The Research And Exploration Of Ground-Independent Antenna

With the growing importance of high speed train in transportation, people pay increasing attention to the wireless communication on the train. As an important part of wireless system, the performance of antenna has a great influence on the quality of communication. When applying the antenna to a train which have different size of carriages or even different trains, the work frequency of antenna will shift, because of the ground-reliance. This situation brings trouble to installation and production. In order to avoid this problem, it is necessary to study how to reduce the ground-reliance of antenna.As we all know, the photonic bandgap structure can improve the performance of antenna. On the basis of studying the high-impedance ground plane, this thesis designs a ground-independent antenna. The design details and test results are given. The results show that the ground-reliance of antenna is reduced by using the high-impedance ground plane. This design provides a new idea of antenna for railway communication.According to the trend of multi-band sharing in railway communication, the possibility about realizing a dual-frequency high-impedance ground plane is studied. By combining two high-impedance ground planes which have different period, this thesis find a way to get a dual-frequency high-impedance ground plane. The performance of various structure combinations is researched. The physical samples are made and tested. The measured results are basically consistent with theoretical analysis. This design gives a foundation for reducing the ground-reliance of multi-band antennaThis paper is divided into five parts.Firstly, this paper introduces the background and present situation of the research, and points out the significance of the research. The foundation of further discuss is laid in this part.Secondly, some important parameters in the design of an antenna are introduced. Then, a vertical monopole antenna whose work frequency is 2.4GHz is realized. The design in this part is mainly prepared for the further study of ground-independent antenna.Thirdly, the ground-reliance of antenna is discussed. It is noticed that when the area of the metal ground plane changes, the work frequency of antenna is also changed. Then, the concept and the usage of high-impedance ground plane are introduced. The important structure parameters which influence the resonant frequency of the high-impedance ground plane are analyzed. After optimization, the parameters of high-impedance ground plane are gained. The simulation and measurement results show that high-impedance ground plane can reduce the ground-reliance of antenna effectively.Fourthly, a new type of dual-frequency high-impedance ground plane is proposed. The effect of dual-frequency is obtained by combining two different single-frequency high-impedance ground planes. The parameters which affect the S11 and resonant frequency are studied thoroughly, and the basic laws are summarized. The physical sample of dual-frequency high-impedance ground plane is made. The feasibility of the design is verified by measurement.Finally, the paper summarizes the whole work, the results shows that the high-impedance ground plane can reduce the ground-reliance of antenna. Especially, the rational distribution of dual-frequency high-impedance ground plane can reduce the ground-reliance of dual-frequency antenna. This research gives a reference for the design of railway wireless communication system.