Research On Low Frequency Tightly-coupled Array Antenna Technology

Ultra-wideband antenna plays an important role in military wireless communication system,especially in the common UHF and VHF military target detection and electronic reconnaissance,and the bandwidth determines the detection ability.The tightly coupled array antenna utilizes the strong coupling between the elements to expand the bandwidth and has the characteristics of low profile and wide band,which effectively solves the problems of large size profile and difficult installation of low frequency antenna.In this dissertation,the development history of wideband antenna is firstly introduced,and then the key technologies of tightly coupled ultra-wideband array antenna are summarized.This paper focuses on the low frequency tightly coupled array antenna technology.Firstly,the equivalent circuit model of tightly coupled array element is established based on periodic array analysis method.Combined with circuit simulation and full-wave simulation,the mutual coupling effect of antenna and the effect of reflected ground and wide Angle matching layer are analyzed,and the UWB mechanism of tightly coupled array antenna is expounded.Then,we explain the common mode resonance problem of array antenna.Taking tightly coupled antenna array simulation as an example,the causes and types of common mode resonance are analyzed in detail,and common common mode solutions are discussed to provide theoretical basis and basis for subsequent antenna design.In this dissertation,two tightly coupled array antennas operating in 110-520MHz are designed and developed.The first antenna combines the advantages of low frequency and excited by the co-designed integrated transformer Balun.Each array element is protected from the effect of the common mode resonance by setting the shorting posts between the dipole and the ground,and a printed Frequency Selected Surface is used in place of the bulky dielectric superstrates.The truncation effect is analyzed by simulation of finite × infinite period array,and the the problem is solved by setting the virtual cell.The final array achieves the performance of 5:1 bandwidth with VSWR<2.5 when scanning±50° in E plane and±40° in H plane.The second TCDA is excited by the integrated Marchand Balun and second order Wilkinson power divider,and each array element is divided into two dipoles to avoid common mode resonance.A printed Frequency Selected Surface is used for wide-angle scanning in palace of the medium superstrate.The truncation effect is analyzed by simulation of finite × infinite period array,and the the problem is solved by setting the virtual cell.The final array achieves the performance of 5:1 bandwidth with VSWR<2.5 when scanning±50°in E plane and VSWR<3.0 when scanning ±40° in H plane.Finally,two antenna array prototypes are made based on the simulation models,and the Active VSWR and coupling coefficient of the antenna elements are tested in the field.The performance of the two antennas is comprehensively analyzed combined with the simulation results.