Collaborative Studies On Radiation And Scattering Characteristics Of Tightly Coupled Wideband Phased Arrays

Phased antenna arrays have the advantages of fast beam scanning and flexible beamforming and have been widely used in modern radar and communication systems.Furture multifunction electronic systems will consolidate communication,radar,electronic warfare,global positioning system,etc.,sub-systems into a single aperture,thus putting forward the urgent demands of phased arrays with wide bandwidth,wide scanning volume,low profile and low scattering simultaneously.The mutual coupling effects between adjacent elements are treated as favorable factors in tightly coupled wideband phased arrays,which have attractive merits in wideband,wide-scanning and low-profile natures.The idea of phased arrays design based on tight coupling has broken through the limitation of the traditional theoretical framework and promisingly open up a new way for the realization of wideband and wide-scanning phased arrays with low profile and low scattering characteristics.From the perspective of solving the aforementioned requirements of phased arrays,this dissertation is mainly focused on the collaborative studies on radiation and scattering characteristics of tightly coupled wideband phased arrays and several effective scattering control methods for such type of phased arrays.The main contents of this dissertation are summarized as follows:1.Studies on balance between radiation and scattering characteristics of tightly coupled wideband arraysThe studies on tightly coupled wideband arrays are generally focused on their radiation characteristics,and the scattering characteristics are rarely taken into account.In this dissertation,studies on balance between radiation and scattering characteristics of tightly coupled wideband arrays is carried out.Specifically,an implementation method of an ultra-wideband and wide-scanning tightly coupled dipole arrays with ultrawideband low backscattering characteristics simultaneously is proposed.In our design,the dielectric superstrate placed over the antenna aperture is optimized rapidly and efficiently based on a two-port network equivalent analytical model.Meanwhile,the feed structure of the array is well optimized.Consequently,a balance between the ultrawideband and wide-scanning radiation characteristics and the ultra-wideband low backscattering characteristics of the proposed array are accomplished.To quantitatively investigate the low scattering performances of the proposed array,a tapered slot array is selected as a reference array which features comparable radiation performances.Prototypes for a 6 × 6 proposed array and a 4 × 8 reference array with the same aperture size have been fabricated and measured for verification.Experimental results show that the proposed array achieves 4:1(4~16 GHz)bandwidth for active VSWR < 3.5 when scanning up to ±60°.Additionally,the proposed array can effectively achieve at least 5 dB monostatic radar cross section(RCS)reduction for an ultra-wide bandwidth ranging from 4 to 18 GHz at normal incidence with respect to the reference one.Moreover,the monostatic RCS of proposed array is also significantly reduced within a certain angular region in different planes.2.Studies on low-profile and low-scattering tightly coupled wideband arrays using artificial magnetic conductor ground planesThe dielectric superstrates are always required to achieve wideband and widescanning performances of conventional tightly coupled wideband arrays.Unfortunately,this would increase the profiles of antenna arrays and make the array bulky when applied to lower frequency bands such as UHF band.To solve this issue,a low-profile wideband tightly coupled dipole array excluding the use of any superstrate layers is proposed,where the power divider in feed network is placed horizontally on the ground plane.Rectangular parasitic strips are loaded on each side of the radiation aperture to guarantee the wideband and wide-scanning capacities.The overall thickness of the proposed array is only 0.27? corresponding to the highest operating frequency,which is much lower than other studies.Then,the proposed array is backed by an artificial magnetic conductor(AMC)ground plane which is covered with polarization conversion metamaterial(PCM)unit cells in a chessboard configuration.In this way,out-of-band backscattering suppression is accomplished effectively because of phase cancellation principle with the in-band radiation performances well preserved.For validation,an 8 × 8 array prototype is fabricated and measured.Experimental results demonstrate that the array exhibits 4:1(0.5~2 GHz)bandwidth for active VSWR < 3.1 within the scanning range of ±60° in Eplane and ±45° in H-plane.Moreover,by using the AMC ground plane,the proposed array achieves an ultra-wide out-of-band monostatic RCS reduction from 6.0 to 18.0 GHz under near-normal incidence.Further,we present an improved scheme of balun structure that can fully meet the demands of typical multilayer PCB manufacturing tolerances when the desired operating band is higher.In this way,an integrated wideband tightly coupled dipole array is designed,showing 3:1(6~18 GHz)bandwidth for active VSWR < 3.0 at ±60° scans.3.Studies on in-band scattering control of tightly coupled wideband arrays based on phase optimization techniquesIn order to overcome the limitations of the in-band scattering control methods which focused on the design of the array elements only,a more flexible systematic methodology based on phase optimization techniques is proposed to control the in-band scattering of tightly coupled wideband arrays.The key idea is that by only optimizing the phase excitation at the feed port of each element,the scattering control within the designated angular region can be accomplished,while the radiation performances are well preserved in the operating band.In order to realize a systematic and fast optimization process of the phase excitations,fast and effective synthesis methods for scattering and radiation properties of the array with additional phase contributions are introduced,where all the mutual coupling effects are taken into account.Then a collaborative optimization approach is adopted to optimize the scattering and radiaton properties of the array,thus achieving a balance between radiation and scattering characteristics of the array.A specific scattering reduction optimization example of a linear array with 16 elements operating in 8~12 GHz for scanning up to ±60° is used to validate the proposed approach.