Research On Electromagnetic Metasurfaces For Controlling Radar Cross Section Of Antennas

With the rapid development of new systems of radar,the stealth characteristics of various military carriers such as aircraft and warships are gaining more and more attention.Low radar cross section of the carrier leads to low possibility of being detected by enemy`s radar,thereby improving the battlefield viability and penetration ability of one`s own goals.Antennas are essential for a variety of radio equipment,because it can effectively radiate electromagnetic waves in a specific direction of space or can effectively receive electromagnetic waves in a specific direction of space,it has a major contribution to the radar cross section of the entire equipment.In other words,due to the poor performance of the antenna RCS,the entire stealth property will be destroyed.Therefore,in the complex electromagnetic environment,in the case of the normal radiation characteristics of the antenna,the reserch on the technology of reducing the RCS of the antenna in a wide frequency band has become a hot topic in recent years.The author's main work in the thesis includes the following aspects:Firstly,a new type of polarization conversion surface is studied to reduce wideband RCS reduction of microstrip antenna.The Quadrate Fractal Structure and its mirror unit produce a phase difference of 180 degrees,the cross-polarized reflection waves on the operating were introduced to 90 degrees and-90 degrees phase shifts,respectively.Based on the checkerboard arrangement surface,the backscatterer energy is regulated to other directions,thus effectively reducing the monostatic RCS in the vicinity of the need.The results of numerical simulations show that the polarization conversion rate in the frequency band from 10.45 GHz to 32.15 GHz(relative bandwidth 101.9%)is greater than 80%.The proposed polarization conversion surface PCM is applied to the RCS reduction of the microstrip antenna,and the reduction in RCS of the antenna in the band from 8 GHz to 28 GHz is more than 5.68 d B.The polarization conversion mechanism of the polarization conversion surface is analyzed in detail,and this chapter furtherly explores the principle of monostatic RCS reduction,when the electromagnetic wave radiate vertically.Secondly,a low RCS waveguide slot antenna was designed with electromagnetic metasurface loading technology.The polarization conversion metasurface based on the Quadrate Fractal Structure is loaded on the waveguide slot antenna,and the orthogonally arranged polarization conversion metasurface array is advantageous in achieving wideband radar cross section reduction while ensuring the antenna radiation characteristics are not changed.The simulation results show that the impedance bandwidth,radiation pattern and the gain of the waveguide slot antenna are not affected after the polarization conversion metasurface is loaded.When the incident electromagnetic wave is normally incident with x-polarization and y-polarization,compared with the reference antenna,the RCS reduction of the designed antenna is more than 5d B at a wide frequency range from 7.5 GHz to 29 GHz(with a relative bandwidth of 117.8%),which is significantly covers the in-band and out-of-band of the resonant frequency of waveguide slot antennas.Thirdly,a design method of two-dimensional phase gradient metasurface is proposed,and the design conditions that need to be satisfied to effectively reduce RCS are analyzed.With broadband approaches studied,a phase-adjusted surface design based on the traditional Jerusalem cross center plus cross ring structure is proposed.Changing the size of the cross structure can change the abrupt phase of the reflected electromagnetic wave.Simulation and optimization results obtained through HFSS,get six different size cells,and the phase difference between adjacent cells remains basically unchanged at 13 GHz-15.6 GHz.Therefore,the phase gradient metasurface formed by this unit can realize the anomalous reflection of the electromagnetic wave,thereby reducing radar cross section of the vertical incident electromagnetic wave.The simulation results show that,compared with PEC surface,the RCS reduction of the phase gradient metasurface is more than 5d B in the range of 8.6 GHz to 17.5 GHz.