Research On Dual-polarized Pattern Reconfigurable Antennas For LTE Application

In the 21 st century, with the rapid development of technology and economy, mobile communication technology has also been rapidly developed. From the second generation mobile communications networks in the 1990 s, such as GSM and CDMA, to the third generation mobile communication networks, such as WCDMA, TD-SCDMA and CDMA2000, then to the recent commercial trial LTE(Long Term Evolution), higher channel capacity and better signal quality are required. As the indispensible components for the signal transmission and receiving, antennas must meet the challenge of the continuing development of wireless communication systems.To increase the system capacity and improve the signal quality, base station antennas of the wireless communication system are required to obtain ± 45°dual linear-polarization characteristic. If the radiation beam of the antenna can be changed according to the user’s location, it is more conducive to improve the signal quality. These requirements have also brought new challenges to the antenna design. ± 45° dual linear-polarization antennas have been widely used in the mobile communication systems, but most pattern reconfigurable antennas are still in laboratory research stage, and have a distance to the application of the mobile communications. For the pattern reconfigurable antennas, the patterns are typically reconfigured by controlling the adjustable elements installed on the antennas. Thus with fewer antennas, without complex algorithms and expensive phase shifters, the radiation patterns can be adjusted. In the thesis, a pattern reconfigurable antenna is combined with the dual linear-polarization antenna effectively, and the dual linear-polarization pattern reconfigurable microstrip antenna is studied, which meets the requirements of the new communication systems. The research has high theoretical and engineering value.The thesis contains the following work:The first chapter introduces the background and significance of the subject, including the LTE introduction, reconfigurable antennas research status, and dual-polarized antennas research status.The second chapter introduces the antenna and microwave circuit theory, which is used in the antenna design, including the microstrip antenna, Yagi patch antenna, dual-polarized antenna, matching stubs and multi-section impedance transformer for the broadband matching, etc.The third chapter introduces the design of a dual linear-polarization pattern reconfigurable microstrip patch antenna, which meets the bandwidth requirement. Based on the principle of Yagi antenna, the pattern reconfigurable antenna achieves four operation modes by controlling the switches installed on the ground plane. The antenna achieves the bandwidth of 200 MHz at 3.5 GHz. At the same time, the isolation between the two ports is higher than 19 dB. Besides, good cross polarization discrimination performance is obtained. Two reconfigurable antennas work at 3.5 GHz and 2.4 GHz respectively are designed in the same method, in order to summarize the design method.In Chapter IV, the antenna works at 3.5 GHz is fabricated and measured, and the results of the simulation and measurement are compared. The reason of the inconsistence between the simulation and measurement is analyzed, and the improvement proposal to reduce the fabrication and measurement error is suggested.The last chapter summarizes the whole thesis and the future work outlooks.