Research On Directional Wideband Circularly Polarized Antennas

The research works are made based on scientific projects.In this thesis,the directional wideband circularly polarized(CP)antennas are studied.This thesis consists of three parts.In the first part,a directional wideband CP electromagnetic dipole antenna is developed,which solves the problem of narrow bandwidth of CP electromagnetic dipole antenna.In the second part,a CP crossed dipole antenna with broadband characteristics and stable gain is developed.In the third part,a CP crossed dipole antenna with wide bandwidth and wide axial ratio beamwidth is developed.The main contents of the research work can be summarized as follows:1.Wideband CP Electromagnetic Dipole Antenna According to the design requirements of wideband CP electromagnetic dipole antenna,the coupled feed method is used to widen the impedance bandwidth in the design process,and the method of widening the axial ratio bandwidth of CP electromagnetic dipole antenna is discussed.Based on the designed antenna model,the prototype is developed and tested.The test results show that the designed antenna can achieve an impedance bandwidth of 67.6%(1.82~3.68 GHz)and an axial ratio bandwidth of 62.5%(1.91~3.65 GHz),which meets the design requirements of wideband CP electromagnetic dipole antenna.2.Wideband CP Crossed Dipole Antenna A wideband CP crossed dipole antenna is developed.In the design,the bandwidth of the antenna is improved by using broadband feed network and introducing parasitic structures.The experimental results show that the impedance bandwidth and the axial ratio bandwidth of the developed antenna can reach 41%(1.75~2.65 GHz)and 36.6%(1.83~2.65 GHz)respectively,and the variety of antenna gain is not more than 1d B in the whole axial ratio bandwidth.The antenna has a good stability.All of the results meet the requirment,which verifies the feasibility of the design.3.Wideband CP Crossed Dipole Antenna with Wide Axial Ratio Beamwidth According to the design requirements,a wideband CP crossed dipole antenna with wide axial ratio beamwidth is developed.A broadband phase-shifting feed network is used to widen the bandwidth of the antenna,and the axial ratio beamwidth of the antenna is widened by introducing a cylindrical metal cavity.The prototype is tested,and the test results show that the antenna can achieve an impedance bandwidth of 67.6%(1.82~3.68 GHz)and an axial ratio bandwidth of 62.5%(1.91~3.65 GHz),over which the antenna gain varies from 4 d Bic to 6 d Bic.The minimum axial ratio beamwidth of the antenna reaches 100°,while the maximum axial ratio beamwidth of the antenna is as high as 245°.The antenna has good radiation characteristics,and its electrical performances satisfy the target requirements.