Fund Project:Project supported by the National Natural Science Foundation of China (Grant Nos. 61671464, 61701523, 61801508), the Natural Science Foundational of Shannxi Province, China (Grant Nos. 2017JM6025, 2019JQ-103), and the Postdoctoral Innovative Talents Support Program of China (Grant No. BX20180375)
Received Date:24 June 2020
Accepted Date:26 July 2020
Available Online:08 December 2020
Published Online:20 December 2020
Abstract:An aperiodic metasurface antenna array with low radar cross section (RCS) is designed. The upper patches of the two antenna elements have the same shape and are placed at an orthogonal position, which can effectively reduce the workload of simulating the reflection characteristics of the patch. As antenna elements, they have identical operational band and polarization mode, and as metasurfaces, they can form an effective phase difference of 180° ± 37°. The RCS of the array is reduced mainly by phase cancellation under the x polarization and by absorption under the y polarization. According to the coding metamaterial theory, the two elements can be coded aperiodically by using the programming software. Regarding element A and element B as “0” and “1”, respectively, the coding matrix can be solved by a genetic algorithm. Element A and element B are arranged according to positions “0” and “1” to obtain a proposed array. The scattering field of proposed array is diffusive, and the peak RCS is effectively reduced. In order to highlight the characteristics of the proposed array, the chessboard-type array is designed for comparison. The simulation results show that the radiation performance of proposed array is good. Comparing with the metal board of the same size, the 6 dB reduction bandwidth of the monostatic RCS is 4.8-7.4 GHz (relative bandwidth is 42.6%) under the x polarization and 4.6-7.8 GHz (relative bandwidth is 51.6%) under the y polarization. Comparing with the chessboard type array, the scattering energy distribution of the designed antenna array is very uniform and the peak RCS in space reduces obviously. When a 4.8 GHz electromagnetic wave is incident with different incident angles and polarization modes, the scattering field is diffusive. Compared with other similar arrays, the proposed array has advantages of simple design process and even scattering field. The experimental results are in good agreement with the simulation results. This work makes full use of the scattering characteristics of the antenna element itself to solve the problem that the array antenna possesses both good radiation characteristics and low scattering characteristics at the same time, and improves the design process of the antenna patch. This design method has certain universality and reference significance for designing the low RCS antenna array. Keywords:low radar cross section/ patch antenna array/ diffusion
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3.低RCS天线阵设计与仿真为实现组阵后阵列具有低RCS特性, 选取单元A与单元B各8个进行组阵. 同时为保证天线阵具有漫散射特性, 利用遗传算法算出在6 GHz时阵列RCS峰值最小时的排布方式. 把单元A和单元B视作“0”和“1”, 作为变量代入适应度函数中, 设置种群规模为500、保留最佳个体数量为10、交叉概率为0.75、变异概率为0.2, 运行程序算出使适应度函数最小时所对应的编码方式, 把单元A和单元B按该编码方式排列, 得到最终设计出的天线阵列, 如图7(a)所示, 其中心4个单元命名为E1, E2, E3, E4. 为更好说明所设计天线阵的工作特性, 使用传统棋盘式天线阵作为对比, 如图7(b)所示. 两阵列大小均为120 mm × 120 mm, 相邻贴片单元中心间距为30 mm. 图 7 天线阵列结构示意图 (a) 设计天线阵; (b) 棋盘式天线阵 Figure7. Geometry of (a) proposed array and (b) chessboard type array.
对天线阵中16个天线单元进行等幅同相馈电, 得到天线阵的辐射特性如图8所示. 两天线阵辐射特性相似, 设计天线阵在4.6—5.4 GHz仿真实际增益在15.5 dBi以上; 天线阵中心单元受耦合影响较小, –10 dB阻抗带宽较其单独工作时基本不变; 设计天线阵辐射方向图良好, 在最大辐射方向处交叉极化较低. 图 8 两天线阵列辐射特性 (a) 实际增益曲线; (b) 设计天线阵中心单元的|S11|曲线; (c) 设计天线阵在5 GHz时的辐射方向图; (d) 棋盘式天线阵在5 GHz时的辐射方向图 Figure8. Radiation characteristics of two arrays: (a) Realized gain; (b) |S11| of elements of proposed array; radiation pattern of (c) proposed array and (d) chessboard type array at 5 GHz.