Research On Radar Cross Section Reduction Of Antenna Array Based On Artificial Electromagnetic Metasurface

With the development of radar detection technology,the difficulty of penetration has increased greatly.In order to ensure the dominance of the war and improve the abilities of penetration and survival of the equipment,many countries have studied the radar cross section(RCS)reduction technology.As a main part of the communication system,the antenna array needs to radiate or receive electromagnetic waves effectively.This makes the RCS reduction of antenna array very difficult.The antenna array has become one of the main scattering sources for the stealth equipment.How to realize the wideband RCS reduction of the antenna array on the premise of ensuring the radiation characteristics has great research value.It is also a difficult problem in the design of RCS reduction of antenna array.Focusing on this problem,this dissertation proposes four new methods for RCS reduction of antenna array.The major contributions are summarized as the follows: 1.A design method of RCS reduction of antenna array based on phase gradient metasurface(PGM)is proposed.The mechanism of controlling the reflected wave by PGM is introduced.Unit cells which can maintain stable phase gradient in a wide bandwidth are designed after analyzing the reflection performances of different periodic structures.Then,a polarization independent two-dimensional PGM is designed by analyzing the influence of arrangement on scattering performance of metasurface.The designed PGM can achieve 10 d B RCS reduction from 7 GHz to 16.2 GHz.The PGM is loaded on the top of a microstrip slot antenna array.The antenna shares the metal structure with the PGM.The radiation performance of the antenna array is affected because of the changing of equivalent permittivity caused by the loading of PGM.Slots are cut on the substrate of PGM to reduce the impact on radiation performance caused by the loading of PGM.Due to the anomalous reflection and diffuse reflection of the PGM,the RCS of the antenna array is reduced from 7 GHz to 20 GHz.2.A low RCS antenna array with low profile based on polarization conversion metasurface(PCM)is proposed.The mechanism of RCS reduction based on PCM is introduced.In order to design a low RCS antenna array using the antenna units based on PCM,sequential rotating feeding network is needed so as to ensure the radiation performance of the antenna array.This brings the problem of selecting the polarization state of the antenna element.By analyzing the total gain of the antenna array with linearly and circularly polarized antenna element,it's found that the gain of the array with circularly polarized units is 3 dB higher than that with linearly polarized units.Thus,the antenna element with circular polarization radiation performance in the range of 6.1-6.7 GHz and polarization conversion performance in the range of 5.5-7.8 GHz is designed by exciting the PCM array using slot coupling structure.Combined with the sequentially rotated feeding network,the antenna array with low profile and circularly polarized radiation performance from 5.6 GHz to 7.3 GHz is designed based on this antenna element.The array has low RCS in the range of 5-9 GHz without any help of additional structures.3.Low RCS antenna arrays based on hybrid artificial magnetic conductors(AMCs)are proposed.The mechanism of RCS reduction based on AMCs is introduced.Two unit cells with 180°±30°reflected phase difference from 6.3GHz to 12.7 GHz are designed based on square patch and slot-cut-square patch structures.Then,two antenna units are designed by exciting the array structures composed by these two kinds of unit cells using slot coupling structure.These two antenna units have similar radiation performances in the range of 6.2-6.8 GHz.Two 2×2 antenna arrays composed by these two kinds of antenna units are designed.Good impedance matching is realized from 5.7 GHz to 7.5 GHz.The monostatic RCS is reduced from 6 GHz to 17 GHz which covers most of the operation bandwidth.The reduction value is higher than 5 d B in the range of 8-15 GHz.Antenna arrays with similar radiation performance and different scattering patterns are achieved by changing the arrangements of the units.4.A low RCS antenna array based on antenna units with 1-bit reconfigurable scattering characteristics is proposed.Based on the structure of traditional microstrip antenna,antenna unit whose radiation and scattering performances can be controlled independently is designed by cutting slots on the antenna ground.The pin-diodes are also applied in the design of antenna unit.The antenna unit can realize two different working states due to the difference of equivalent parameters of diodes under different working states.The working states of the antenna unit can be switched by controlling the voltage of diodes.The two working states have similar radiation performance at 5 GHz.For the scattering condition,the two states have 180° reflected phase difference if the polarization of incident wave is orthogonal to that of antenna.The two states both have absorbing properties while the polarization of incident wave is the same as that of antenna.The antenna array based on this antenna element can reconfigure the scattering pattern according to the requirement.The wideband RCS reduction or monostatic/bistatic RCS reduction at specific directions can be achieved with the help of optimization algorithm.