Research On New MIMO Antenna Isolation Technology

Diverse mobile devices and abundant multimedia services require higher and higher information transfer rate in communication network, although conventional wireless communication systems could improve the spectral efficiency through better techniques and algorithms, the channel capacity of the system is still limited by frequency band lacking. As a key technology of the fourth-generation mobile communication system, MIMO technology can make use of signal fading and multiple signal paths caused by multipath environments to increase data throughput without occupying additional spectrum resources, and it can greatly improve the radio channel capacity, communication quality and the transmission distance. These advantages make MIMO technology more attractive in recent years. Compared with the space base stations, terminal devices take smaller spaces, so the design of UWB MIMO antennas which are smaller in size and with high isolation has become one of the key issues.In this paper, we designed two kinds of4-ports UWB MIMO antennas based on theoretical analysis and the previous work.The first proposed UWB MIMO antenna uses an embedded "U" shaped metal frame to improve the isolation between the MIMO units. The main radiating elements of this MIMO antenna consists of four vertically placed UWB microstrip antennas. With the "U" shaped frame embedded in the dielectric plate between the basic antenna elements, the isolation has greatly improved without increasing the antenna dimensions. This MIMO antenna is implemented on an FR4substrate, which has dielectric constant of4.6and thickness0.8mm, with the symmetric cross type structure and74.8mm main path. The proposed MIMO antenna reached the frequency band of3.2-12.6GHz with good perspective diversity gain characteristics, and the isolation degree between two antenna units are below-15dB over its working frequency band, isolation between the two antenna units located on the diagonal even gets-20dB lower.The second proposed UWB MIMO antenna uses a coupler with fences form "V" type structure to improve the isolation degree. Four basic antenna units and dielectric plate of this antenna has the same scheme with the first proposed antenna. The difference is that we printed the two radiating elements on the diagonal on the other side of the substrate, and the size of the dielectric plate is60mm x60mm. The coupler with "V" type structure is printed directly on the dielectric plate and lies between the vertically placed antenna units. Through the simulation modeling, this antenna reaches the working frequency band of3.13GHz-12.34GHz,the isolation degree between the two adjacent antenna units is below-15dB, while the isolation degree of the two antennas on the diagonal is below-20dB.