A multiple-input-multiple-output (MIMO) antenna with a built-in decoupling mechanism is proposed for wireless local area network (WLAN) 2.4/5 GHz dual-band operations. The antennas were printed on an FR4 substrate and were located at the top portion of the FR4 board. The size of the antenna is 20 × 11 mm. The MIMO antenna system consists of two parallel folded branch monopoles with coupled feeds configured as two sets of two off-centred circular pads; the smaller ones were connected to the feeds and the larger ones were connected to the branch antennas. The coupled feed was used to achieve broad impedance matching bands. The two coupled feeds, separated by a small gap, were found to exhibit a built-in isolation mechanism, due to the opposite currents generated at the feeds and at the edges of the circular pads. That is, no additional physical structure was necessary to facilitate the needed isolation. The measured results show that both antennas have good impedance matching and port isolation. The antenna port envelope correlation coefficient was less than about 0.2 over the dual 2.4/5 GHz bands.

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A simple single‐plate, π‐shaped multiple–input multiple‐output (MIMO) antenna with built‐in port isolation operated at 5 GHz (5150–5850 MHz) band is proposed. The MIMO antenna is a symmetrical structure formed on a single‐layered FR4 substrate. The main radiating element is of a single‐plate π‐shaped structure, and is 4 mm away from the antenna ground. The ground plane in this design provides sufficient finite size to properly excite the antenna. The π‐shaped structure has a few desired features: a space saver, due to co‐location of impedance matching network and isolation structure; built‐in isolation and stable MIMO operations; existence of stationary current sink and source (S‐S/S) points, which were proven to be the key to enhance port isolation. Since the commonly referred neutralisation line (NL) technique does not exhibit S‐S/S points; thus, our design is not considered as a NL. The radiation patterns of the two planar inverted F antenna ‐like monopoles cover the complementary space regions of 45°–50°, the antenna yields peak gain varied from 2 to 3 dBi, and radiation efficiency was >60% at 5 GHz band. The antenna port envelope correlation coefficient was about 0.05.