Studies On The Omnidirectional Antenna And Mimo Antenna Techniques In New Generation Wireless Mobile Communication

With the rapid development of new generation wireless mobile communication, especially with the growing popularity of 4G network, wireless indoor coverage occupies a pivotal position in communication system. With the deeper needs for information transmission efficiency, regional coverage, wide channel capacity and other aspects in wireless communication system, more stringent restrictions are proposed on bandwidth and dimensions of micro-base-station antennas. At the same time, LTE systems and dual-polarized MIMO antenna technology has been widely applied to mobile communication systems, in order to improve spectrum utilization efficiency and the quality of transmission and reception.Focused on the engineering requirements of omnidirectional-antenna for indoor ceiling network application, this thesis presents the studies on bandwidth improving and profile reducing of antennas on the premise of stable omnidirectional radiation patterns. The main contents and innovation points of this thesis are as follows:Firstly, the research background and significance of omnidirectional antennas for indoor ceiling networking system is presented. Meanwhile, a thorough overview of research status in recent years is given.Then, some key parameters for micro-base-station antennas are introduced briefly, and the design principles and application scenarios for indoor ceiling antennas in actual wireless mobile communications are presented.Thirdly, based on the ceiling antenna application environment, through the introduction of terminal capacitance loading shorted by four metallic pins to the ground, a modified vertically polarized(VP) omnidirectional antenna is designed with much lower profile and wider bandwidth(1710-2690MHz).Fourthly, this thesis proposed a novel horizontally polarized(HP), omnidirectional antenna, by using four arc dipoles laid in circular are combined to form a circular loop antenna. By the introduction of a tapered-balun and a series of parasitical strips, the antenna with better omnidirectional radiation patterns, wider bandwidth and lower VSWR is realized. Measured and simulation results of the proposed antenna show that the horizontally loop antenna obtains a lower VSWR<1.5 within the band of 1710-2690 MHz.Fifthly, considering the influence of application environment of a larger ground plane, artificial magnetic conductor structure(AMC) is introduced to the proposed horizontally polarized loop antenna. Measured and simulation results show that the overall height of loop antenna backed by AMC reflector is only 26mm(including a 2mm thickness of ground plane). Moreover, the designed antenna has very good antenna characteristics over 1710-2690 MHz.Finally, based on the previously designed HP/VP omnidirectional antenna elements, a low profile wideband omnidirectional dual-polarized antenna backed by AMC reflector is proposed and designed, which is cater to the requirements of indoor wireless communication. Measured and simulation results show that overall height of proposed antenna is 30.6mm(including a 2mm metal reflector), covering the band of LTE. Compared to other reported designs, the proposed antenna has a much lower profile and is capable of covering the entire LTE band, thus making it more suitable for practical applications.