A Study Of Multi-line Helical Antennas

Nowadays, with the development of the global information revolution, the navigation and positioning system has become more widely used in civilian and military areas.Multi-line helical antenna, due to its wide band, wide lobe and good circular polarization characteristics, has become a hot topic in the field of navigation and positioning systems. In this thesis, through combining theory and practical application,the author studied a variety of multi-line circularly polarized wide beam helical antenna which are applied to navigation and positioning system. The main contents are as follows:Firstly, a right-hand circularly polarized cylindrical four-line helical antenna working at center frequency of 2.4GHz is simulated and fabricated, the diameter and height of the antenna is 0.22λ and 0.58λ respectively. With the simulation and analysis of the electromagnetic simulation software HFSS, the results show that S11 ? ?10d B when the frequency is between 2 ~ 2.8GHz, with the relative bandwidth of 33%, 3d B beam width of 180°, 3d B axial ratio beam width of 152°, achieving a hemispheric coverage characteristics; with a gain of 3.25 d B and the cross polarization better than 65 d B in the direction of maximum radiation. The test results are in good agreement with the simulation results.Secondly, a right-hand circularly polarized spiral printed four-line helical antenna with3 d B beam width of 188°is presented. The diameter and height of the antenna is 0.4λand 0.5λ respectively. The simulation results show that the return loss of the antenna is less than 10 d B when the frequency is between 2.28 ~ 2.6GHz, with the relative bandwidth of 13%, 3d B axial ratio beam width of 176°; with a gain of 3.1d B and the cross polarization better than 57 d B in the direction of maximum radiation. Also, we designed a new type quasi cylinder four helical antenna fed by SIW power divider. This antenna has solved the asymmetric problems in the cylindrical spiral antenna pattern owing to the SIW divider. The simulation results show that the return loss of the antenna is less than-10 d B when the frequency is between 2GHz ~ 2.8GHz, with the relative bandwidth of 33%, 3d B beam width of 196°, 3d B axial ratio beam width of 180°; with a gain of 3.45 d B and the cross polarization better than 78 d B in the direction of maximum radiation.Thirdly, with the combination of specific application occasion, several more specific circularly polarized antenna are designed and simulated, including the ultra-low-profile four-line helical antenna, the superfine four helical antenna with screw diameter of11 mm and the eight-line helical antenna. The three antennas all have wide band and wide beam characteristics, which can be applied in some of the more special occasions.