Research On Millimeter Wave Tightly Coupled Wide-band Wide-angle Scanning Technology

With the rapid development of communication technology,the transition of communication network from 2G to 4G only took decades.Today,the global process of5 G is already accelerating,and large-scale commercial 5G will be realized soon.One of the big trends in 5G is that the frequency band is constantly extending to the millimeter band.Due to the electromagnetic loss problem in the millimeter band and the signal quality problem in the transmission process,the application of 5G antenna will focus on the research of the array,especially the phased array,because the phased array can effectively alleviate the attenuation caused by the multipath effect of the signal for the virtue of its scanning characteristics.As the communication platform is more and more required to have the multi-function nature,the working frequency band of different functions is more discrete,in order to reduce the cost,the broadband antenna is also more and more needed with the development of communication.In summary,millimeter band phased array with broadband performance will become a focus in the development of 5G antenna.In this paper,with the wideband wide-angle scanning of the tightly-coupled wideband phased array as the target,the traditional tightly-coupled dipole array is studied for millimeter band.For the limitation of using the planar structure to realize the tightly-coupled array in the millimeter band,a tightly-coupled wide-angle scanning phased array antenna with a broadband of 25GHz~65GHz is designed.The main research contents and work summary are composed of the following three parts:The first chapter mainly describes the development process of millimeter wave antenna and phased array antenna and the research status of domestic and foreign researchers.The second chapter mainly describes the basic theoretical knowledge of antenna,which includes three aspects: the first is the basic index of the antenna unit;the second is two theories that are very important in the array antenna: the interference and superposition principle of electromagnetic wave and the product principle of direction diagram.The third is the infinite current sheet model and the tight coupling theory which is emphasized because it is the principle basis of the tight coupling structure.The third chapter first introduces TCDA Tightly Coupled Dipole Array(Tightly Coupled Dipole Array)which integrated balun,then put forward a kind of linearpolarization infinite Tightly Coupled Dipole phased Array antenna.Since the principle of broadband in the tightly coupling scheme can be summarized as utilizing the capacitive coupling between array elements,it is different from the traditional design process of phased array: design elements first and then array,meanwhile reduce the mutual coupling between units.In the tightly coupling scheme,the infinite array is simulated by periodic boundary conditions,and then the infinite array is processed by finite size.So the design of infinite array in tightly coupled array design is equivalent to the element design in traditional phased array design.Under the periodic boundary,the proposed infinite array overcomes the limitation of tightly coupled dipole scan array in millimeter band by improving the structure of dipole feed,and by adding inductance and capacitance in the feed structure,it satisfies the condition of tightly coupled broadband performance: the large ratio of characteristic impedance of its branch structure.In addition,the current distribution and electric field distribution of the proposed structure are researched,and the resonance current on the closed metal ring is processed by the metallized through hole to eliminate the matching degradation at some frequency points,the problem of peak of active standing wave is solved.In the end,the infinite array achieves the bandwidth of 25GHz~65GHz under the requirement of VSWR<3,and achieves the maximum scanning Angle of 70°for both E and H plane.In the forth chapter,a solution to the edge truncation effect of finite large array of tightly coupled structures is presented.The infinite array in the third chapter is made into 8×8 finite scale,and the problem of edge element mismatch in finite 8×8 array is greatly improved by using this scheme.The edge truncation effect of the finite coupled arrays is discussed firstly in this chapter by analyzing the unit boundary of the infinite coupled arrays.Then,combining with the unit structure in the third chapter,the edge truncation effect of finite large array is analyzed under three conditions: no scan,scan on plane E truncated and scan on plane H truncated.It is concluded that the edge truncation effect is the most significant in E-plane truncation in large Angle scanning.Finally,the edge truncation effect of E-plane truncation large-angle scan is improved.By making the feeding phase of the most marginal unit consistent with that of the adjacent unit when scanned at a large Angle instead of the normal feeding phase,the original situation that many units' VSWR not up to standard due to the boundary effect is improved.In the final 8 × 8 array scale,the bandwidth of 25GHz~65GHz was maintained,and the maximum scanning Angle of plane E and plane H was 70°.