Design Of Broadband Circularly Polarized Antenna Based On Characteristic Mode Theor

The rapid development of mobile communication technology has put forward higher requirements for modern electromagnetic communication system,and the design of circular polarization antenna with broadband performance is one of the effective ways to meet the needs of contemporary massive data communication.Characteristic mode theory can express the inherent resonance and radiation characteristics of the antenna in a clear physical concept,which is independent of external excitation.It helps to guide the design and optimization of the antenna,simplifies the traditional antenna design process,and has become a research hotspot in the antenna field.In this thesis,the broadband circularly polarized antenna will be analyzed and designed with the help of characteristic mode theory.The specific research work can be summarized as follows:1.An ultra-wideband circularly polarized printed monopole is designed and optimized based on classical characteristic mode theory.Starting with the mode analysis results of elliptical patch and elliptical ring patch,the asymmetric patch of elliptical arc is selected as the radiation structure,and then the characteristic mode analysis of patch and monopole antenna is carried out respectively,and a monopole antenna with broadband circular polarization performance is designed.Then,based on the idea of fractal antenna,by introducing parasitic structure,a new characteristic mode which can form circular polarization radiation is introduced to optimize the impedance matching and circular polarization performance of the antenna.Finally,the working bandwidth of the antenna is 72.7%and the circular polarization bandwidth is 57.4%.The feasibility of designing and optimizing wideband circularly polarized monopole antenna guided by characteristic mode theory is verified.2.Two metasurface circularly polarized antennas are designed based on the characteristic mode theory of planar layered structure.By comparing the characteristic mode analysis results of radiation surface with different patch numbers,it verifies that the broadband performance can be achieved by using patches with the size is far smaller than the wavelength.Then based on the mode analysis of the metasurface radiation structure of 4×4 circular element patch,the appropriate characteristic modes are selected as the circular polarization target mode according to the characteristic current distribution and far-field directivity.Then,according to the phase conditions,the phase difference is constructed in two ways by designing the feed part and modifying the shape of super surface patch,and two metasurface circular polarization antennas are designed.The working bandwidth of the former is 35.1%,and the shaft ratio bandwidth is 19.2%;The relative bandwidth of the latter antenna is 32.8%,and the relative bandwidth of circular polarization is 13.1%.It is verified that the characteristic mode theory can guide the design of the metasurface circularly polarized antenna.