This paper presents the design and simulation study of a compact four-port Multiple-Input Multiple-Output (MIMO) antenna with overall dimensions of 12×16×1 mm³. The design and full-wave electromagnetic analysis were performed using the High-Frequency Structure Simulator (HFSS). The antenna is comprised of four modified U-shaped radiating elements and an integrated claw-shaped parasitic element to achieve quad-band operation. The proposed design resonates at 2.5 GHz, 3.8 GHz, 5.4 GHz, and 6.9 GHz, covering key bands for Wi-Fi and 5G applications. Simulation results demonstrate good impedance matching, with a simulated return loss better than -10 dB at all target bands. The simulated peak gains are 1.8 dBi, 2.9 dBi, 3.95 dBi, and 4.45 dBi at 2.5 GHz, 3.8 GHz, 5.4 GHz, and 6.9 GHz, respectively. Furthermore, the MIMO performance is evaluated through simulation, showing a low simulated envelope correlation coefficient (ECC < 0.05) and high simulated diversity gain (DG > 9.95 dB), which confirms excellent channel isolation in simulation. Owing to its miniature size, simulated multi-band performance, and good simulated MIMO characteristics, the proposed antenna presents a promising