| Ultra-wideband array antenna plays an important role in radar communication systems due to its excellent radiation performance,such as ultra-wide operating frequency band and wide-angle beam scanning.Whereas,it has also become an important scattering source on military platforms because of its high gain.Radar Cross Section(RCS)is a crucial parameter to use when assessing a target’s scattering properties.RCS reduction for military targets can reduce the detection probability of targets,thus improving the aggressivity and survivability of combat weapons,which is of great strategic significance in modern warfare.Nowadays,most of the research on antenna RCS reduction focuses on the single antenna,rather than large array antennas.Some low-scattering array antennas only work in narrow band,instead of broadband or ultra-wideband.Moreover,some studies fail to consider the co-polarized scattering wave.In order to break through the current technical bottleneck,this dissertation studies the RCS reduction technology of UWB array antenna comprehensively from three different parts: optimization for antenna element,arrangement for antenna array,and additional structure(metasurface)loading for antennas.The main contents of this dissertation are as follows:1.The theory and model of array’s antenna mode scattering analysis are established,and the structural mode scattering and the antenna mode scattering for array antenna are suppressed.The scattering field of an antenna can be divided into structural mode scattering and antenna mode scattering.At present,a lot of researches focus on the structural mode scattering,rarely on the antenna mode scattering.This dissertation aims at the copolarized scattering waves,and proposes a 98-element circular low-scattering Vivaldi phased array antenna which works on X-band(8～12 GHz).Firstly,based on the theory of antenna mode scattering,the structural mode scattering is reduced to the same level as the antenna mode scattering by loading radar-absorbing material and physically tilting.Based on this,the part of the antenna element that mainly contributes to the antenna mode scattering is extracted and analyzed in detail.Based on the substrate-integrated waveguide(SIW)technology,the antenna is loaded with metallized vias.At the same time,shape modification design and slotting treatment are carried out.Finally,the low-scattering Vivaldi array antenna is designed by synthesising the above technologies.For comparison,a reference array loaded with absorbing material but without antenna mode scattering reduction measures is designed.The two arrays have been fabricated and measured for verification.Experimental results show that they have similar radiation characteristics,both arrays can scan up to E-/H-plane ± 45°(VSWR < 3)operating in 8～12 GHz.However,the low-scattering array realizes an average value of 9.41 d B for monostatic RCS reduction in 8～12 GHz.2.The theory and model of array-level scattering cancellation are presented,and the RCS reduction method for array antennas is obtained.Due to that the traditional design of the array antenna from a single antenna element costs optimization and the process is complicated,it is necessary to analyze the scattering reduction of the array antenna from the array level.In this dissertation,a general design method is first proposed,two Vivaldi antenna elements with the same radiation performance but different reflection phases are designed.The two antenna elements exhibit similar radiation performance in 8～12 GHz and 180° reflection phase difference in 6～18 GHz,which satisfies the condition of array-level scattering cancellation.Then,the two different antenna elements are arranged as a chessboard,producing an ultrawideband low-scattering Vivaldi array antenna.Finally,two 16×16 chessboard-like Vivaldi phased array prototypes are fabricated and measured,one array is the low scattering array with two different antenna elements arranged on a chessboard,and another is the reference array consisting of uniform antenna elements.The experimental results show that the two arrays have similar radiative performance and can scan up to E-/H-plane ± 60°(VSWR < 3)in 8～12 GHz.However,the low-scattering array achieves a10 d B RCS reduction in the in-band and out-of-band broadband in 6～18 GHz,showing attractive low-scattering performance.3.Based on the principle that the reconfigurable surface can adjust the reflected and transmitted electromagnetic waves,a tightly coupled dipole array with low scattering and reconfigurable radiation patterns is designed.Metasurfaces have developed rapidly and made great contributions to the integrated control of antenna radiation and scattering.Nevertheless,most of them have only one single function and are unreconfigurable.Therefore,based on the principle that metasurfaces can regulate the reflected and transmitted electromagnetic waves,this dissertation proposes a dual-function metasurface.It is applied to the radiation beam control and low-scattering design of tightly coupled dipole array.The metasurface is composed of two units,one is responsible for regulating the reflected electromagnetic wave,and the PIN diode is loaded on it to regulate the reflected wave in two different frequency bands.Therefore,the low scattering characteristics on two different frequency bands are achieved.Another one is responsible for the modulation of transmitted electromagnetic waves,which can be adjusted by changing its coding arrangement,and then the radiation pattern can be reconstructed.Finally,the proposed metasurface is loaded on an 8×8 tightly coupled dipole array,performing two functions.The first function is to achieve RCS reduction in the dual-band of 8.25～12 GHz and 12～14 GHz with maximum values of 9.1 d B and 9.85 d B,respectively.The second function is to scan the radiation beam from 0° to 45° arbitrarily in the operating frequency band of 8～12GHz,and the radiation pattern can be reconfigurable. |
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