| Combined with the related scientific research project, the quardrifilar helix antenna for Global Positioning System(GPS) is studied in this paper. With the development of technology and the popularity of application, people depends on the GPS system more and more in life, portable mobile navigation gets the favor of people. In order to meet the needs of people, the miniaturization navigation with high performance has become the research hot spot. Antenna is an important part of the receiving device in satellite positioning system, its performance affects the working status of the equipment directly. Antenna technology has become a key technology in the field of satellite communication research.Quadrifilar helix antenna has good radiation characteristics, it is very suitable as the terminal antennas of satellite navigation. In order to improve the integration of satellite navigation devices, some corresponding research works about the miniaturization technology of the quadrifilar helix antenna are done in this paper.The specific content studied in this paper is divided into two parts: 1.the design of dielectric-loaded quadrifilar helix antenna, 2.the design of wideband feed network with small size for the antenna feeding. This paper introduces the related theory and design method of the antenna and feed network in detail. The thesis is summarized as follow:Firstly, the development and research status of GPS is described briefly, and the structure characteristics of several common satellite terminal antennas are listed, including: quadrifilar helix antenna, microstrip antenna, cross dipole antenna, etc. By summarizing relevant literature, this paper introduces the history and progress of the quadrifilar helix antenna. Then the related theory of the helical antenna,the basic structure and the radiation mechanism of the quadrifilar helix antenna are introduced in detail, providing a theoretical basis for antenna design.Secondly, a small quadrifilar helix antenna working in the GPS L1 frequency band(1575.42MHz) is designed by using a ceramic dielectric column as the medium load which with a dielectric constant of 36.5. The polarization mode of this antenna is right-hand circular polarization. Compared with general antenna without medium load, the size of this antenna is very small: height is just 19 mm, screw diameter is about 10 mm. This paper gives the detailed design process of the antenna, and analyses the influence of antenna structure on the radiation characteristics. Based on the simulation model built in the electromagnetic software, the antenna sample is processed to test.Finally, a feed network with a working bandwidth of 1.2GHz~1.8GHz for quadrifilar helix antenna is designed, which combined with the 3d B directional coupler and 180 o hybrid junction. In order to reduce the overall size of feed network, the miniaturization design of directional coupler and hybrid junction are done in this paper. The 3d B directional coupler chooses broadside coupled stripline form, use folded spiral structure to reduce the volume and is buried among the LTCC substrates. The area of hybrid junction is reduced based on the fractal thought. This feed network has good amplitude responsion and phase balance, can help quadrifilar helix antenna to achieve good circular polarization characteristics. |
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