Research On Broadband And Wide Beam Circularly Polarized Antenna

With the development of wireless satellite communication,the satellite navigation system has become more and more important in modern society.Due to the fit character of the circularly polarization antenna in the satellite communication system,the researches on those antennas are of much importance.Antenna with wide beam axial ratio radiation pattern could receive more signals in different directions,thus it could improve the accuracy of the positioning.In the satellite application,there are different working bands distribution.The broadband antenna could cover those bands simultaneously,thus reduce the antenna numbers required and achieve the equipment miniaturizaion.Planar circularly polarzied antenna is commonly used in the circularly polarized antenna designing.The structure of the thesis is organized as follows:Chapter ? The reserach background and significance are reviewed.Besides some antnnas broad axial ratio band property itself,to broaden the axial ratio band,the main approach would be improve the feeding structure and bringing in new modes to generate new axial ratio minimum point.The wide beam could be achieved by loading parasite unit.At the last of chapter,the structure arrangement of dissertation is provided.Chapter ? Briefly elaborated the theory circularly polarized antenna,which include the basic parameters of antenna,the theory of the microstrip antenna,and theory of the microstrip circularly polarized antenna.It afford the theory basis of the designing in broadband and wide beam circularly polarized antennas.In Chapter ? proposed a microstrip circularly polarized antenna.Through rotating the monopole antenna relative angle to the center axis of the semicircle background,the asymmetry of the structure could generate circularly polarization.In order to broaden the bandwidth,changing the structure by loading the square patch at the end of the monopole.In order to improve the match of impedance,using the stepped line to replace the microstrip.The axial ratio bandwidth of antenna is 54.8%,and the impedance match is good within the band.In Chapter IV proposed a slot circularly polarized antenna.Through sequentially rotated techniques to generate circularly polarization.In order to broaden the bandwidth,changing the structure by adding stub slot.The axial ratio bandwidth of antenna is 54.8%,and the impedance match is good within the band,which cover the GPSL1 band center frequency point(1.575GHz).In order to improve the match of impedance,loading a round plate above the antenna.At the end of this chapter,also propose two structures to correct the radiation pattern and improve the low elevation angle polarization gain.In Chapter V propose an antenna combine an ominidirectional and broadside circularly polarized antenna.The combined antenna could achieve 170 degree spanning 3dB axial ratio angle in the center frequency of GPSL1 band(1.575GHz),and in ± 64 degree the antenna could maintain ominidirectional characteristics.