Application Of Characteristic Mode Theory In Designing Circularly Polarized Antenna

Characteristic mode is a kind of analysis method which rises in recent years.,a new method is a combination of the eigenmode theory in solving electromagnetic problems using a moment method,it makes the method of moments have a more clear physical picture,through the analysis of different models of information,grasp its resonant characteristics and radiation characteristics.Provide an opportunities for antenna designers to better understand the mechanism of antenna.Also,it's helpful for designers to find the slot position in order to fine tune the resonant position.According to the traditional design of circular polarized antenna,the antenna designers rely too much on the engineering experience of the phenomenon,and gave full play to the advantages of characteristic mode theory.Based on the understanding of the basic working principle of the antenna,the design of the circularly polarized antenna is guided by the orthogonal characteristics and the intrinsic characteristics of the modes.The main contributions of this paper can be divided into the following aspects:In the first part,according to MOM and the integral equation,the characteristic mode theory is introduced.And the microstrip antenna is used as the research object.The analysis of the characteristics of microstrip antennas is presented to explore the influence that whether the existence of the H type slot in the microstrip antenna,and the influence of the different size of the floor on the resonant frequency.In the second part,the gene-encoding method in genetic algorithm is introduced to optimize the structure of circular polarization antenna,by characteristic mode theory.Especially,adding the parameters,like modal significance and characteristic angle,to design function named fitness.At the same time,we verified the the validity of the algorithm through the optimization examples.In the third part,under the guidance of the theory of characteristic mode,three circular polarized microstrip antennas are designed.First,through adding the AS microstrip,the stub loaded unequal current path in the destruction of the original antenna,the characteristic mode under the guidance of the theory of separation of the original weights degenerate in equal amplitude,angle difference of two kinds of features characteristic mode of 90 degrees,to obtain the desired circular polarized wave.Second,through adding the IF microsrip,increasing the current path of the rectangular groove embedded in the square patch in the intense disturbance when the size of the rectangular slot increases can cause surface characteristics of the antenna current,and can reduce the frequency characteristics of mold,destroy the original degenerate mode,generating the same amplitude,phase difference of 90 degree modal the realization of circular polarization.Third,through adding the LS microstrip,which circular polarization antenna is designed.