Research On The Influence Of Common-mode Current To Antenna Testing And Its Overcoming Method

With the advent of the fifth generation of mobile communications,people are getting stricter with the speed and quality of information transmission.The antenna,as the carrier of information transmission,is naturally required to be high-gain,broadband,miniaturization and so on.When people are dedicated to improve the performance of the antenna,they also need to spare some effort to the research of antenna testing at the same time.Antenna testing can not only detect the actual performance of the antenna,but also reflect the differences between theoretical design and the actual performance.The most important part of antenna testing is the matching technique of the antenna to be tested and the feeding cable.If there is a mismatch between them,serious error will be made of the testing result.The most typical example is that the electrically small size antenna of mobile phone is easily affected by the common-mode current on the feeding cable,resulting in a change in the radiation performance of the antenna.Based on this background,this paper designs a new type of balun for parasitic current reduction applied to the use of antenna measurement.The main content of this paper is as follows:(1)Briefly introduces the influence of common-mode current induced by unbalanced feed on the radiation performance of the standing wave,gain,efficiency and radiation pattern of the antenna,and verifies that the common-mode current is the second source of radiation other than the antenna by simulation and actual test.(2)Brings forward the theory of balanced feed by analyzing the influence of common mode current on the radiation performance of the antenna.Elaborates the related theory and the importance of balanced feed to the antenna.Then introduces the research done by the predecessors in solving the problem in unbalanced feeding,which provides ideas for the design of the new common-mode current reduction balun.(3)Proposes the design scheme of the new common-mode current reduction balun based on the previous research.Analyzes the principle of the common-mode current reduction balun in detail to form a complete design flow.Optimizes parameters of the common-mode current reduction balun with the help of HFSS software.Confirms the influence of the common-mode current reduction balun on the radiated performance of the standing wave,gain and radiation pattern of the antenna and the suppression of the common mode current Verifies the universality of such a common-mode current reduction balun by the simulation and actual testing of different types of antennas.