB), peak gain of 4.6 dB, reduced channel capacity loss (CCL < 0.4 b/s/Hz), and average radiation efficiency of over 85%, the proposed MIMO antenna is ideally suited for practical UWB applications.