The Study Of Wideband Beam Scanning Antenna Based On Tightly Coupled Theory

As one of the mostly used beam-scanning antenna,phased array is widely used in communication,detection,and other fields due to its flexible beam scanning ability.With the expansion of spectrum and the higher requirements of system,the antennas are highly demanded with wider bandwidth,higher gain,and larger scanning angle.Tightly coupled array achieves ultra-wideband impedance matching characteristics by introducing the tight coupling between elements,thus becomes the research hotspots in the recent years.In addition,as a kind of novel transmission line,gap waveguide has a low transmission loss at millimeter-wave(mm-Wave)band.Thus,a high-efficiency wideband phased array antenna can be obtained at mm-Wave band by combining the gap waveguide with the concept of tightly coupled antenna.Moreover,a broadband high-gain beam-scanning antenna with a limited scanning angle can also be realized by the combination of tightly coupled array and reflector antenna.The main contents of this paper are as follows:Firstly,the theory of antenna array,the theory of tightly coupled array,the applications of long slot antenna to tight coupled theory,and the basic theory of ridge waveguide and gap waveguide are introduced.Then,a long slot antenna element loaded with ridge structures is proposed.The scanning performance of the element is improved by adding ridges.After that,a 1×16 linear array is built up based on the proposed element,which can realize ±60°beam-scanning angle with a bandwidth of 40% from 20 GHz to 30 GHz.Considering the feasibility of the feeding structure,the microstrip line is selected in the design of 1-to-16 equal power dividers with equal/unequal phase.Besides,the transition structure from the microstrip line to the ridge gap waveguide is also designed.Finally,the whole array is designed,fabricated,and measured,and the simulated and measured results are in a good agreement.Secondly,the principle,method and design process of using phased array as a feed of the reflector antenna is studied to achieve high-gain beam-scanning performance.Broadband performance is achieved by using a dual-polarized tightly coupled Vivaldi array,which exhibits a good impedance matching characteristic within the frequency range from 4GHz to 8GHz when array elements are fed uniformly.Then,the focal field of the reflector are analyzed,and the size of the array and the excitation coefficients of the elements are obtained.The final simulated results of the system are obtained by taking the radiation patterns of the elements into the simulation of the reflector.It is seen that the scanning beam direction is consistent with the theoretical results.The antenna can scan at 0,1,2,3 and 4 times of HPBW direction at three frequency points of 4 GHz,6 GHz and 8 GHz.