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由于具有拓宽信道的能力, 携带轨道角动量的涡旋电磁波已经受到越来越多学者的研究. 目前, 基于反射式涡旋波发生装置仍然存在两个问题需要解决: 1) 馈源的遮挡; 2) 由馈源和反射表面所引起的交叉极化分量. 本文提出了一种基于超表面的偏馈式涡旋波产生装置, 该装置包括超表面反射阵和非正对区域放置的天线馈源. 本文主要贡献为以下三方面: 1) 设计了一种几何相位的超表面单元; 2) 主、交叉极化的转化过程被详细分析; 3) 具体的偏馈式涡旋波产生装置被设计. 通过合理设计超表面单元, 实现了仅对馈源主极化场的相位补偿与汇聚调控, 最终在期望的观测位置形成具有场增强效果的低交叉极化涡旋波. 仿真与实验分别验证了极化选择特性与汇聚涡旋波的形成. 该装置结构简单, 具有极化选择性和区域场增强效果, 对涡旋波通信及相关应用具有潜在价值.
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关键词:
- 超表面 /
- 涡旋波 /
- 偏馈 /
- Pancharatnam-Berry 相位
Orbital angular momentum, as a basic physical quantity of electromagnetic waves, has been widely studied since 1992. Recently, the geometric phase metasurface, which is also known as Pancharatnam-Berry (P-B) phase metasurface, has been proposed. Because of its frequency-independent and angle-dependent phase control characteristics, it can generate high-performance and broadband vortex wave. However, the current design of reflective metasurface encounters the following problems: 1) the reflected vortex wave is partly blocked by the feeding antenna; 2) in practical applications, the cross-polarized field will inevitably be induced due to the feed antenna and the reflective metasurface. How to avoid the cross-polarization is still worth further investigating. In this work, an offset-fed vortex wave generator is proposed. It consists of a right-handed circularly polarized Archimedes spiral antenna and a reflective metasurface. Firstly, the offset feeding design is introduced to avoid generating the cross-polarized fields caused by the feeding antenna. A geometric meta-atom of the reflective metasurface is designed at a working frequency of 8.5 GHz. By regularly arranging meta-atoms with different orientation angles, the convergence and phase compensation functions are imparted only to the co-polarization field. The cross-polarized field is intentionally weakened and refracted along other directions. Subsequently, a low cross-polarized vortex wave with an enhancement effect is obtained at the desired observation position. There are three contributions made in this work: 1) a P-B meta-atom is proposed to fabricate the reflective metasurface; 2) the conversion relationship between the co-polarized and cross-polarized field is studied from the initial state to the final state, and the four transformation processes are demonstrated in detail; 3) an offset-fed vortex wave generator is established which allows one to generate high-performance vortex beam with arbitrary OAM mode. The experimental results are in good agreement with those simulation results, proving the proposed method effective and feasible. The proposed design shows its advantages including simple structure, polarization selectivity, and regional field enhancement effect, which has great potential applications in vortex wave communication and OAM-based target detection.-
Keywords:
- metasurfaces /
- vortex wave /
- offset-fed /
- Pancharatnam-Berry phase
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图 1 偏馈式涡旋波产生装置工作示意图, 其中超表面单元的具体结构被放大显示
Fig. 1. The work schematic diagram of the offset-fed vortex wave generator, where the specific structure of the metasurface unit is also displayed.
图 2 在圆极化下激励下, 超表面单元在不同取向角下的反射谱 (a)同极化; (b)交叉极
Fig. 2. The reflection spectra for the meta-atom with different orientation angles under CP wave excitations: (a) Co-polarization; (b) corss-polarization.
图 3 超表面相位实现过程, 包括涡旋相位, 偏馈补偿相位, 汇聚补偿相位和最终的超表面相位
Fig. 3. The design process of metasurface phase including the vortex phase, the offset feed compensation phase, the convergence compensation phase, and the final metasurface phase.
图 4 四种转化过程的场路径描述 (a) 激励的交叉极化到交叉极化; (b) 激励的主极化到主极化; (c) 激励的交叉极化到主极化; (d) 激励的主极化到交叉极化
Fig. 4. Path description of field for the four transformation processes: (a) Excited cross polarization to cross polarization; (b) excited main polarization to main polarization; (c) excited cross polarization to main polarization; (d) excited main polarization to cross polarization.
图 5 三个具体案例被仿真并进行场采样对比(观测平面设置在z = 150 mm, 大小为100 mm × 100 mm) (a) 偏馈
${{\boldsymbol{r}}_{\rm{f}}} = [ - 8 p, 0, 8 p]$ , 有汇聚项$ {{\boldsymbol{r}}_{\rm{o}}} = {\rm{ }}\left[ {0, 0, 24 p} \right] $ ; (b) 偏馈$ {{\boldsymbol{r}}_{\rm{f}}} = \left[ { - 8 p, 0, 8 p} \right] $ , 无汇聚项$ {{\boldsymbol{r}}_{\rm{o}}} = {\rm{ }}\left[ {0, 0, \infty } \right] $ ; (c) 正馈$ {{\boldsymbol{r}}_{\rm{f}}} = \left[ {0, 0, 8 p} \right] $ , 有汇聚项$ {{\boldsymbol{r}}_{\rm{o}}} = \left[ {0, 0, 24 p} \right] $ Fig. 5. The sampling field for three specific cases (the observation plane at z = 150 mm, and the size 100 mm × 100 mm): (a) Offset reflector with convergence term; (b) offset reflector without convergence term; (c) forward reflector with convergence term.
图 6 实物照片 (a) 超表面正面; (b) 超表面背面; (c) 偏馈式涡旋波发生装置; (d) 暗室测量图
Fig. 6. The photograph of the specific generator and the fabricated metasurface: (a) The front view of the metasurface; (b) the back view of the metasurface; (c) the offset-fed vortex wave generator; (d) the measurement scene in anechoic chamber.
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[1] Allen L, Beijersbergen M W, Spreeuw R J C, Woerdman J P 1992 Phys. Rev. A 45 8185
Google Scholar
[2] Kim H, Park J, Cho S W, Lee S Y, Kang M, Lee B 2010 Nano Lett. 10 529
Google Scholar
[3] Thidé B, Then H, Sjöholm J, Palmer K, Bergman J, Carozzi T D, Istomin Y N, Ibragimov N H, Khamitova R 2007 Phys. Rev. Lett. 99 087701
Google Scholar
[4] Jiang X, Liang B, Cheng J C, Qiu C W 2018 Adv. Mater. 30 1800257
Google Scholar
[5] 郭忠义, 刘洪郡, 李晶晶, 周红平, 郭凯, 高隽 2020 物理学报 69 244301
Google Scholar
Guo Z Y, Liu H J, Li J J, Zhou H P, Guo K, Gao J 2020 Acta Phys. Sin. 69 244301
Google Scholar
[6] Liu K, Cheng Y, Gao Y, Li X, Qin Y, Wang H 2017 Appl. Phys. Lett. 110 164102
Google Scholar
[7] Herring R A 2011 Science 331 155
Google Scholar
[8] Bozinovic N, Yue Y, Ren Y, Tur M, Kristensen P, Huang H, Willner A E, Ramachandran S 2013 Science 340 1545
Google Scholar
[9] Yan Y, Xie G, Lavery M P J, Huang H, Ahmed N, Bao C, Ren Y, Cao Y, Li L, Zhao Z, Molisch A F, Tur M, Padgett M J, Willner A E 2014 Nat. Commun. 5 4876
Google Scholar
[10] Chen Y, Zheng S, Li Y, Hui X, Jin X, Chi H, Zhang X 2016 IEEE Antennas Wirel. Propag. Lett. 15 1156
Google Scholar
[11] Liu K, Liu H, Qin Y, Cheng Y, Wang S, Li X, Wang H 2016 IEEE Trans. Antennas Propag. 64 3850
Google Scholar
[12] Yang Y, Zhao Z, Ding X, Nie Z, Liu Q-H 2019 IEEE Trans. Antennas Propag. 67 140
Google Scholar
[13] Chen M L N, Jiang L J, Sha W E I 2019 IEEE Antennas Wirel. Propag. Lett. 18 477
Google Scholar
[14] Yang L J, Sun S, Sha W E I 2020 IEEE International Symposium on Antennas and Propagation and North American Radio Science Meeting Montréal, Québec, Canada, July 5–10, 2020 pp923−924
[15] Yu N, Genevet P, Kats M A, Aieta F, Tetienne J P, Capasso F, Gaburro Z 2011 Science 334 333
Google Scholar
[16] Yu S, Li L, Shi G, Zhu C, Zhou X, Shi Y 2016 Appl. Phys. Lett. 108 121903
Google Scholar
[17] Yu S, Li L, Shi G 2016 Appl. Phys. Express 9 082202
Google Scholar
[18] Jiang S, Chen C, Zhang H, Chen W 2018 Opt. Express 26 6466
Google Scholar
[19] Chen M, Li J J, Sha W 2016 J. Appl. Phys. 119 064506
Google Scholar
[20] Xu H X, Liu H, Ling X, Sun Y, Yuan F 2017 IEEE Trans. Antennas Propag. 65 7378
Google Scholar
[21] Ran Y, Liang J, Tong C, Li H 2018 Opt. Commun. 427 101
Google Scholar
[22] 李晓楠, 周璐, 赵国忠 2019 物理学报 68 238101
Google Scholar
Li X N, Zhou L, Zhao G Z 2019 Acta Phys. Sin. 68 238101
Google Scholar
[23] Yang L J, Sun S, Sha W E I 2020 IEEE Trans. Antennas Propag. 68 2166
Google Scholar
[24] Yang L J, Sun S, Sha W E I 2021 Adv. Opt. Mater. 9 2001711
Google Scholar
[25] Liu H, Xue H, Liu Y, Feng Q, Li L 2020 IEEE Access 8 126504
Google Scholar
[26] Zhang K, Yuan Y, Zhang D, Ding X, Ratni B, Burokur S N, Lu M, Tang K, Wu Q 2018 Opt. Express 26 1351
Google Scholar
[27] 李勇峰, 张介秋, 屈绍波, 王甲富, 吴翔, 徐卓, 张安学 2015 物理学报 64 124102
Google Scholar
Li Y F, Zhang J Q, Qu S B, Wang J F, Wu X, Xu Z, Zhang A X 2015 Acta Phys. Sin. 64 124102
Google Scholar
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