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Multiple-input multiple-output (MIMO) antennas with four and eight elements having connected grounds are designed for ultra-wideband applications. Careful optimization of the lines connecting the grounds leads to reduced mutual coupling amongst the radiating patches. The proposed antenna has a modified substrate geometry and comprises a circular arc-shaped conductive element on the top with the modified ground plane geometry. Polarization diversity and isolation are achieved by replicating the elements orthogonally forming a plus shape antenna structure. The modified ground plane consists of an inverted L strip and semi ellipse slot over the partial ground that helps the antenna in achieving effective wide bandwidth spanning from (117.91%) 2.84–11 GHz. Both 4/8-port antenna achieves a size of 0.61 λ × 0.61 λ mm2 (lowest frequency) where 4-port antenna is printed on FR4 substrate. The 4-port UWB MIMO antenna attains wide impedance bandwidth, Omni-directional pattern, isolation &gt, 15 dB, ECC &lt, 0.015, and average gain &gt, 4.5 dB making the MIMO antenna suitable for portable UWB applications. Four element antenna structure is further extended to 8-element configuration with the connected ground where the decent value of IBW, isolation, and ECC is achieved.

A novel compact structure of wrench-shaped MIMO antenna for ultra-wideband applications is presented in this paper. The acceptable return loss ( $\mathrm{S}11 \leq -10$ dB) values of the proposed layout ranging from 3.18 GHz to 11.15 GHz. Half circular slotted T shaped stub is used for isolation enhancement. The isolation ( $\vert \mathrm{S}21\vert$ ) between elements is higher than the 15 dB for the entire operating band and it is above 20 dB in mystifying the band The realized peak gain and efficiency values are 1.97-5.61 dB and 85-95% respectively. MIMO performance metrics checked with MEG (Mean effective gain), MEG ratio (MEG1/MEG2), ECC (Envelope correlation coefficient), DG (Diversity gain) and TARC (Total active reflection coefficient) values. The structure is designed and simulated on a low-cost FR4 substrate of size 24 × 32 × 1.6 mm3, constant 4.4 (€r) with loss tangent of 0.002.

A very compact and closely spaced circular-shaped UWB – MIMO antenna with slotted T-shaped stubs and protruded strips for high isolation is discussed in the present paper. The fractional bandwidth of the proposed model reaches 134.68% from 2.82 GHz to 14.45 GHz with S11