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Summary In this communication, a novel compact spanner shaped ultra‐wideband (UWB) antenna is designed for multiple input multiple output (MIMO) system applications. The proposed structure of size 24 × 32 mm2 (0.24λ0 × 0.32λ0, λ0 is calculated at lower band frequency) is designed and fabricated on widely available FR4 dielectric material with a dielectric constant of 4.4 and loss tangent of 0.02. The proposed structure comprises two spanner shaped antennas, a defected T‐shaped stub and a pair of small vertical strips. The defected T‐shaped stub and vertical strips are used for getting a complete UWB bandwidth and good isolation between two elements. It is performing from 3.0 to 11.0 GHz with isolation more than 20 dB in most of the operating region. The parametric studies have been done for the required parameters and figured out the surface current distribution at different resonant frequencies within the working region. The MIMO antenna diversity performance is confirmed with low values of envelope correlation coefficient (ECC < 0.005), channel capacity losses (CCL < 0.04 bits/s/Hz), acceptable mean effective gain (MEG ≤ −3 dB, MEG ratio = 0 dB), and total active reflection coefficient (TARC ≤ −10 dB) values. The peak gain values are varying from 1.5 to 6.0 dBi, and the radiation efficiency values are above 83% for the entire operating region. The simulated and measured values are well matched.

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 >15 dB, ECC < 0.015, and average gain >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.

This research reports a four-port multiple-input-multiple-output (MIMO) antenna designed for 5G-NR band applications including n77: 3.30–4.20 GHz, n78: 3.30–3.80 GHz, and n79: 4.40–5.00 GHz. The proposed design is analyzed in two parts, one single-element asymmetrical fed Calendula flower-shaped antenna and the other four-port modified MIMO antenna with the connected ground. The evolution of the MIMO antenna is studied based on the characteristics and optimized single-element antenna. The measured 5G-NR bandwidth offers a very high matching of impedance for MIMO configuration and higher isolation in the same band. The MIMO antenna offers an average peak gain of 3.51 dBi with a radiation efficiency of more than 90%. The radiation patterns plotted at 3.51, 4.00, 4.50, and 5.00 GHz match with almost omni-directional and dipole patterns in H- and E-radiating planes respectively. The MIMO antenna also records good diversity performance (ECC, DG, CCL, MEG, and TARC) in n77, n78, and n79 5G bands.