Technology And Application Of Radiation And Scattering For Ultra-wideband Phased Antenna Array

Phased antenna array occupies an important position in modern radar and communication system,since it has fast beam scanning and precise beam pointing.On the other hand,future radar communication system extremely demands an advanced integrated platform with multiple functions including communication,radar stealth,electronic warfare,and so on.Therefore,it leads to an urgent demand to design a future phased antenna array(PAA)with wideband impedance matching,low profile,and low scattering properties simultaneously.The phased antenna array with enhanced coupling(PAA-EC)employs the mutual coupling between adjacent antenna elements to achieve wideband impedance matching.In addition,recent researches have demonstrated that the PAA-EC has advantages of low profile and low scattering with respect to the conventional PAA.Thus,this dissertation further proposes the wideband impedance controlling and scattering reduction method for the PAA-EC.On the other hand,for the study of the scattering reduction,the simulated validations of large-scale PAAs take a large amount of computing time.Thus,a fast analysis method of scattering from the large-scale PAAs is proposed in this dissertation.The main contents of this dissertation are summarized as follows:1.Studies on the impedance matching technology of the wideband PAA-EC using equivalent circuit model(ECM)Since the PAA-EC includes strong electromagnetic coupling and complicated integrated feeding structure,time-consuming simulation inevitably becomes an obstacle of its design procedure.Based on the conventional ECM of the PAA-EC,this dissertation developes an accurate full equivalent circuit model for the bowtie dipoles and integrated balun.By employing the novel ECM,we could efficiently control the impedance characteristics of a dual-polarized wideband and wide-scanning PAA-EC.Then,the PAA-EC achieves a good impedance matching among the operation band of UHF-X.The simulated results show that it achieves 12.5:1(0.8?10 GHz)bandwidth for active VSWR<2.5 when scanning up to±45°.Moreover,a 10×10 prototype of the PAA-EC is fabricated and measured for validating the simulation results.The measured results demonstrate that the proposed dual-polarized wideband and wide-scanning PAA-EC achieves excellent wideband impedance matching.O n the other hand,to further solve the engineering problem of the dual-polarized PAA-EC requiring difficult fabrication,we propose a novel dual-polarized PAA-EC with dual-diamond dipoles and twin-slot balun.In addition,an accurate ECM for the irre gular dipoles and twin-slot balun is proposed.By employing it to adjust the impedance characteristic of the antenna element of the PAA-EC,the PAA-EC achieves an excellent impedance matching among the UHF-X band.The simulated results show that the proposed PAA-EC exhibits 11.3:1(0.8?9 GHz)bandwidth for active VSWR<3 within the scanning range of±60°.Moreover,a 10×10 prototype of the PAA-EC is fabricated to validate its simulated performance.2.Studies on the low-profile and low scattering PAA-EC using destructive interferenceVery few researches focus on the scattering characteristics of the PAA-EC.With respect to the conventional low scattering PAA-EC with additional metamaterial,this dissertation proposes a low-profile and low scattering chessboard-like PAA-EC without additional loading structures based on the destructive interference.The proposed chessboard-like PAA-EC consists of two different types of low-profile planar antenna elements that have similar radiation pe rformance in the X-band.In addition,the two types of antenna elements have a 180°±37°reflection phase difference over the X-band,which guarantees the cancelation of scattering fields for low scattering purpose.On the other hand,an 8×8 reference PAA-EC and a low scattering PAA-EC are developed and fabricated to validate the radiation performance and scattering characteristics.Both of the full-wave simulation results and measured results are presented.It shows that the proposed low-profile planar PAA-EC(0.127?_high)operates in the 8?12 GHz band with±45°scanning range.It also achieves at least 9-d B radar cross section(RCS)reduction in the 8?15.2 GHz band as compared with the reference PAA-EC.3.Studies on the fast analysis method of the scattering from the large-scale PAAs using characteristic modes theoryThe conventional method of moments(MoM)needs a large amount of computing time and memory in solving the scattering of the large-scale PAA.Thus,this dissertation proposes an accurate and fast scattering analysis method by employing the characteristic modes theory.Specifically,a generalized eigenvalue equation is formulated from a MoM impedance matrix of the EFIE-PMCHWT(electric field integral equation and Poggio,Miller,C hang,Harrington,Wu and Tsai)formulation to obtain modal currents for an antenna element with MDCS.These modal currents are then used as entire domain basis functions in the MoM for expanding equivalent currents over a large antenna array with MDCS.Only a small number of the modal currents are required to approximate the induced current over the antenna array with sufficient accuracy.Thus,the number of the unknowns and the corresponding CPU(central processing unit)time in the MoM are significantly reduced in the proposed method.Furthermore,as the periodicity and intrinsic relationship of the matrix elements are considered when using the modal currents as entire domain basis functions,the computational efficiency of the proposed method is further improved.Numerical results of typical antenna arrays with MDCS are presented to illustrate the efficiency and accuracy of the proposed method.