Research On Polarization-Related Metasurfaces And Their Applications In Antenna Radar Cross-Section Reduction

With the development of radar detection technology,the electromagnetic environment in modern warfare is becoming more complicated,and the threat to combat platforms is growing.Radar stealth technology is an effective means to shorten the enemy radar warning time and improve the penetration and survivability of combat platforms.Recently,with the development of stealth shaping and radar absorbing material,the platform itself has achieved a lower scattering level.The antenna has become the main scattering contribution source,and its scattering characteristics determine the overall stealth level of combat platforms.However,the antenna as a transceiver of electromagnetic waves has special stealth design methods different from the general scatterer.It should be noted that antenna scattering reduction design must to guarantee the normal radiation properties.Therefore,it is of great theoretical value and military significance to carry out research on the reduction of antenna radar cross-section.With the support of the National Natural Science Foundation of China(NSFC)program,this thesis conducts research on the theory and design of polarization-related metasurfaces and their application in the comprehensive optimization study of the radiation and scattering characteristics of antennas and antenna arrays.The main contents of this thesis are summarized in the following five areas: 1.Research on the polarization conversion metasurface.The phase constraint range of the design of the reflective metasurface to realize linear polarization rotation and linear-tocircular polarization conversion is summarized.Based on this principle,a polarization conversion surface with frequency-selective characteristics is proposed,which can realize linear polarization to right / left circular polarization conversion from 6.87 GHz to 16.83 GHz,linear polarization to left / right circular polarization conversion from 19.72 GHz to 23.64 GHz,and linear polarization rotation from 17.38 GHz to 18.6 GHz.And then,a liquid metal alloy based controllable polarization conversion metasurface is proposed.Through reasonable design of the microfluidic channel structure,a polarization-related metasurface with three operating states switched by the filling layout of the liquid metal alloy is obtained.The three switchable working states contains: total reflection characteristics like metal plates,linear polarization rotation from 6.4 GHz to 20.2 GHz,and linear polarization to circular polarization conversion from 7.6 GHz to 15.5 GHz.2.Research on the low RCS circularly polarized antenna with gain enhancement.An ultrawideband polarization-related metasurface achieving the linear polarization rotation with the PCR higher than 0.9 from 7.55 GHz to 20.74 GHz(relative bandwidth 93.2%)is proposed.And a chessboard layout surface with low-scattering characteristics resulting from the polarization cancellation between polarization rotation metasurface and its mirror structure is presented.The low-scattering surface is then served as the loading structure for a circularly polarized patch antenna resonating at 8.2 GHz to enlarge the effective radiation aperture while maintaining low RCS feature.Compared with a reference antenna without the loading metasurface,the radiation gain is increased by 2.5d B.In summary,gain enhancement and the in-band and out-band RCS reduction of a circularly polarized antenna are realized simultaneously.3.Research on the low RCS circularly polarized antenna array with axial ratio bandwidth broadening.A polarization rotation metasurface ensuring PCR higher than 0.9 from 7.6 GHz to 10.46 GHz is served as the loading portion for a circularly polarized patch antenna.The bandwidth of the circular polarization axial ratio can be broadened by properly adjusting the relative location between the two structure.Compared with the unloaded case,the circular polarization axis ratio bandwidth is widened from 4.25 % to 11.18 %.Combined with the enlarge of the effective radiation aperture after loading and the polarization cancellation between the polarization rotation metasurface and its mirror structure,the proposed antenna achieves both gain enhancement and in-band and out-of-band RCS reduction.Sequential rotation of the designed low RCS circularly polarized antenna elements to form an antenna array further increases the circular polarization axial ratio bandwidth to 15.2%.In summary,this design method broadens the axial ratio bandwidth while realizing the RCS reduction of a circularly polarized antenna array.4.Research on the low RCS circularly polarized antenna array with high aperture efficiency.Low RCS antennas based on metasurfaces usually suffer from a low aperture efficiency(below 51%).To address this problem,a radiation-scattering integrated unit is designed to realize circular polarization radiation in X-band during radiation,and as a polarizationrelated metasurface unit reflecting electromagnetic wave cancels with the reflected wave from its mirror structure to realize monostatic RCS reduction during scattering.Then,the integrated unit using the sequential rotation feed technology forms a sixteen-element antenna array that can achieve circularly polarized radiation characteristics in the X-band with the circular polarization axial ratio bandwidth of 21.26 %.The realized gain at 10 GHz is 16.3 d Bic and the calculated aperture efficiency is as high as 74.63 %.Moreover,the antenna array has the inborn low RCS characteristics form 7 GHz to 15 GHz covering the working frequency band.In summary,a circularly polarized antenna array with high aperture efficiency and in-band plus out-of-band RCS reduction is realized.5.Research on the low RCS antenna array with reconfigurable scattering patterns.A liquid metal alloy based metasurface with controllable reflection phase is proposed.Under ypolarized normal incidence,the metasurface unit has either a 0° or 180° reflection phase response from 8 GHz to 32 GHz controlled by the injection of liquid metal alloy.Then the metasurface is used as a coating of a slot antenna to manipulate the phase of the scattered electric field without affecting the radiation performance.A 2 × 2 antenna array is then formed,and the layout of the liquid metal alloy in the cladding structure is controlled by the pressure-controlled drive of the syringe to make the antenna array has four operating states with the same radiation characteristics and different bistatic scattering patterns.Three of the four operating states can achieve monostatic RCS reduction in the range of 8 GHz to 32 GHz.In summary,a low RCS antenna array with reconfigurable scattering patterns based on the pressure-driven liquid metal alloy is realized.