Compact High-isolation UWB-MIMO Antennas For Mobile Terminals

Improving the data transmission rate and the information capacity, as well as the quality of service of wireless communications is the constant pursuit. With the development of technology, it is hard to achieve the goal with the traditional communication technology. Consequently, various kinds of new techniques emerge continuously. Among them, ultra-wideband(UWB) technology and multi-input multi-output(MIMO) technology, which have their own advantages and disadvantages, are two important methods to achieve the target. In order to effectively improve the information transmission rate and increase the channel capacity, the technology combining the characteristics of UWB and MIMO has been researched. For this purpose, high performance UWB-MIMO antenna is indispensable.To integrate multiple ultra-wideband antenna elements in a space limited mobile platform, the problem of UWB-MIMO antenna miniaturization and high isolation must be solved. In this thesis, we propose several high isolation miniaturized UWB-MIMO antennas.First of all, the arragement of UWB planar monopole antenna elements is studied. Parallel and orthogonal arrangements of two elements and parallel mirroring arrangement of four elements are investigated by electromagnetic simulations. In order to improve the low isolation between two close parallel UWB elements, an inverted T-shaped isolation structure is designed, which makes the antenna maintain good ultra wideband impedance matching and isolation characteristics. Within the band of 2.3-12 GHz, the reflection coefficient is less than-10 dB, and the isolation is higher than 20 dB, which improves 9 dB. Some monopole UWB-MIMO antennas are fabricated and measured. The S parameters, radiation pattern, efficiency, and envelope correlation coefficient are investigated.Secondly, dual-polarized UWB antenna is studied. The antenna element is designed, furthermore, a four-element dual-polarized UWB-MIMO antenna is proposed. In order to achieve a compact structure, a planar wide-slot antenna is used as the UWB antenna element. The UWB element is fed by two orthogonally placed coplanar waveguide ports, exciting orthogonal polarization modes. The element operates within the band from 3.4 to 11.7 GHz, and the isolation reaches more than 15 d B. Furthermore, the dual polarized UWB antenna element is used to design a compact four-element(eight-port) dual polarized UWB-MIMO antenna. By selecting a reasonable distance between elements, the matching and isolation of the multiple-element UWB-MIMO antenna are the same as the single UWB antenna element, while the port isolation between different elements reaches more than 20 dB. By simulations and measurements, the S parameters, radiation pattern, efficiency, and envelope correlation coefficient are investigated. Results indicate that this antenna has very good performance, and can be applied in practical UWB-MIMO communications.Finally, the work in this thesis is summarized and the future work is prospected.