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In this paper, a design of a closely‐coupled wideband multiple‐input–multiple‐output (MIMO) antenna using a new simple wideband decoupling circuit (DCkt) based on a 2nd order filter for isolation improvement is presented to decouple the wideband MIMO antenna array. The wideband closely‐coupled MIMO antenna and the DCkt are designed using the structure's admittance parameter. To achieve good isolation in wide‐bandwidth six hexagonal split‐ring resonators are utilized. The presented closely‐coupled wideband MIMO antenna is resonating at 5.08–6.30 GHz (WLAN) bands, with measured isolation (>25 dB) in the 5.12–5.98 GHz frequency range. The envelope correlation coefficient is less than 0.1, and channel capacity loss (Closs) is less than 0.05, along with good radiation characteristics. It exhibits an exceptional expansion that makes the proposed solution the right candidate for advanced technological applications such as 5G and IoT.

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This study proposes a new design approach for a dual‐band full‐duplex antenna to achieve high interport isolation using the differential fed technique. It consists of a single radiating patch, a differential fedline, and a direct fedline. A slotline‐based balun is used in the design to implement the differential fed, which offers minimum phase and magnitude imbalances to the patch of the antenna. The differential fed and direct‐fed lines are orthogonally connected to the radiating patch to realize dual polarization. Both the dual‐polarization and differential fed techniques help to improve the interport isolation of the antenna. It offers an interport isolation of more than 51 and 53 dB over the entire lower and higher operating bands, resonating at 3.22 and 4.1 GHz with 84 and 110 MHz bandwidths. To validate the proposed antenna, a prototype has been fabricated on an FR‐4 substrate with the dimensions of (1.79 × 1.79 × 0.017)λg (λg is the guided wavelength in the substrate at the lower frequency f1), with measured results consistent well with simulations. The far‐field measurement exhibits that the proposed antenna provides a unidirectional broadside radiation pattern and achieves a minimum cross‐polarization of less than −38 dB in all directions and less than −42 dB in the direction of the main lobe in both E‐ and H‐planes at the resonant frequencies. The antenna has insignificant backward radiation with the front‐to‐back ratio bold-italic≥ ${\boldsymbol{\ge }}$20 dB when port1 is active and the front‐to‐back ratio bold-italic≥ ${\boldsymbol{\ge }}$30 dB when port2 is active. Moreover, the proposed antenna design is simple and easy to fabricate as the differential fed is implemented using the slotline‐based balun within the same general purpose FR‐4 substrate layer. This eliminates the need for any additional and separate circuits for differential fed and minimizes the overall volume of the antenna.

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