Study And Design Of Dual-Band Ground-Independent Antenna

With the rapid development of wireless communication application,the antenna serves as an important part of the wireless communication,whose performance directly affects the quality of the communication.And more technical requirements are put forward for antenna when applied in different scenarios.Miniaturization,broadband or multiband combination,environmental adaptability is the important direction of antenna.With the advent of the era of intelligent transportation,the communication service of transportation tools such as cars,trains will be more and more.The demands of the vehicle mounted antennas dramatically increase,but due to the obvious dependence of general antennas on ground,the antenna performance will change with the size of ground.Like the antenna on the car roof,the antenna should be designed in consideration of the size of the car and the location of the antenna.Likewise,the identical kind of antenna should be re-designed when installed in different trains or installed on the different positions of the train due to the equivalence of ground variation.The changes of ground will affect antenna performance,and if seriously,the antenna performance will be sharply deteriorated,which will not satisfy the requirements of the design.If the antenna designed has nothing to do with the ground or ground has little effects on the antenna performance as possible,the antenna performance is relatively stable,that is to say,the antenna has good environmental adaptability when ground size changes.It not only reduces the antenna installation complexity,but also spares human resources.Therefore,the independence study for antenna on ground has huge important practical significance on engineering applications.This paper detailed the studies on the Choke Column,Electromagnetic Band-gap(EBG)structure and Frequency Selective Surface(FSS)reducing the antenna effects on the antenna performance,and a kind of double-band vehicle mounted antenna with less correlation to ground has been realized in the way of combining choke column and EBG structure,which lays a foundation for the engineering application.The main contents of paper are as follows:First of all,choke column structure is put forward.Placing separate columns vertically in the printed monopole antenna ground and connecting them with ground,columns will be parts of the ground.As the changes of antenna ground,surface currentsare restricted in a smaller space by choking column,thus the surface wave diffraction reduces and the ground effects on the antenna performance is reduced.Then a mushroom type EBG structure is designed.Because EBG structure has band gap characteristics,the impedance will tend to infinity and thus electromagnetic waves resonating at the frequency can't spread through the EBG structure when at the resonance frequency of the EBG structure.The paper presents suppressing the surface wave propagation through the EBG structure,which reduced the antenna ground effects on the antenna performance.Finally a kind of single frequency WLAN antenna loading EBG structure with less dependence on ground is designed.And then the band-pass and band-stop characteristics of FSS structure are studied.The factors of influencing the FSS structure characteristics are discussed,and the characteristics of each unit of FSS structure are analyzed.By comparison,the square ring is finally selected as the basic units of FSS structure.A single-band and dual-band FSS structure units with band-stop characteristics are respectively designed and serve them as the grounds of designed single-band and dual-band WLAN antenna.Simulated and measured results show that the inhibition effect of FSS structure on the surface wave is better.Finally,a vehicle mounted antenna applied in railway GSM-R communication with no correlation for ground is designed in the combination of choke column structure and EBG structure according to the requirements of engineering,which saves the cost and reduces the complicated antenna installation process for railway communication system.This paper systematically studies the three structures reducing the antenna independence on the ground.By optimizing the structure design,the ground surface wave can be limited within a certain range of space,which reduces the edge surface wave diffraction effects on the antenna performance.Finally the antenna performance of reducing correlation for the ground is achieved and provides references for environmental adaptive antenna design.