This chapter presents a novel mutual coupling reduction technique for wideband multiple-input–multiple-output (MIMO) antennas in a parallel configuration. The approach is based on ground plane alterations. Here, n-section rectangular slits below the feed line are considered and analyzed the effect of multiple sections on achievable isolation levels. A benchmark set of four wideband MIMO antennas is utilized to examine the actual impact of the considered alterations on radiator isolation. Rigorous numerical optimization of all geometry parameters is carried out to ensure the minimum size of the structures while satisfying two performance constraints: reflection |S11|≤−10 dB and isolation |S21|≤−20 dB, both within the operational bandwidth. Other performance figures obtained for the considered antennas such as Envelop Coefficient Correlation (ECC < 0.005), diversity gain (DG > 9.99 dB), and total efficiency approximately >80% also demonstrate that high isolation is achieved without compromising the important MIMO antenna characteristics. Numerical results are verified experimentally. The effects of the user’s hand on the antenna performance are also investigated through full-wave EM analysis using the standard human phantom.