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Novel design of microstrip antenna array with low scattering performance

Lan Jun-Xiang Cao Xiang-Yu Gao Jun Han Jiang-Feng Liu Tao Cong Li-Li Wang Si-Ming

Novel design of microstrip antenna array with low scattering performance

Lan Jun-Xiang, Cao Xiang-Yu, Gao Jun, Han Jiang-Feng, Liu Tao, Cong Li-Li, Wang Si-Ming
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  • In this paper, the idea of electromagnetic surface (EMS) is introduced into the design of microstrip antenna array. The antenna element proposed in this paper is treated as an EMS element, whose reflection characteristics are taken into consideration in the process of antenna array design. Firstly, a rectangular patch antenna element is designed. Then, by cutting arc-shaped structure into a rectangular patch, another element is created to generate 180° ± 30° effective phase difference compared with original antenna element. As a consequence, 180° ± 30° effective phase difference is obtained from 5.5 GHz to 6.9 GHz for the y-polarized incidence. Meanwhile, for the x-polarized incidence, each of the two elements possesses high absorptivity over the operating frequency as a result of matching load. Besides, the two elements work in the same resonant mode and the same resonant frequency band when treated as radiators. In order to further explain the consistency in radiation and difference in reflection between the two structures, current distribution at 5.8 GHz is investigated in terms of radiation and reflection. Then, the two elements are arranged into a chessboard array to achieve the low scattering performance based on phase cancellation principle under the y-polarized incidence. Based on the absorption principle, the matching load is added to improve the scattering performance of the composite antenna array with the x-polarized incidence. Simultaneously, the proposed antenna array maintains good radiation characteristics due to the consistency between the radiation performances of the two elements. The corresponding antenna array is fabricated and tested. Simulated and measured results prove that the proposed antenna array also achieves good radiation performance. And a 6 dB radar cross section reduction is obtained from 5.6 to 6.2 GHz under the x polarization and from 5.5 to 7.0 GHz under the y polarization for the normal incident wave, implying 10.1% and 24% in relative bandwidth, respectively. In-band reflection suppression in the specular direction is demonstrated for an incident angle of 30° under both polarizations. The measured results are in good agreement with the simulated ones. Additionally, the approach proposed in this paper offers an effective way to deal with the confliction between radiation and scattering performance, and can also be applied to other kinds of antenna arrays.
    [1]

    李文强, 曹祥玉, 高军, 赵一, 杨欢欢, 刘涛 2015 物理学报 64 094102

    Li W Q, Cao X Y, Gao J, Zhao Y, Yang H H, Liu T 2015 Acta Phys. Sin. 64 094102

    [2]

    Jiang W, Zhang Y, Deng Z B, Hong T 2013 J. Electromagn. Waves 27 1077

    [3]

    姜文, 龚书喜, 洪涛, 王兴 2010 电子学报 38 2162

    Jiang W, Gong S X, Hong T, Wang X 2010 Acta Electronica Sinica 38 2162

    [4]

    Genovesi S, Costa F, Monorchio A 2014 IEEE Trans. Antennas Propag. 62 163

    [5]

    Landy N I, Sajuyigbe S, Mock J J, Smith D R, Padilla W J 2008 Phys. Rev. Lett. 100 207402

    [6]

    Lan J X, Cao X Y, Gao J, Cong L L, Wang S M, Yang H H 2018 Radioengineering 27 746

    [7]

    Zhang C, Cheng Q, Yang J, Zhao J, Cui T J 2017 Appl. Phys. Lett. 110 143511

    [8]

    Paquay M, Iriarte J C, Ederra I, Gonzalo R, Maagt P 2007 IEEE Trans. Antennas Propag. 55 3630

    [9]

    Zheng Y J, Gao J, Xu L M, Cao X Y, Liu T 2017 IEEE Antennas Wirel. Propag. Lett. 16 1651

    [10]

    Wang H B, Cheng Y J 2016 IEEE Trans. Antennas Propag. 64 914

    [11]

    Xu G Y, Hum S V, Eleftheriades G V 2018 IEEE Trans. Antennas Propag. 66 780

    [12]

    Jia Y T, Liu Y, Zhang W B, Wang J, Wang Y Z, Gong S X, Liao G S 2018 Opt. Mater. 8 597

    [13]

    Zheng Q, Guo C J, Ding J 2018 IEEE Antennas Wirel. Propag. Lett. 17 1459

    [14]

    杨欢欢, 曹祥玉, 高军, 刘涛, 马嘉俊, 姚旭, 李文强 2013 物理学报 62 064103

    Yang H H, Cao X Y, Gao J, Liu T, Ma J J, Yao X, Li W Q 2013 Acta Phys. Sin. 62 064103

    [15]

    Zheng Y J, Cao X Y, Gao J, Yuan Z D, Yang H H 2015 IEEE Antennas Wirel. Propag. Lett. 14 1582

    [16]

    Liu Y, Li K, Jia Y T, Hao Y W, Gong S X, Guo Y J 2016 IEEE Trans. Antennas Propag. 64 326

    [17]

    Joozdani M Z, Amirhosseini M K, Abdolali A 2016 Electron. Lett. 52 767

    [18]

    Su J X, Kong C Y, Li Z R, Yin H C, Yang Y Q 2017 Electron. Lett. 53 520

    [19]

    Kang X L, Su J X, Zhang H, Yang Y Q 2017 Electron. Lett. 53 1088

    [20]

    Zhang C, Gao J, Cao X Y, Xu L M, Hang J F 2018 IEEE Antennas Wirel. Propag. Lett. 17 869

    [21]

    孙慧峰, 邓云凯, 雷宏, 焦军军, 石力 2012 中国科学院研究生院学报 29 282

    Sun H F, Deng Y K, Lei H, Jiao J J, Shi L 2012 J. Graduate Sch. Chin. Acad. Sci. 29 282

    [22]

    李响 2017 硕士学位论文 (南京: 南京信息工程大学)

    Li X 2017 M. S. Thesis (Nanjing: Nanjing University of Information Science & Technology) (in Chinese)

  • 图 1  单元三维结构示意图 (a) 单元1; (b) 单元2

    Figure 1.  Geometry of (a) element 1 and (b) element 2.

    图 2  匹配负载对EMS1反射特性的影响 (a) 反射幅度; (b) 反射相位

    Figure 2.  Reflection characteristics with and without matching load: (a) Reflection magnitude; (b) reflection phase.

    图 3  不同参数对EMS1反射特性的影响 (a) l1对反射幅度的影响; (b) l1对反射相位的影响; (c) s1对反射幅度的影响; (d) s1对反射相位的影响; (e) w1对反射幅度的影响; (f) w1对反射相位的影响

    Figure 3.  Effects of various parameters on reflection performance: Effects of l1 on (a) reflection magnitude and (b) phase; effects of s1 on (c) reflection magnitude and (d) phase; effects of w1 on (e) reflection magnitude and (f) phase.

    图 4  弧形缺口对天线|S11|及y极化下反射相位的影响

    Figure 4.  Influences of arc-shaped structure on reflection coefficient |S11| and reflection phase.

    图 5  天线单元辐射特性 (a) |S11|; (b) 方向图

    Figure 5.  Radiation properties of two elements: (a) Reflection coefficients |S11|; (b) two-dimensional radiation patterns at 5.8 GHz.

    图 6  EMS反射特性 (a) 反射幅度; (b) 反射相位

    Figure 6.  Reflection characteristics of two elements: (a) Reflection magnitude; (b) reflection phase.

    图 7  表面电场与电流分布 (a) E1在5.8 GHz的表面电场分布; (b) E2在5.8 GHz的表面电场分布; (c) EMS1在5.24 GHz的表面电流分布; (d) EMS2在6.86 GHz的表面电流分布

    Figure 7.  Surface E-field distributions at 5.8 GHz of (a) E1 and (b) E2; surface current distributions (c) at 5.24 GHz of EMS1 and (d) at 6.86 GHz of EMS2.

    图 8  设计天线阵的模型示意图

    Figure 8.  Schematic geometry of the proposed antenna array

    图 9  仿真天线阵辐射性能 (a) |S11|; (b) 增益; (c) 5.8 GHz处xoz面辐射方向图; (d) 5.8 GHz处yoz面辐射方向图

    Figure 9.  Simulated radiation properties of proposed antenna array: (a) Reflection coefficients |S11|; (b) gain; two-dimensional radiation patterns at 5.8 GHz for (c) xoz plane; (d) yoz plane.

    图 10  电磁波垂直入射时天线阵单站RCS (a) x极化; (b) y极化

    Figure 10.  Simulated scattering properties of antenna array under normal incidence: (a) x-polarization; (b) y-polarization.

    图 11  电磁波斜30°入射时天线阵镜像双站RCS (a) x极化; (b) y极化

    Figure 11.  Simulated specular scattering properties of antenna array for incident angle of 30°: (a) x-polarized incidence; (b) y-polarized incidence.

    图 12  5.8 GHz处三维散射图 (a) x极化下金属板; (b) x极化下天线阵; (c) y极化下金属板; (d) y极化下天线阵

    Figure 12.  Three-dimensional scattering patterns of total RCS at 5.8 GHz under x-polarized incidence for (a) metal board and (b) antenna array; under y-polarized incidence for (c) metal board and (d) antenna array.

    图 13  阵列天线实物及测试配置图 (a) 天线阵实物; (b) 功分器; (c) 散射测试环境

    Figure 13.  Fabricated sample of antenna array and testing environment: (a) Sample; (b) one in two power divider RS2W2080-S and one in eight power dividers RS8W2080-S; (c) testing environment for scattering performance.

    图 14  实测天线阵的辐射特性 (a) |S11|; (b) 5.8 GHz处xoz面辐射方向图; (c) 5.8 GHz处yoz面辐射方向图

    Figure 14.  Measured radiation properties of antenna array: (a) Measured reflection coefficients |S11|; two-dimensional radiation patterns at 5.8 GHz for (b) xoz plane; (c) yoz plane.

    图 15  RCS减缩量 (a) 入射波垂直入射; (b) 入射波斜30°入射

    Figure 15.  RCS reduction in contract to metal board for incident angles of (a) 0° and (b) 30°.

    表 1  本文所设计的低散射微带天线阵与文献[1720]中的对比

    Table 1.  Comparison between this work and other antenna arrays in Ref. [17−20].

    阵列规模阵元间隔/$\lambda $天线阵尺寸大小天线阵相对带宽/%带内RCS减缩量RCS缩减相对带宽/%
    文献[17]2 × 20.691.38$\lambda $ × 1.38$\lambda $2.4无减缩122
    文献[18]2 × 20.642.40$\lambda $ × 2.40$\lambda $10.93 dB以上126
    文献[19]2 × 20.603.65$\lambda $ × 3.65$\lambda $11.05 dB以上93
    文献[20]2 × 20.901.80$\lambda $ × 1.80$\lambda $5.5无减缩69
    本文4 × 40.481.92$\lambda $ × 1.92$\lambda $6.96 dB以上59
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  • [1]

    李文强, 曹祥玉, 高军, 赵一, 杨欢欢, 刘涛 2015 物理学报 64 094102

    Li W Q, Cao X Y, Gao J, Zhao Y, Yang H H, Liu T 2015 Acta Phys. Sin. 64 094102

    [2]

    Jiang W, Zhang Y, Deng Z B, Hong T 2013 J. Electromagn. Waves 27 1077

    [3]

    姜文, 龚书喜, 洪涛, 王兴 2010 电子学报 38 2162

    Jiang W, Gong S X, Hong T, Wang X 2010 Acta Electronica Sinica 38 2162

    [4]

    Genovesi S, Costa F, Monorchio A 2014 IEEE Trans. Antennas Propag. 62 163

    [5]

    Landy N I, Sajuyigbe S, Mock J J, Smith D R, Padilla W J 2008 Phys. Rev. Lett. 100 207402

    [6]

    Lan J X, Cao X Y, Gao J, Cong L L, Wang S M, Yang H H 2018 Radioengineering 27 746

    [7]

    Zhang C, Cheng Q, Yang J, Zhao J, Cui T J 2017 Appl. Phys. Lett. 110 143511

    [8]

    Paquay M, Iriarte J C, Ederra I, Gonzalo R, Maagt P 2007 IEEE Trans. Antennas Propag. 55 3630

    [9]

    Zheng Y J, Gao J, Xu L M, Cao X Y, Liu T 2017 IEEE Antennas Wirel. Propag. Lett. 16 1651

    [10]

    Wang H B, Cheng Y J 2016 IEEE Trans. Antennas Propag. 64 914

    [11]

    Xu G Y, Hum S V, Eleftheriades G V 2018 IEEE Trans. Antennas Propag. 66 780

    [12]

    Jia Y T, Liu Y, Zhang W B, Wang J, Wang Y Z, Gong S X, Liao G S 2018 Opt. Mater. 8 597

    [13]

    Zheng Q, Guo C J, Ding J 2018 IEEE Antennas Wirel. Propag. Lett. 17 1459

    [14]

    杨欢欢, 曹祥玉, 高军, 刘涛, 马嘉俊, 姚旭, 李文强 2013 物理学报 62 064103

    Yang H H, Cao X Y, Gao J, Liu T, Ma J J, Yao X, Li W Q 2013 Acta Phys. Sin. 62 064103

    [15]

    Zheng Y J, Cao X Y, Gao J, Yuan Z D, Yang H H 2015 IEEE Antennas Wirel. Propag. Lett. 14 1582

    [16]

    Liu Y, Li K, Jia Y T, Hao Y W, Gong S X, Guo Y J 2016 IEEE Trans. Antennas Propag. 64 326

    [17]

    Joozdani M Z, Amirhosseini M K, Abdolali A 2016 Electron. Lett. 52 767

    [18]

    Su J X, Kong C Y, Li Z R, Yin H C, Yang Y Q 2017 Electron. Lett. 53 520

    [19]

    Kang X L, Su J X, Zhang H, Yang Y Q 2017 Electron. Lett. 53 1088

    [20]

    Zhang C, Gao J, Cao X Y, Xu L M, Hang J F 2018 IEEE Antennas Wirel. Propag. Lett. 17 869

    [21]

    孙慧峰, 邓云凯, 雷宏, 焦军军, 石力 2012 中国科学院研究生院学报 29 282

    Sun H F, Deng Y K, Lei H, Jiao J J, Shi L 2012 J. Graduate Sch. Chin. Acad. Sci. 29 282

    [22]

    李响 2017 硕士学位论文 (南京: 南京信息工程大学)

    Li X 2017 M. S. Thesis (Nanjing: Nanjing University of Information Science & Technology) (in Chinese)

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  • Received Date:  13 September 2018
  • Accepted Date:  30 October 2018
  • Available Online:  23 March 2019
  • Published Online:  01 March 2019

Novel design of microstrip antenna array with low scattering performance

    Corresponding author: Cao Xiang-Yu, xiangyucaokdy@163.com
    Corresponding author: Gao Jun, gjgj9694@163.com
  • Information and Navigation College, Air Force Engineering University, Xi'an 710077, China

Abstract: In this paper, the idea of electromagnetic surface (EMS) is introduced into the design of microstrip antenna array. The antenna element proposed in this paper is treated as an EMS element, whose reflection characteristics are taken into consideration in the process of antenna array design. Firstly, a rectangular patch antenna element is designed. Then, by cutting arc-shaped structure into a rectangular patch, another element is created to generate 180° ± 30° effective phase difference compared with original antenna element. As a consequence, 180° ± 30° effective phase difference is obtained from 5.5 GHz to 6.9 GHz for the y-polarized incidence. Meanwhile, for the x-polarized incidence, each of the two elements possesses high absorptivity over the operating frequency as a result of matching load. Besides, the two elements work in the same resonant mode and the same resonant frequency band when treated as radiators. In order to further explain the consistency in radiation and difference in reflection between the two structures, current distribution at 5.8 GHz is investigated in terms of radiation and reflection. Then, the two elements are arranged into a chessboard array to achieve the low scattering performance based on phase cancellation principle under the y-polarized incidence. Based on the absorption principle, the matching load is added to improve the scattering performance of the composite antenna array with the x-polarized incidence. Simultaneously, the proposed antenna array maintains good radiation characteristics due to the consistency between the radiation performances of the two elements. The corresponding antenna array is fabricated and tested. Simulated and measured results prove that the proposed antenna array also achieves good radiation performance. And a 6 dB radar cross section reduction is obtained from 5.6 to 6.2 GHz under the x polarization and from 5.5 to 7.0 GHz under the y polarization for the normal incident wave, implying 10.1% and 24% in relative bandwidth, respectively. In-band reflection suppression in the specular direction is demonstrated for an incident angle of 30° under both polarizations. The measured results are in good agreement with the simulated ones. Additionally, the approach proposed in this paper offers an effective way to deal with the confliction between radiation and scattering performance, and can also be applied to other kinds of antenna arrays.

    • 随着电子战的快速发展, 隐身领域成为各国争相研究的重要战略领域. 天线作为诸多作战平台上不可或缺的一部分, 其重要性不言而喻. 但天线作为目标系统的强辐射和散射源, 其自身的雷达散射截面(radar cross section, RCS)给隐身平台尤其是低可探测平台的RCS贡献很大[1]. 因此, 降低平台上天线自身的RCS迫在眉睫. 传统方法通过外形结构设计、涂覆吸波材料[24]等手段在一定程度上实现了RCS减缩, 但对天线的辐射性能有一定的影响. 电磁表面(electromagnetic surface, EMS)是一种影响电磁波传播特性的超薄界面, 其定义为纵向尺寸(剖面厚度)远小于波长, 横向尺寸(表面口径大小)处于亚波长到一个波长之间, 且对电磁波具有散射、透射或者吸收作用的周期或非周期人工结构. EMS所包含的范围非常广泛, 包括具有完美吸波特性的吸波体(metamaterial absorber)、具有同向反射特性的人工磁导体(artificial magnetic conductor, AMC)、具有空间滤波特性的频率选择表面(frequency selective surface, FSS)、具有极化转换特性的极化旋转表面(polarization rotation surface, PRS)等[513]. 随着EMS的发展, 其在减缩单个天线RCS上的成功应用[1416]也给减缩天线阵列RCS提供了参考.

      文献[17]通过采用带阻型FSS取代2 × 2天线阵的金属地板, 在4.0—16.5 GHz范围内有效降低了天线阵的RCS. 文献[18]通过利用多种单元构造新型的PRS, 并以共地板共基板的方式将其加载在2 × 2贴片阵列周围, 在保持辐射特性基本不变的情况下, 在6.0—7.6 GHz和9.5—26.0 GHz范围内实现了天线的RCS减缩. 文献[19]将有效相位差的EMS排布在2 × 2微带天线阵周围, 在6.2—7.3 GHz范围内有效减缩了天线RCS. 2018年, Zhang等[20]将两种AMC结构放置在微带天线阵下方, 并利用编码思想优化布阵, 在6.0—13.4 GHz宽带范围内实现了RCS减缩. 尽管已有较多文献通过加载EMS实现了天线阵的RCS减缩, 但在设计时, EMS单元和天线阵设计各自独立, 且所研究的对象大多偏向于小规模阵列, 对于更大规模阵列天线的RCS缩减问题研究较少.

      本文针对较大规模微带天线阵的辐射与散射难以同时兼顾的难题, 在设计天线单元时, 引入EMS的设计思想, 单元结构既作为天线单元, 又作为EMS单元. 在矩形贴片天线研究的基础上, 通过结构优化演变设计了另一种与原始天线单元工作在相同模式、相同频段的天线单元, 并与其形成有效相位差. 通过将两种单元以棋盘形式布阵组成4 × 4天线阵, 在y极化下, 实现了基于相位对消原理的RCS减缩, 在x极化下, 采用加载匹配负载的方式实现了基于吸波原理的RCS减缩. 由于两种天线单元在辐射性能上具有较好的一致性, 使得组合天线阵同样具有优良的辐射性能.

    2.   单元设计与分析
    • C波段微带天线已广泛应用于卫星通信、导航、气象勘察、无线电卫星定位等领域[21,22], 因此本文在基于有限元法的商用电磁仿真软件Ansoft HFSS中建模并设计了一个工作在5.8 GHz的微带天线. 单元结构如图1(a)所示, 天线单元大小p为25 mm (0.48$\lambda $, $\lambda $为5.8 GHz对应的波长), 介质板采用介电系数${\varepsilon _{\rm{r}}}$为2.65, 介质损耗$\tan {\delta _{\rm{r}}}$为0.001的聚四氟乙烯玻璃布板, 厚度t = 3.0 mm. 矩形贴片的长边l1 = 13.6 mm, 窄边w1 = 14.4 mm, 天线馈电点的位置离中心的距离s1 = 2.9 mm, 为便于描述, 该单元作为天线单元时称为E1.

      Figure 1.  Geometry of (a) element 1 and (b) element 2.

      在主从边界条件和Floquet端口激励下, 对单元1作为EMS1的反射特性进行仿真, 结果如图2所示. 在x极化下, EMS1加载$50\; \Omega $匹配负载后, 反射幅度大幅降低, 存在较高的吸波率, 其最小反射幅度对应频点接近E1的谐振点5.8 GHz. 在y极化下, 加载前后, EMS1反射幅度始终接近于1, 类似全反射, 反射相位没有变化. 由以上分析可知, 匹配负载的引入仅对x极化下的反射抑制有所改善, 而对y极化下的反射特性影响较小, 因此y极化下的全反射急需得到抑制. 在此基础上, 分析了加载匹配负载后, 不同参数对EMS1反射特性的影响, 结果如图3所示. 由图3(a)图3(b)可知, x极化波照射下, 随着l1的增加, 吸波频点逐渐向低频移动, 相位也随之向低频偏移, l1y极化下的反射幅度和相位影响很小. 据图3(c)图3(d)可知, 馈电位置s1x极化下的反射幅度影响较大, 相位影响较小, 对y极化下的反射幅度和相位影响均很小. 如图3(e)图3(f)所示, w1对两个极化下的反射幅度影响较小, 但对y极化下的反射相位影响却很大.

      Figure 2.  Reflection characteristics with and without matching load: (a) Reflection magnitude; (b) reflection phase.

      Figure 3.  Effects of various parameters on reflection performance: Effects of l1 on (a) reflection magnitude and (b) phase; effects of s1 on (c) reflection magnitude and (d) phase; effects of w1 on (e) reflection magnitude and (f) phase.

      根据以上分析, 为了使由两种单元组合的阵列在y极化入射波下实现基于相位对消原理的RCS减缩, 在矩形贴片上开口设计单元2是较好的方法, 其目的在于减小窄边w1y方向上的等效长度, 使y极化下的反射相位向高频移动, 从而与EMS1之间形成有效相位差. 故通过在矩形贴片上开弧形缺口, 分析开口对天线反射系数及对y极化入射波下反射相位的影响, 结果如图4所示. 由图4可知, 开口后天线相对带宽几乎不变, 工作频带稍向低频移动, 而在y极化下的反射相位则向高频移动, 故开口有利于相位向高频偏移以便与原始单元之间形成有效相位差. 之后通过优化天线矩形辐射贴片的长边、窄边及开口的深浅r和馈电点位置s2, 得到了既使E2与E1工作在相同频段, 又使EMS2在y极化下与EMS1存在有效相位差的最终结构, 如图1(b)所示. 具体参数如下: l2 = 12.0 mm, w2 = 14.3 mm, s2 = 2.3 mm, r = 3.8 mm.

      Figure 4.  Influences of arc-shaped structure on reflection coefficient |S11| and reflection phase.

      图5(a)给出了优化后两种天线的|S11|曲线, E2仍在5.8 GHz处谐振, 谐振带宽(5.2%)相较于E1 (6.9%)略有缩减. 图5(b)给出了在谐振点5.8 GHz的方向图, 二者无论是xoz面还是yoz面都近乎完全重合, 故E2与E1在辐射性能上具有较好的一致性. 当两种单元作为EMS时, 其对应的反射特性如图6所示. 在x极化下, 二者均存在较高的吸波率, 相位曲线差别不大, 不存在有效相位差. 而在y极化下, 都近乎全反射, 但在5.5—6.9 GHz存在有效相位差, 基本满足相位对消的条件.

      Figure 5.  Radiation properties of two elements: (a) Reflection coefficients |S11|; (b) two-dimensional radiation patterns at 5.8 GHz.

      Figure 6.  Reflection characteristics of two elements: (a) Reflection magnitude; (b) reflection phase.

      为了进一步说明这种开口方式的机理, 图7给出了两种单元在辐射边界条件下的表面电场分布和在主从边界条件下的表面电流分布. 由图7(a)图7(b)可知, E1辐射贴片两窄边电场方向相反, 开缺口后, E2窄边两端的电场方向仍互为反向, 天线的主模激励TM10模没有发生改变. 在y极化波照射下, EMS1和EMS2在各自零反射相位频点(5.24和6.86 GHz)的表面电流分布如图7(c)图7(d)所示, 由于EMS2金属贴片在y方向上的实际物理尺寸减小, 使电流流动路径变短, 因此EMS2的谐振频率向高频偏移, 从而与EMS1之间形成了有效相位差.

      Figure 7.  Surface E-field distributions at 5.8 GHz of (a) E1 and (b) E2; surface current distributions (c) at 5.24 GHz of EMS1 and (d) at 6.86 GHz of EMS2.

    3.   低散射微带天线阵的设计与分析
    • 采用2 × 2的单元块以棋盘布阵方式设计组合天线阵, 为便于描述, 对阵列中的天线单元进行编码, 具体编码方式如图8所示.

      Figure 8.  Schematic geometry of the proposed antenna array

      取阵列中间四个单元作为对比, 即取E22, E23, E32, E33. 图9(a)给出了这四个天线单元的|S11|, 可以看出, |S11|曲线几乎重合, 均在5.8 GHz产生谐振. 图9(b)给出了增益特性曲线, 可以看出, 阵列在工作频带内, 增益始终在16 dBi以上. 图9(c)图9(d)给出了在5.8 GHz的方向图, 可知在主瓣方向天线阵交叉极化远小于主极化. 以上分析验证了两种具有相同谐振模式, 且工作频带几乎相同的天线单元组合布阵后, 也拥有良好的辐射特性.

      Figure 9.  Simulated radiation properties of proposed antenna array: (a) Reflection coefficients |S11|; (b) gain; two-dimensional radiation patterns at 5.8 GHz for (c) xoz plane; (d) yoz plane.

      图10给出了天线阵列的单站RCS, 并与等大小金属板的RCS比较. 在入射波垂直入射时, x极化下, 天线阵在谐振点5.8 GHz处具有较强的反射抑制, 相较于金属板, 在5.6—6.2 GHz范围内实现了6 dB以上的RCS减缩, 覆盖天线工作频段5.6—6.0 GHz. y极化下, 天线阵在5.5—7.0 GHz范围内实现了6 dB以上的RCS减缩, 相对带宽为24%. 在入射波斜30°照射下的镜像双站RCS如图11所示, x极化下, 所设计的天线阵在带内仍可有减缩6 dB以上, y极化下, 在5.5—7.0 GHz仍有5 dB以上的RCS减缩.

      Figure 10.  Simulated scattering properties of antenna array under normal incidence: (a) x-polarization; (b) y-polarization.

      Figure 11.  Simulated specular scattering properties of antenna array for incident angle of 30°: (a) x-polarized incidence; (b) y-polarized incidence.

      为了直观地说明两种极化下RCS减缩的机理不同, 图12给出了在入射波垂直入射时5.8 GHz处不同极化下的三维散射方向图. 可以看出, 设计天线阵在x极化下的反射波峰明显小于金属板, 在整个角域内的能量都得到了降低, 故在x极化下的RCS减缩是基于匹配负载的吸收. y极化下, 设计天线阵在$\varphi $ = 45°, 135°, 225°和315°平面出现强散射峰, 散射能量被分散到四个对角线区域, 同时在鼻锥方向的反射能量较小, 说明在y极化下, 设计天线阵的RCS减缩是基于相位对消.

      Figure 12.  Three-dimensional scattering patterns of total RCS at 5.8 GHz under x-polarized incidence for (a) metal board and (b) antenna array; under y-polarized incidence for (c) metal board and (d) antenna array.

      基于以上分析可知, 设计天线阵具有较好的辐射和散射性能. 此外, 就本文所设计天线阵的辐散射性能和物理尺寸与其他文献[1720]中报道的低散射微带天线阵进行了比较, 结果如表1所列, 表中$\lambda $表示天线谐振点处对应的波长. 通过与已有文献相比可知, 本文所设计天线阵的规模相对较大, 阵元间隔较小; 单元组阵后, 阵列的尺寸相对较小; 能保持较好的辐射性能, 带内的散射性能同时得到了有效改善; 且采用了辐射散射一体化设计思想, 易于实现.

      阵列规模阵元间隔/$\lambda $天线阵尺寸大小天线阵相对带宽/%带内RCS减缩量RCS缩减相对带宽/%
      文献[17]2 × 20.691.38$\lambda $ × 1.38$\lambda $2.4无减缩122
      文献[18]2 × 20.642.40$\lambda $ × 2.40$\lambda $10.93 dB以上126
      文献[19]2 × 20.603.65$\lambda $ × 3.65$\lambda $11.05 dB以上93
      文献[20]2 × 20.901.80$\lambda $ × 1.80$\lambda $5.5无减缩69
      本文4 × 40.481.92$\lambda $ × 1.92$\lambda $6.96 dB以上59

      Table 1.  Comparison between this work and other antenna arrays in Ref. [17−20].

    4.   加工实测
    • 为了验证所设计天线阵的辐散射特性, 制作了天线阵的实物样件, 如图13(a)所示. 采用一个一分二的功分器与两个一分八的功分器相连接给每个天线单元进行馈电, 利用矢量网络分析仪(Agilent N5230C)在微波暗室中测试天线的辐射性能. 将两个1—18 GHz的喇叭天线分别作为收发天线, 与矢量网络分析仪相连, 用来测试天线阵的散射性能. 天线阵的散射测试环境如图13(c)所示, 泡沫作为支撑结构, 实物样件和喇叭处于同一水平线, 两喇叭之间放置吸波材料减小耦合.

      Figure 13.  Fabricated sample of antenna array and testing environment: (a) Sample; (b) one in two power divider RS2W2080-S and one in eight power dividers RS8W2080-S; (c) testing environment for scattering performance.

      图14给出了实测的天线阵|S11|和在5.8 GHz处的方向图. 可以看出, 阵列单元均谐振在5.8 GHz处, 谐振带宽相差较小, 实测辐射方向图与仿真方向图近乎重合, 设计的天线阵列具有良好的辐射性能. 图15(a)给出了天线阵在垂直入射时相较于等大小金属板的RCS减缩量. x极化下, 天线阵在天线工作频带内实现了6 dB以上的RCS减缩, 最大减缩量达13.8 dB. y极化下, 天线阵在5.3—7.1 GHz范围内实现了6 dB以上的RCS减缩. 在斜入射30°时, 实测的镜像双站RCS如图15(b)所示, 天线阵在任意极化波斜入射时, 仍具有良好的反射抑制特性. 实测结果验证了设计方法的有效性.

      Figure 14.  Measured radiation properties of antenna array: (a) Measured reflection coefficients |S11|; two-dimensional radiation patterns at 5.8 GHz for (b) xoz plane; (c) yoz plane.

      Figure 15.  RCS reduction in contract to metal board for incident angles of (a) 0° and (b) 30°.

    5.   结 论
    • 本文在设计微带天线阵时, 同时考虑其辐射性能和散射性能, 天线单元本身具有与EMS单元相似的物理结构, 故将天线单元同时作为EMS单元分析了其反射特性. 将两种工作在同一模式、同一频段的单元结构以棋盘布阵的形式构造4 × 4微带天线阵, 利用单元之间的有效相位差降低阵列天线的RCS, 仿真结果与实测结果验证了阵列的低散射特性. 本文的研究有效解决了微带天线阵辐射和散射难以兼顾的矛盾, 在阵列规模扩大时, 采用棋盘布阵方式仍可实现较好的RCS减缩效果, 同时为其他形式低散射天线阵的设计提供了一种新的思路.

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