Research And Design Of Novel Ultra-wideband Tightly Coupled Array Antennas

With the rapid development of modern wireless communication technology,antennas,as an important part,have been put forward higher requirements for its performance and parameters.Because of its special value in research and application,array antennas with wideband and high gain have become more widely used in radar and communication system.The traditional wideband array antenna first designs an independent broadband array unit,and then avoids the coupling between the units as much as possible,but in general,the coupling effect between units will have an adverse effect on the performance of the array.In contrast,the tightly-coupled array antenna takes advantage of the coupling effect between the elements and can also realize the miniaturization of the array while broadening the frequency band.In this paper,based on the tightly coupled array theory,several wideband and high gain tightly coupled antenna arrays are designed and studied by using a dipole antenna with broadband and low cross polarization as the array unit.Firstly,the research background and significance of the tightly coupled array antenna are briefly introduced,and the research status is briefly described.In addition,some related theories of tightly coupled arrays are analyzed in detail.Secondly,based on the ordinary planar tightly coupled dipole array,two eight-element one-dimensional tightly coupled dipole linear arrays are designed and studied by improving the structure of the antenna.The first antenna,starting with the dipole antenna unit,adds a vertical structure at the end of the dipole arm.The antenna bandwidth is broadened by the capacitive reactance produced by the structure and the mutual coupling effect generated by the array element after the array.The impedance bandwidth of the antenna is 4.76 GHz to 13GHz(92.79%),the average realized gain is above 9dB,and the maximum is 10.7dB.The other antenna is to load the parasitic patch on the basis of the ordinary planar tightly coupled dipole array.The antenna bandwidth is broadened by the coupling effect between the parasitic patch and the dipole antenna.The impedance bandwidth of the antenna is 4.56 GHz to 13.3GHz(97.87%),the average realized gain is above 9d B and the maximum is 11.05 dB.The above two antennas have good linear polarization characteristics,and their crosspolarization isolation degree is higher than 50 dB.Finally,a simple analysis of the interdigital tightly coupled structure is carried out,and a eight-element one-dimensional tapered interdigitated dipole tightly coupled linear array is designed in combination with the tightly coupled array theory.Based on the common interdigitated structure,this antenna improves the general “finger” to a gradual “finger” at the end of the dipole,which not only greatly improves the impedance characteristics of the array at high frequencies,but also reduces the cross-polarized level of the antenna to some extent.The impedance bandwidth of the antenna is 5.3GHz~15GHz(95.57%),the average realized gain is above 10 dB,the highest is 12.95 dB,and the cross-polarization isolation is higher than 26 dB.Compared with the first antenna,the antenna reduces the array from 113.6mm to 85.4mm while maintaining broadband,high gain and low cross polarization.The antenna length decreases by 24.8%.A linear gradual balun is designed for the antenna,which realizes the balance-unbalance transformation and impedance matching between the antenna and the coaxial feeder.