Research On Circularly Polarized Crossed-Dipole Antennas For Satellite Communications And Navigations

As one of key technologies in wireless communication systems,circular polarization has the advantages of suppressing multipath interference,alleviating polarization mismatch,and resisting Faraday rotation effect in the ionosphere.When applied to the antenna design,it can make up for the defects caused by linear polarized?LP?antenna.With the rapid development of satellite communication and navigation systems,the circularly polarized?CP?antennas with the characteristics of broadband,low profile,wide beamwidth,and high gain have become pop-ular.Due to the fact that the crossed-dipole antennas can easily achieve broadband circularly polarized radiation characteristics,they cause the interesting of researchers in the scientific community.This work was supported in part by the National Natural Science Foundation of China?61372008?,and in part by the Science and Technology Planning Projects of Guangdong Prov-ince?2014A010103014,2015B010101006?.Considering the performance requirements of the current satellite communication and navigation systems for circularly polarized antennas,the basic characteristics of the conventional crossed-dipole antenna structure and its shortcomings in the applications,three circularly polarized crossed-dipole antennas are investigated in the thesis.The specific research contents are summarized as follows:?1?A novel circularly polarized wide-beam crossed-dipole antenna.A circularly po-larized antenna for main and minor wavebands in global position system?GPS?is proposed.Four parasitic vertical right-angle plates are introduced around the cross dipole.Two pairs of crossed-dipole arms consisit of rectangular patches and vertical copper pillars to realize 90°bending of the dipole arms,widening the beamwidth.The proposed antenna can achieve 3-d B axial ratio beamwidth of more than 120°within 44.8%of the circularly polarized bandwidth.Moreover,the half-power beamwidth can exceed 125°.?2?An ultra-wideband circularly polarized crossed-dipole antenna.A circularly po-larized crossed-dipole antenna which can cover the whole L band of satellite communication and GNSS band is presented.Its structure is relatively simple and compact,then the working principle is analyzed.With the aid of wind vane shaped dipoles,the proposed antenna achieves multiple impedance passbands,broadening the impedance bandwidth.The introduction of four vertical parasitic metal plates generates additional axial passband and greatly improves the cir-cularly polarized bandwidth.Therefore,the 3-d B axial bandwidth of the antenna is increased from 21%to 74%,and the profile of the proposed antenna is further lowered to 0.20?₀.Besides,the gain in the workingband is very stable with the variation of less than 3 d B.?3?A low-profile circularly polarized crossed-dipole antenna based on AMC.A circu-larly polarized crossed-dipole antenna which can cover part of the C band of satellite commu-nication is presented.To address the issue of the relatively high profile and low gain of the preceding two antennas,the third antanna equipped with the structure of artificial magnetic conductor?AMC?is designed.Low profile can lower the wind resistance in harsh environment and high gain increases signal coverage in a certain direction.By loading the AMC structure,the profile of the antenna is reduced to 0.13?₀,the surface wave is effectively suppressed and the backward radiation of the antenna is eliminated.By loading the rectangular parasitic ele-ment,the additional axial ratio?AR?passband can be generated to broaden the 3-d B axial ratio bandwidth of the antenna.Therefore,the proposed antenna can achieve 39%of the circularly polarized bandwidth in the profile of 0.13?₀.The propoed antenna was fabricated and tested.The measured results of the antenna are very consistent with the simulated ones.The average gain of the antenna in the whole working band is 8.3 d Bi.In this thesis,three circularly polarized cross dipole antennas are designed,and the works of circularly polarized antennas are integrated.They have the advantages of wide beamwidth,broadband,low profile,and high gain.Consequently,the three proposed high-performance an-tennas have great competitiveness in satellite communication and navigation systems.