| Applying electromagnetic waves in the military field and improving radar detection technology have led to the development of stealth technology.Radar cross section(RCS)is a physical quantity that describes the stealth performance of a target.Thus reducing the RCS of a target implies that the target has a lower detectability.In recent years,metasurfaces have been widely used in the field of electromagnetic stealth to achieve RCS reduction due to their excellent electromagnetic wave manipulation properties.In this paper,based on the previous research,reflective metasurfaces are studied to achieve RCS reduction,which includes phase modulated metasurfaces and polarization conversion metasurfaces.The main contents are as follows.1.Electromagnetic stealth is achieved based on phase modulation metasurfaces.In this paper,two phase modulation metasurfaces with low RCS characteristics are designed.The first one is a ternary metasurface with cascaded phase differences.First,the ideal reactance curve with a 180° phase difference at the operating frequency point is used as the phase elimination condition.Secondly,the unit structure and phase elimination condition are linked together using parallel resonant circuits to realize the eliminated phase difference between the units,and this design idea improves the efficiency of unit design.Finally,three units with cascaded phase differences are formed into a ternary metasurface,which achieves RCS reduction in the range of 6.5-16.7GHz.The second one is a metasurface with shared perforating holes.The shared perforating holes of adjacent units are realized on the covering layer by using the periodic property of the metasurface unit.The shared perforating hole widens the operating bandwidth of the unit to 8.5-35.3GHz and introduces a new degree of freedom for the optimization of the unit.In the metasurface design,a random metasurface arrangement is first obtained using an annealing evolutionary algorithm.Then,the random arrangement is optimized a second time using convolution operation to achieve a uniform and dispersive effect of the reflected energy beam on the metasurface.In turn,ultra-broadband RCS reduction(relative bandwidth 126%)is achieved in the 8.2-36.4GHz.2.Electromagnetic stealth is achieved using a polarization conversion metasurface,and the metasurface is applied to the RCS reduction of a magnetoelectric dipole antenna.A "two-blade paddle" type metasurface unit with high polarization conversion is designed and flipped to the left and right to obtain the corresponding mirror unit.The two units are loaded onto the magnetoelectric dipole antenna and the unit positions are optimized using convolution operations.The measured result shows that the metasurface antenna operates with 26% bandwidth(12-15.6GHz).Compared with the reference antenna,the RCS of the metasurface antenna is reduced by more than 10 d B in 9.9-16 GHz band.Thus,it is verified that the metasurface antenna achieves in-band and out-of-band RCS reduction while ensuring the original radiation performance. |
