MIMO antenna design with built-in decoupling mechanism for WLAN dual-band applications

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.