A MIMO antenna with built-in isolation for WLAN USB dongle applications

A novel couple-fed dual-bands MIMO antenna is proposed for WLAN 2.4/5.2/5.8 GHz bands. The MIMO antenna system consists of two parallel folded branch monopoles with an edge-to-edge separation of 0.2 mm. The antenna elements are printed on an FR4 substrate and are located at the top edge of the ground plane. Size of the antenna is 20 mm (W) × 11 mm (L). The isolation is achieved by introducing a round off-set structure at the end of the coupled feeding-line. Measured results show that antennas have good impedance matching and port isolation. Since we have not introduced any isolation enhancing structure, the MIMO antenna appeared to have a built-in decoupling mechanism. When one end was fed, the current distributions on the other feed line was reduced in magnitude by a self generated counter current occur at the round off-set structure area. That is, the self generated counter current has contributed the needed isolation between the two antennas. The results suggest that the proposed novel simple, compact antenna structure has indeed attained good isolation characteristics required for MIMO operations. Moreover, the antenna is easy to fabricate and suitable for applications at the 2.4/5.2/5.8-GHz bands.