<p>This research employs double defected ground structures (DGS) and parasitic patches to enhance the overall performance of the multiple input multiple output (MIMO) antenna. The proposed MIMO antenna operates effectively within a frequency range of 5.5–6.5&#xa0;GHz. DGS 1 and DGS 2 are etched on the ground plane surface. Specifically, DGS 1 is located precisely beneath each feeding line in the four MIMO antenna elements. Additionally, DGS 2 is placed in the center of the ground plane. The parasitic patches are positioned on the same surface as the MIMO antenna’s radiating patches. The proposed MIMO antennas have an overall size of 82.4 × 82.4 × 1.67 mm³ and are made of FR4 substrate, which has a loss tangent (<i>tan δ</i>) of 0.022, a dielectric constant (<InlineEquation ID="IEq1"> <EquationSource Format="TEX">\({\varepsilon }_{r}\)</EquationSource> </InlineEquation>) of 4.3, and a thickness (<i>h</i>) of 1.6&#xa0;mm). Realization of the DGS 1, DGS 2, and parasitic patches improves the reflection and transmission coefficients. According to the simulated and measured results, the reflection coefficients are expressed as S₁₁, S₂₂, S₃₃, and S₄₄, indicating that the proposed MIMO antennas have a measured impedance bandwidth (IBW) (S₁₁ &lt; −10&#xa0;dB) of 1.05&#xa0;GHz. Transmission coefficients include S₁₂, S₁₃, S₁₄, S₂₃, S₂₄, and S₃₄. It presents a mutual coupling level among the four-element MIMO antenna. The measured mutual coupling results achieve a range of −32 to −52&#xa0;dB along the operational frequencies. Furthermore, additional diversity performance metrics, such as envelope correlation coefficient (ECC), diversity gain (DG), and mean effective gain (MEG), are examined. Utilizing S-parameters, the calculated values of ECC, DG, and MEG are less than 0.0035, exceed 9.992&#xa0;dB, and range from −6.2 to −8.5&#xa0;dB, respectively. The proposed MIMO antennas exhibit favourable specifications for MIMO systems in the C-band.</p>