| Phased array antennas are widely desirable in the wireless communication systems of modern military and commerce with the characteristic of very high speed and sensitivity for electronic scanning,as well as their remarkable agility for beamforming and nulling.Compared with mechanically scanned counterpart,phased arrays take the advantages of powerful reliability,strong anti-interference ability,multi-target tracking capacity,function reconfigurability and multi-tasking operation.With the rapid development of information science and radio technology,the array antennas of modern radar,navigation and satellite communication systems are being developed toward wide-range coverage,high responding speed,multi-function and multi-polarized radiation.To address the abovementioned challenges and meet the demands of low cost,low profile and high level of integration,planar wide-angle scanning arrays are investigated.Because of mutual coupling between array elements,the active impedance of planar wide-angle scanning array varies significantly versus scanning angle,which usually results in the deterioration of the active standing wave ratio,the degradation in transmitted power while steering the main beam to particular angles,the fading of active gain,the sharp fluctuation of realized gain as the beam switches and even the scanning blind spots.To deal with these challenges,the theory and key techniques of wide-angle impedance matching(WAIM)on planar phased arrays are thoroughly researched in this dissertation.From the perspective of suppressing or compensating mutual coupling effect between elements,WAIM is implemented for one-dimensional(1-D)and two-dimensional(2-D)wide-angle scanning arrays.The main content of this dissertation is arranged into the following three parts:Part ?: The ultra-wide-angle scanning and WAIM methods of 1-D planar arrays are researched,including the wideband designs.The innovations and contributions of this part can be summarized as the following two aspects.1.With the theoretical analysis,the ultra-wide-angle scanning potential of the 1-D array is verified,and the impact of mutual coupling on the performance of electrical scanning is clarified.Thereby,an effective ultra-wide-angle scanning solution is derived in which the broadening of half-power beamwidth(HPBW)for array element is organically combined with the suppression of mutual coupling.In the actual design,an ultrawide HPBW is attained for the isolated element based on the joint effect of the spatial radiation from the microstrip patch and the surface-wave diffraction,and the inherent field distribution at apertures of each element is properly regulated so that the mutual impedance between two arbitrary elements can be reduced substantially.In the practical prototype,an artificial impedance surface is implemented and integrated into the periodic patch array to support the surface-wave transmission,and the narrow slots backed on the special waveguides are proposed as the excitation sources for surface waves.With the cooperative analysis of near-field,far-field and surface-wave couplings,the surface waves are identified as the dominant effect.The mutual impedance due to the surface-wave modes is suppressed by regulating the inherent field distribution of the excited element,and therefore WAIM is achieved.2.The cooperative design of mutual coupling compensation and ultra-wide-angle scanning is realized for the large-scale 1-D array over a wide band.To design the array element,a multi-resonant model is proposed by integrating the substrate integrated waveguide with the inverted microstrip patch,and multiple parallel slots are etched to expand the operation bandwidth.Then,a compact,periodic,low-profile and ultra-wide-angle scanning array is implemented with the proposed element antenna.With the concept of mutual coupling compensation,the impacts of far-field and surface-wave couplings are effectively compensated by utilizing multiple symmetrical slots backed on the substrate integrated waveguide.By loading the metasurface layer,the variation of active impedance due to the near-field coupling is further compensated,and therefore superior wideband WAIM is realized.The proposed design responses to the problem that the mutual coupling suppression is hard to be compatible with wideband ultra-wide-angle scanning capacity with low-profile design.Part ?: The wide-angle scanning and WAIM solutions of 2-D large-scale planar arrays are researched,including the wideband designs.The innovations and contributions of this part can be summarized as the following two aspects.1.With the cooperative analysis of array factors and the mutual coupling effect,the scanning bottleneck of the large-scale 2-D array and the impact of mutual coupling on the electrical beam scanning are clarified.It is expected that wide-angle scanning with high merits of WAIM will be implemented while the isolated element pattern is shaped into the cosine form and mutual coupling is suppressed simultaneously.To verify the hypothesis,one novel WAIM solution based on the compensation of isolated element patterns and the cancellation of common-mode couplings is proposed.Within the actual element,to shape the isolated element patterns into the cosine tendency,one pair of symmetric slots are etched as radiating apertures on two interconnected substrate integrated cavities,and the reactive feeding network are packaged in the cavities to excite the balanced symmetric radiation of the two slots.Actually,by optimizing the spacing between such two slots,nearly cosine-type patterns are formed for the isolated element in E-and D-planes.With the rigorous analysis of the differential-mode and common-mode couplings,the cancellation of common-mode couplings is enhanced by loading the dielectric superstrate and resonant wave-trap structures,which caters for the WAIM.To attain the wide-scan capacity with perfect WAIM,both cosine-type isolated element patterns and fully suppressed mutual coupling are pursued.2.Both cosine-type isolated element patterns and fully suppressed mutual coupling are pursued over a wide band to explore the wideband wide-scan capacity with perfect WAIM.For the actual design,the dispersion metasurface and reactive feeding network are utilized to realize wideband mutual coupling suppression,which is applied to a 2-D periodic triangular-lattice array.The proposed array element is implemented on a low-profile substrate integrated cavity.Multiple dumbbell-shaped slots are etched on the cavity as the radiating apertures,and dispersion metsurfaces are loaded atop the cavity.A reactive network is embedded in the substrate integrated cavity to excite the equal-amplitude and in-phase radiations of the slots.Owing to the dispersion characteristic of the metasurface,the isolated element not only embodies the wideband feature,but also radiates the nearly cosine-type patterns in plane E-and plane D-planes.With the even-mode and odd-mode analysis,both even-mode and odd-mode coupling currents are induced on the reactive network.Based on the analysis of equivalent circuit model for the coupled element,it is proved that even-mode current is vital to active mismatch.Since the dispersion metasurface is loaded atop the radiation slots,the inverse-phase cancellation of even-mode couplings can be precisely enhanced,and therefore the WAIM is achieved.Part ?: The wide-angle scanning and WAIM methods of 2-D wideband dual-polarized array antennas are researched.The innovations and contributions of this part can be summarized into the following two aspects.1.With the Floquet mode analysis,a WAIM technique with the regulation of surface-wave modes is proposed.A cylindrical substrate integrated waveguide is utilized within the proposed array element to package the two orthogonally arranged U-shaped feeding networks,and a cross-type slot is implemented as the excitation aperture on the waveguide cavity.A cylindrical hollow cavity,double-layer circular patches and arc-shaped parasitic strips are stacked above the slot.Since the array element possesses a cylindrical profile,it is suitable to be applied in a 2-D dual-polarized array with periodic triangular lattice.The array prototype has the possibility of supporting TM mode surface waves,and the surface-wave dispersion characteristics are demonstrated by Floquet analysis and full-wave simulation technology.The WAIM is implemented by removing the surface-wave modes,therefore,an optimized array lattice is selected and the design of introducing periodic parasitic hollow cavities into the array is proposed.2.For wideband dual-polarized phased array antenna,conjugated active impedance matching method based on the metasurface WAIM layer is proposed.With the pre-designed dual-polarized array,one double-layer metasurface WAIM layer is mounted over the element on the premise of maintaining overall profile height.With the equivalent circuit model,the advantages of expanding the operation bandwidth with the WAIM layer is clarified.Actually,according to the Floquet analysis,the WAIM layer introduces equivalent shunt susceptance that varies with beam scanning angle,which can effectively compensate the variation of Floquet impedance at the interface between the array and the free space with the scanning angle,resulting in superior WAIM. |
PDF Full Text Request