Electromagnetic waves can not propagate in the structure called electromagnetic energy gap (EBG) in the operating band. High impedance surface or artificial magnetic conductor is one kind of the EBG structure. HIS can suppress the surface current so it can be used to improve isolation in MIMO antennas system. This technique presents multi-bands EBG structure to improve isolation and to reduce distance between antennas. The presented sample 4x4 MIMO antennas system whose size is 87.6x87.6x3.2 mm^3. The multi-band EBG structure covers WiFi-2.4/5.2/5.8 GHz bnads.

This technique presented the MIMO antennas combined a EBG structure. Therefore, the isolation between antennas improves and the distance between antenna reduces. The area of the single antenna is 43.8 x 43.8 mm^2(~0.35 wavelength@2.4 GHz). The MIMO antennas can be combined arbitrary as  a 2x2, 4x4,...MIMO antennas system by the single antenna. The MIMO antenna system can be mounted any walls or metal surfaces, because of the EBG structure behind the MIMO antenna.

The MIMO antennas places before the EBG structure. The overall thickness is 3.2 mm. The radiation pattern of the MIMO antennas, which covers whole WLAN bnads, is directional. Therefore, this MIMO antenna can be used in wireless router. The MIMO antenna can be mounted on any walls and metal surface because of the EBG structure behind the MIMO antenna.