Research Of Multi-Antennas Technology For LTE Terminals Based On Microstrip Antenna

Multi-antennas technology, typically known as multiple-input-multiple-output (MIMO) technology, is a key technology in wireless communication systems, and it can be used to improve the system capacity and reliability. There is a great deal of challenge for the application of MIMO technology on terminal devices, and there are still lots of problems have to be resolved. It can be say that research efforts on this subject play important roles on the development of the whole communication industry and the progress of investigating in the future wireless communication systems based on MIMO technology. The terminal devices are important parts of the communication systems, therefore, research of multi-antennas technology for mobile terminals is of great significance, and is also important to achieve the superiority of MIMO systems. In this thesis, the research content includes two aspects. First of all, studies on the influence of antenna parameters of the mobile terminals on the performance of MIMO systems are presented. Then two kinds of MIMO antenna based on microstrip patch antenna are proposed, and it should be noted that, in this section, the research efforts on MIMO antenna mainly focus on size reduction, wideband or multiband, of the microstrip patch antenna, as well as high isolation between antenna elements. The main work and achievements of this thesis are summarized as follows,1. An analytical approach of studying the influence of antenna parameters on the performance of MIMO systems is proposed. The antenna parameters in terms of isolation, envelope correlation coefficients and antenna gain imbalance are introduced first, and the derivation of the corresponding expressions are given. Then influence of these parameters on the capacity and diversity performance of MIMO systems are studied by channel modeling, respectively. At last, the influence of antenna gain imbalance, and isolation on the system throughput, and the influence of antenna correlation on the diversity gain are discussed respectively through a long term evolution (LTE) link-level simulation platform.2. A compact and dual-band microstrip MIMO antenna for LTE terminals application is proposed. The proposed antenna has a compact structure, and size reduction almost20%is achieved for single patch. The operation frequencies cover LTE band2570～2620MHz and3600～3800MHz, in which the isolation between two antenna elements is more than20dB and16dB, respectively. In addition, the performance of MIMO system consists of the proposed antenna is verified.3. A wideband circularly polarized microstrip MIMO antenna for LTE systems is proposed. By designing a wideband feed network (WFN) which composes of the coupled-line Wilkinson power divider and improved90°phase shifter, and utilizing the dual-feed structure, the proposed antenna achieves an impedance bandwidth of46%from1.85to2.95GHz for S11<-15dB, and3-dB axial ratio (AR) bandwidth of40%from1.9to2.85GHz. Additionally, orthogonal circular polarization of the two antenna elements for polarization diversity is employed.