With the rapid development of wireless communication technology, ultra-wide band (UWB) communication offers advantages such as high transmission rates and large capacity. multiple-input multiple-output (MIMO) technology plays a crucial role in enhancing the performance of communication systems. This paper proposes a microstrip-fed ultra-wideband dual-notch MIMO antenna. By etching semi-elliptical notches on the circular radiating patch, ultra-wideband characteristics are achieved. A U-shaped slot is etched on the radiating patch to suppress interference from the 5G WiFi band (5.125~5.925 GHz), while an inverted U-shaped slot is etched on the feed line to reject interference from the Ku-band downlink standard frequency range (12.2~12.75 GHz). The design is validated and analyzed using characteristic mode theory The antenna consists of two unit antennas placed in parallel. The unit antennas are connected through a shared ground plane, and an L-shaped isolation stub is employed to effectively improve the isolation (｜S21｜) between the antennas. The antenna dimensions are 60 mm×30 mm×1 mm. Measurement results demonstrate that the antenna achieves an impressive -10 dB operating bandwidth of 3.88~20.49 GHz with a remarkable fractional bandwidth of 136.3%. The MIMO configuration exhibits excellent performance characteristics, including: port isolation greater than 20 dB across the entire operating band, a peak measured gain of 6.1 dB, envelope correlation coefficient (ECC) below 0.02, and diversity gain (DG) exceeding 9.99. These parameters confirm superior diversity performance and radiation characteristics. The proposed design shows significant potential for UWB-MIMO system applications, offering promising prospects for advancing wireless communication technologies and fostering innovation in this field.