A novel, compact multiple-input-multiple-output (MIMO) antenna design, occupying a mere 25 × 39 mm², is proposed for ultra-wideband (UWB) applications. This innovative antenna comprises dual square-shaped radiating elements and a modified T-shaped stub, incorporating a vertical slot to mitigate mutual coupling. Key performance metrics, including impedance matching, inter-port mutual coupling, voltage standing wave ratio (VSWR) and correlation coefficient, are scrutinized. Simulation outcomes reveal an impressive impedance bandwidth spanning 2.5 to 11.8 GHz (S₁₁ ≤-10 dB), accompanied by an exceptionally low envelope correlation coefficient (<0.002) across the entire frequency spectrum. Notably, inter-element isolation exceeds-23 dB throughout the operational band. The proposed UWB MIMO antenna efficiently covers prominent frequency bands, encompassing WCDMA, WLAN, WiMax and UWB, making it an attractive solution for multi-standard wireless communication systems.