Small footprint of the multi-input-multi-output (MIMO) antenna is extremely desirable for space-constrained ultra-wideband (UWB) communication systems. Compact MIMO antennas with improved isolation and wide operating bandwidth are the significant subject of the work. Therefore, this paper presents a miniaturized four-port polarization diversity UWB-MIMO antenna operating in the frequency range of 3.1-12 GHz with band-notched characteristics. Four octagon-shaped radiating elements with a common ground are placed orthogonal to each other for good isolation. Band rejection features between 4.5 and 5.5 GHz were achieved by including an open-ended slot at the upper edge of the octagon-shaped antenna. The MIMO antenna was etched on a low-cost 32.3 x 32.3 x 0.8 mm3 FR-4 dielectric substrate. The antenna radiates in a quasi-omnidirectional pattern on the H-plane throughout the operational bandwidth, with higher than 15 dB isolation, low envelope correlation, and high antenna gain. As a result, this antenna is well suited for diverse applications and portable devices.
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