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In this letter, a compact ultrawideband (UWB) multi‐input‐multi‐output (MIMO) antenna with cross‐shaped unconnected Ground stub using characteristic mode analysis (CMA) is presented. The proposed work consists of two elliptical shape monopole UWB antenna with a cross‐shaped stub in the ground plane. The compact MIMO antenna has the dimension of 25 × 25 × 1.6 mm3. These monopoles are able to excite several characteristic modes (CMs), which support to wideband resonance, and cross‐shaped stub support CM at lower frequency band in the ground plane and reduces mutual coupling between monopoles. The UWB MIMO antenna is resonating in frequency bands from 2.97 to 13.8 GHz bandwidth with a good mutual coupling (<−15 dB). The diversity performance envelop correlation coefficient (ECC) and diversity gain (DG) of the antenna are less than 0.05 and more than 9.97, respectively. The experimental result confirming a good treaty with the simulated ones, so that the proposed antenna is suitable for compact UWB MIMO applications.

Here, a near‐zero permittivity (ε) and permeability (μ) metamaterial superstrate is presented as a decoupling structure for a multiple‐input–multiple‐output (MIMO) antenna. The proposed design offers peak isolation of 41 dB with reduced edge separation of 0.042λo at the resonating frequency. To verify the simulation results, the prototype of the proposed superstrate and antenna is fabricated and tested. The two‐element MIMO antenna has −10 dB impedance band of 5.5–5.92 GHz with a peak measured gain of 7.41 dBi and efficiency above 78%. The measurement results ensure an isolation enhancement of 30 dB with a correlation coefficient of <0.26 within the operating band. The proposed method offers a good design technique for high gain and a closely packed MIMO antenna system for WLAN applications.

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