Design Of Broadband Circularly Polarized Antennas Using Characteristic Mode Theory

In complex communication systems,circularly polarized antennas have the advantages of suppressing rain and fog interference,reducing multipath reflection and eliminating polarization mismatch,which can effectively improve the efficiency and stability of communication systems.Recently,the broadband circularly polarized antenna has become a research hotspot in the field of antennas,and the circularly polarized microstrip patch antenna has been widely studied because of its low profile,easy processing,and easy integration.However,the design of circularly polarized antenna in many cases is based on the designer’s experience,and this design method of circularly polarized antenna has some limitations.The characteristic mode theory can characterize the inherent resonance characteristics and radiation mechanism of the target structure from the working mechanism of the antenna,predict the potential performance of the target structure,and reduce the time of large-scale parameter optimization for antenna design,which has certain guiding significance for the design of circularly polarized antenna.Therefore,this thesis focuses on the impedance bandwidth and axial ratio bandwidth of circularly polarized antennas and designs two broadband circularly polarized antennas using characteristic mode theory as a guide.The main research content includes the following two aspects:I.A rectangular microstrip antenna is designed according to the empirical formula,and the potential performance of the rectangular structure is analyzed by the characteristic mode theory.A broadband circularly polarized monopole antenna was designed in combination with characteristic mode analysis of the rectangular structure,and the designed broadband circularly polarized antenna has 12.2%(2.3-2.6 GHz)and 53.7%(4.5-7.8 GHz)relative bandwidths and achieves 40.7%(4.9-7.4 GHz)relative axial ratio bandwidth.In the design process,two rectangular structures with different potential characteristics are combined,and the overall antenna structure has the conditions of potential circular polarization through reasonable modal modulation.Finally,a suitable feed position is found in the "Time Domain Solver",and the antenna structure is optimized to realize the broadband circularly polarized monopole antenna design.II.Based on the first part of circularly polarized monopole antenna design,the monopole antenna ground is further designed using characteristic mode theory,and the antenna performance is improved to a large extent by the slotted ground,achieving a relative impedance bandwidth of 118.5%(2.87-11.22 GHz)and a relative axial ratio bandwidth of69.1%(2.88-5.9 GHz).In the design process,the antenna front and back structures are analyzed separately using characteristic mode theory,and they can meet the conditions of potential circular polarization in the required band after reasonable mode modulation.Finally,according to the feed position analysis by the characteristic mode theory,the suitable feed position is found in the "Time Domain Solver",and the antenna structure is optimized to obtain the broadband circularly polarized performance.