| With the rapid development of electronic communication technology,the performance of detection equipment is improved more quickly,and the importance of equipment stealth is becoming increasingly prominent.At the same time,antenna is an element with strong scattering ability,and effective reduction of radar cross section of antenna has become one of the important research directions.In recent years,electromagnetic metasurface can obtain the desired electromagnetic characteristics by artificial flexible arrangement,which has attracted extensive attention.The polarization radar waves can be converted to other forms by the polarization conversion metasurface,and radar cross section can be well reduced when metasurface is applied correctly.Therefore,the low radar cross section antenna based on polarization conversion metasurface is studied in this thesis.The contributions and innovations of the research work are as follows:Firstly,a low radar cross section slot array antenna is designed.The polarization conversion metasurface element of the proposed structure has a polarization conversion bandwidth of 8.55-23.79 GHz(94.24%),and an X-band four-element slot array antenna fed by a one-quarter T-type power divider is designed.The number of metasurface elements and their mirror elements are arranged in a chessboard pattern as the chessboard metasurface and placed above the slot antenna.When irradiated,the reflected waves generated by the two types of elements have the same amplitude and the phase difference is 180 degrees,and the reflection cancellation achieves the reduction of radar scattering cross section.Compared with results presented in literatures,the radar cross section of the proposed antenna is reduced by more than 5d B in the range of 8.2-23.8 GHz(97.5%),with an average reduction of 12.5 d B in the band and a maximum reduction of 26.8 d B at 21 GHz.Secondly,an ultra-wideband circularly polarized microstrip antenna with low radar cross section is designed.The hybrid feed network is composed of Wilkinson power divider and 90-degree phase shifter.The design can provide two signals with equal amplitude and 90-degree phase difference for patch antenna,and ensure the radiation performance of antenna in circular polarization.The unit cell of novel wideband polarization conversion metasurface with frequency band 9.46-20.01 GHz(71.6%)is designed.The chessboard metasurface is arranged on the same plane of the patch,which has the advantage of low profile.The results show that the antenna has the ultra-wideband characteristics of 6.78-8.85 GHz(26.48%)and the axial bandwidth of 7.31-8.88 GHz(22.03%),and the radar cross section is reduced by more than 5 d B in the range of 8.5-21.5 GHz(86.67%),and the maximum reduction value at 19.8 GHz is 34.3 d B.Thirdly,in this thesis,a method is proposed to solve the problem of antenna gain loss after adding a metasurface.By observing the electric field phase distribution of the antenna and the metasurface in the same section,some unit cells of metasurface which are opposite to the antenna electric field phase are removed,and the problem of the antenna with low radar cross section decreasing compared with the original antenna was solved effectively,and the reduction of the radar cross section was not significantly affected.The method is used to analyze the gain decrease of the ultrawideband circularly polarized microstrip antenna with the addition of polarized metasurface.some unit cells of metasurface which are opposite to the antenna phase are found by using the electric field phase distribution,and the gain of the antenna is further increased by more than 1 d B after removing these unit cells.By analyzing and solving the coupling problem between the antenna and the polarization conversion metasurface,the antenna has no obvious performance attenuation.It not only improves the radiation characteristics of the antenna,but also has a good effect of reducing the radar cross section. |
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