A very compact triple band-notched multiple input multiple output antenna (MIMO) for ultra-wideband (UWB) communications is fabricated on a FR4 dielectric substrate having overall size of 18 x 21 x 0.8 mm3. The proposed antenna consists of two rectangular metal monopoles which are excited by 50-Ω microstrip lines on top of substrate, and a common protrude ground is at the bottom. To achieve low mutual coupling between radiating elements, a T-shaped stub is protruded from the ground plane. By etching two C-shaped slots on the radiating patches, band-notched functions at 5.15-6 GHz and 7.8-8.4 GHz are obtained. The third notch band from 3.3-3.7 GHz is realized by adding U-shaped metal strips to the ground. The measured and simulated results demonstrate that the proposed antenna offers good impedance bandwidth of |S11| ≤ -10 dB from 2.8-12.2 GHz covering whole UWB band except at the designed notch bands, while giving less mutual coupling (|S21|) of lower than -25 dB in the whole UWB band. The measured envelope correlation coefficient (ECC < 0.013), nearly constant gain and stable radiation patterns show that the proposed MIMO antenna is an appropriate candidate for portable UWB systems.
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