| Radar is the "clairvoyance" in modern warfare,which is emerged and accompanied by electronic warfare.Presently,the technology of long-range radar detection is developing and updating rapidly."Stealth" is the opposite of the radar;stealth technology is to let the opponent "invisible" technology,which is the anti-radar technology accompanying with the rapid development of radar detection technology.Radar cross section(RCS)is one of the most critical technology specifications to evaluate stealth performance.For fighters,bombers,and other aircraft,the stealth performance depends largely on the RCS.The reduction of the scattering characteristics of the aircraft platform itself is relatively easy to achieve,so the equipped various antennas and their arrays with energy scattering and radiation have become the most easily "seen" part,which is the largest contribution of the aircraft's total RCS.Radiation is the most basic characteristic of an antenna,and it is contradictory to scattering.In the design of a low RCS antenna array,how to ensure that the radiation performance is not affected is a key technical problem.Therefore,this thesis focuses on polarization conversion metasurfaces(PCM)which can reduce antenna RCS,and designs two kinds of PCM,which are respectively applied to RCS reduction of linear-polarization and circular-polarization slot antenna arrays.The main works completed include:(1)A low RCS linear-polarization slot antenna array based on dual-patch PCM is designed.The dual-patch PCM structure can reflect the linear-polarization perpendicular incident wave with the polarization direction rotation of 90 degrees and is used to construct a metasurface with low RCS characteristics.The proposed dual-patch PCM unit is composed of two square defected patches printed on the top side of the dielectric substrate with a metal ground plane on the bottom side,and each patch is connected to the ground plane by three metal vias.The constructed low RCS PCM achieves a monostatic RCS reduction of more than 5dB in the frequency band from 6.5 to 13.5 GHz.By combining the dual-patch PCM with the 2×2 linear-polarization slot antenna array,the RCS reduction of more than 5 dB is realized in the frequency band from 6.6.to 13.6 GHz,and the maximum RCS reduction reaches 40 dB.Since the 5-dB polarization conversion bandwidth of the dual-patch PCM unit is basically the same as that of the 5-dB RCS reduction bandwidth of the slot antenna array,the proposed design method is simple and easy to implement.The RCS reduction of PCM and its applied antenna array in the same frequency band can be controlled only by adjusting the technology specifications of the polarization conversion unit.The measurement results are in good agreement with the simulation results,and the correctness of the design method is verified.(2)A circular-polarization slot antenna array with low RCS based on split-ellipse dual-ring PCM is designed.The metal stripes of the open-ellipse dual-ring PCM unit are arranged alternately on the top and bottom sides of the dielectric substrate and connected by metal vias.The metal via along the z-axis and the metal strip on the xoy plane constitute a 2.5-dimensional PCM structure,which realizes the PCM RCS reduction of more than 5 dB in the frequency band from 4.9 to 15.3 GHz.The reflection and transmission characteristics of the proposed open-ellipse dual-ring PCM structure are combined to improve the performances of the circular-polarization slot antenna array.On the one hand,the RCS of the circular-polarization slot antenna array in the frequency band from 4.8 to 14.9 GHz is reduced by more than 5 dB,and the maximum RCS is reduced with 30.1 dB by using the advantage of the reflection characteristics of the open-ellipse dual-ring PCM structure.On the other hand,by using the transmission characteristics of the open-ellipse dual-ring.PCM structure and combining the Fabry-Perot resonator theory,the gain of the slot antenna array is improved in the frequency band from 9.0 to 11.2 GHz,and the gain is increased by 3.4 dB at 10.8 GHz. |
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