In this paper , two compact and small size 2 × 2 and 4 × 4 multiple-input-multiple-output (MIMO) antennas are designed and fabricated for ultra-wideband applications. Using the neutralization line technique, the mutual coupling between the radiating patches is highly reduced. The overall dimension of the proposed 2 × 2 and 4 × 4 UWB MIMO antennas are 21 × 34 × 1.6 mm 3 and 48 × 34 × 1.6 mm 3 , respectively. The measured bandwidth of 95.22% (3.51–9.89 GHz) and 96.47% (3.52–10.08 GHz) with better isolation of ≤–22 dB and ≤–23 dB for 2 port and 4 port antennas are, respectively, achieved. The measured (4 × 4 antenna) realized gain and radiation efficiency vary from 0.95 to 2.91 dB and from 70.01% to 79.87% respectively, throughout the entire frequency band. Moreover, the performance of 4 × 4 MIMO antenna, in terms of isolation, realized gain, radiation efficiency, envelope correlation coefficient (ECC), diversity gain (DG), mean effective gain (MEG), total active reflection coefficient (TARC), channel capacity loss (CCL) and radiation patterns are studied and corresponding results are validated with the measured results.