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Researchers at Tsinghua University have taken a 3D approach to MIMO antennas and have built a 2.4 GHz MIMO antenna for WLAN applications that is much smaller than previous designs but still has high isolation and good omnidirectional coverage. The spectrum efficiency and transmission quality of wireless communication systems are improved through the use of multiple antennas at both the transmit and receive ends. MIMO antennas are being widely researched at the moment as they enable the use of the spatial degree of freedom in a wireless multipath channel, and they form a key technology for future wireless communication systems such as 3GPP, LTE, WiMAX 802.16, IEEE 802.20 and IMT-Advanced. At the moment MIMO antennas are only adopted in some large static base stations. This is because in these space-separated antenna arrays, nearly half of the wavelength is needed to achieve acceptable isolation; about 15 dB for most situations. In modern communication systems, the space is limited in both the base stations and the mobile terminals, and as the antennas shrink in size, the mutual coupling between the elements increasingly restricts the performance. The design of antennas for a space-limited MIMO system is therefore still a challenge.