This paper presents the design, simulation, and evaluation of a low-profile Multiple-Input Multiple-Output (MIMO) antenna configuration, optimized to meet the evolving demands of modernized wireless communication systems, incorporating LTE-Advanced (LTE-A) and emerging 5G Internet of Things (5G-IoT) applications. The antenna’s geometry relies on a novel design comprising staircase-shaped rectangular radiating patches with an integrated stub. This configuration is employed to improve impedance bandwidth and strengthen the isolation between antenna components, which are critical parameters in MIMO system performance. The antenna is fabricated on a Rogers RT/Duroid 5880 substrate, distinguished by its low dielectric loss and high-frequency stability. With a compact physical footprint of 96 × 96 mm2, the proposed design effectively serves the feature of integration into portable and space-constrained wireless devices. The antenna operates effectively across frequency range of 2.13 GHz to 4.2 GHz, covering a broadband that encompasses multiple wireless communication bands, including sub-6 GHz 5G spectrum. Comprehensive performance evaluation was conducted using key MIMO metrics. The design achieves an Envelope Correlation Coefficient (ECC) of less than 0.015, indicating excellent diversity performance. The Mean Effective Gain (MEG) remains below -3 dB for all elements, while the Diversity Gain (DG) reaches up to 10 dB, supporting reliable signal reception in multipath environments. Furthermore, Channel Capacity Loss (CCL) is maintained below 0.12 bps/Hz, confirming the antenna’s proficiency in supporting fast data transmission rates with minimal degradation in channel capacity. Overall, the proposed MIMO monopole antenna exhibits a well-balanced trade-off between compactness, bandwidth, and isolation, making it a strong candidate for next-generation wireless platforms where high-performance, compact antennas are essential.