| The thesis is made on the basis of scientific projects for the wide beam circularly polarized array antenna used in differential global navigation satellite system(DGNSS).Firstly,the related reseach status as well as the backgroud and meaning of this topic are discussed.Secondly,the research contents of the thesis are introduced.Finally,the main research achievements of the thesis and the further research are indicated.The thesis consists of two main parts.A wide beam circularly polarized antenna element is proposed and fabricated in the first part.The simulated and measured results show that the designed antenna element meets the requirements of the array antenna.In the second part,a wide beam circularly polarized array antenna is presented by using the antenna element aforementioned.The simulation results meet the technical specifications and lay good technical foundation for the follow-up implementation of the array antenna.The two works are outlined as follows:1.Research on the wide beam circularly polarized antenna element According to the technical specifications from the array antenna and the theoretical knowledge of dipole and quadrifilar helix antenna,the design difficulties of the antenna element are analyzed and the implementation of the antenna element is determined.The antenna element composed of four slanted dipoles takes full advantage of the structure of quadrifilar helix antenna which has the characteristic of wide beam circular polarization.By using the printed balun that has parasitic microstrip,the slanted dipole can cover the operation band of DGNSS.Besides that,balanced feed can also be achieved.The simulated and measured results show that the right-hand circular polarization axial ratio of the presented antenna element is no more than 3dB in the beam range of 160°.2.Research on the wide beam circularly polarized array antenna According to the basic theory of linear array and linear array synthesis as well as technical specifications of the array antenna,the difficulties and implementation of the array antenna are discussed on the backgroud of specific engineering requirments.To track more GNSS satellites and suppress ground reflected multipath effect,the radiation pattern of the array antenna has a right-hand circularly polarized gain which is more than 0dB in the beam range of 160°,with a sharp cut-off characteristic around the horizon and 30 dB low sidelobes below the horizon.The design of the array antenna includes algorithm design and array antenna simulation.The algorithm design of the array antenna is based on the Fourier transform pair and the convolution method.By using these two methods,the pattern function and excitation function that are corresponding to the desired radiation pattern can be obtained.A 21-element array was chosen to design the array antenna with the element space about half of a wavelength.In the process of the array antenna simulation,a special ring for isolation and a ceramic rod for supporting the antenna elements are designed and used to weaken the coupling between the array elements and optimize the array antenna's characteristic of wide beam circular polarization.By adjusting the printed balun of the slanted dipole,the impedance matching of the array antenna can be optimized.The simulation results show that the proposed wide beam circularly polarized array antenna meets the technical requirements and lays the foundation for engineering implementation. |
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