| Global Positioning System(GPS) is one of the most widely used satallite navigation and positioning system, which mainly applied in a variety of fields such as navigation, mapping, monitoring, time distribution, communication and so on. Recently, GPS technology has been developed enormously in civil use, especially in vehicle navigation and personal mobile terminal positioning, which two are quite demanding of the miniaturization of antennas obviously. Among all the antennas, quadrifilar helix antenna is the ideal receiving antenna for GPS owing to the advantages of cardioid shaped pattern, good front-to-back ratio and excellent circular polarization.In this dissertation, we summarize the development and research conditions of quadrifilar helix antenna, and analyse its structure, working principle and performance characteristics. Besides, we design and fabricate a Miniature dielectrically-loaded quadrifilar helix Antenna. This kind of antenna, loaded by ceramic dielectric with high permittivity, with good performance while the volume shrinks to one-sixth of the original one, can be utilized in miniaturized GPS applications both in Cellphone as well as PDAGPS.The main results of this dissertation are listed as follows:The working principle and miniaturation solution of quadrifilar helix antenna are investigated. The working principle of GPS and its signal characteristic are introduced and the general requirements of GPS for receiving antenna are summarized as following: the antenna could provide uniform response over approximately the entire upper hemisphere and have the style of right-hand circular polarization, with the operation frequencies of 1575.42 MHz and 1227.6 MHz. With regards to precisely measuring receiver, the antenna should ideally provide uniform response in both amplitude and phase within the region of coverage. Based on this, special attention has been paid on the composition, working principle and performance characteristic of quadrifilar helix antenna, including quadrature phasing and balanced feeding. In addition, antennas for miniaturization and multi-frequency are also studied.A miniaturized dielectric-loaded quadrifilar helix antenna is designed, with the size ofΦ17.8mm×H10mm and high permittivity(εr = 38) dielectric infilled. With this configuration the structure employs balanced feed at the top and a choke sleeve balun in the lower portion that projects an almost balanced signal feed. It also achieves quadrature phasing using laser trimming at quadrifilar helix. We find the length of dielectrically-loaded Balun and quadrifilar helix by simulation suing HFSS simulation software. It is showed by research that dielectrically loading can provide more shrinking for quadrifilar helix antenna than bifilar helix antenna and the resonating frequency of the antenna decrease with the increase of width of the filar. The simulation results show that the antenna has a good cardioid-shaped pattern with a 3dB beamwidth more than 120 degrees, right hand circular polarization and the axial ratio is less than 3dB within main-beamwidth, and the discrimination between the right and left hand circular polarization reaches 30dB, showing a good performance.The miniaturized dielectric-loaded quadrifilar helix antenna that infilled by microwave ceramic dielectric is fabricated and it meets all the designing performance requirements. Five key steps in the antenna fabrication are fully explored, including the construction of ceramic core, deposition of Cu thin films, laser trimming helix, feed structure as well as frequency and phase trimming. The fabricated antenna sample is tested: the resonating frequency is 1576.62 MHz; 10dB band width is 5MHz,; the return loss is -17.5dB; the 3dB beamwidth is 120°; the antenna gain is -3dBi; the input impedance is 68.67-16.24jΩ. Comparing the measured results with the theoretical data, we found that the antenna meets all the design requirements and it is suitable for miniaturization GPS receiver in both the performance parameters and structure size.The fabrication is rather difficult due to the stereo-structure of antenna. In this study, we creatively employ the laser trimming technology in order to solve the problem of helix fabrication and performance trimming, which provides a new method in the industrialization of this antenna. In addition, according to references indexed, this kind of antenna has the advantage of small size and good receiving performance; hence it is one of the most promising components in the GPS. The next industrial development is undertaken in related enterprises. |
PDF Full Text Request