作者中心
专家审稿
责编办公
编辑办公
An Overview of Frequency Diverse Array Radar Technology
-
摘要: 频率分集阵(Frequency Diverse Array, FDA)雷达不同天线单元的发射载频存在微小的差异，从而带来了发射方向图距离角度时间依赖的特性，这一特性提供了FDA雷达新的信息和信号处理灵活度，也带了新的技术问题。该文综述了FDA天线技术及雷达应用的相关研究进展，并重点从雷达系统理论与工程应用的角度，着重分析了相干FDA雷达和正交FDA雷达两种体制的技术特点，指出FDA雷达在抗干扰、抗模糊中的应用优势，梳理了FDA雷达技术的难点和研究方向。Abstract: The carrier frequencies of array elements in a Frequency Diverse Array (FDA) radar are slightly distinguished, leading to a range-angle-time-dependent transmit beampattern. Thus, an FDA radar carries additional information in a certain range and provides more flexibility in signal processing and new technical issues. FDA is covered by scope of the general waveform diversity concept. This paper overviews the state-of-the-art FDA technology and its radar applications. From the viewpoint of the general radar system theory, we mainly introduce the coherent FDA and orthogonal FDA frameworks. The orthogonal FDA is also referred to as Multiple-Input Multiple-Output (MIMO) radar using FDA or FDA-MIMO radar. Key applications in anti-jamming and issues related with range ambiguity are addressed. We also outline the challenges in FDA radar applications and several interesting research topics.
-
图 1 电场强度随角度和时间的变化关系，R=3 km
Figure 1. Electric field intensity with respect to angle and time, R=3 km
图 2 电场强度随距离和角度的变化关系，R=[1.5 km, 4.5 km]
Figure 2. Electric field intensity with respect to range and angle, R=[1.5 km, 4.5 km]
图 3 不同角度方向对应的电场强度，R=3 km
Figure 3. Electric field intensity in different angles/directions, R=3 km
图 4 相控阵和FDA的辐射电场能量分布图的传播示意图
Figure 4. Radiated power distribution and propagation of electric field
图 5 脉冲体制发射-接收联合波束形成，Tp=1/
$\Delta $ fFigure 5. Joint tranmit-receive beamforming with pulsed FDA, Tp=1/
$\Delta $ f
图 6 脉冲体制发射-接收联合波束形成，Tp=1/(2
$\Delta $ f)Figure 6. Joint tranmit-receive beamforming with pulsed FDA, Tp=1/(2
$\Delta $ f)
图 10 运动平台FDA-MIMO雷达发射-接收2维域的功率谱分布示意图
Figure 10. Spectra distribution of signal in transmit-receive two-dimensional domain with FDA-MIMO radar mounted on moving platform
图 12 干扰机真实目标和假目标在发射-接收2维空间频率域的分布
Figure 12. Distribution of True and false targets in transmit-receive two-dimensional spatial frequency domain
表 1 3种体制发射方向图相关特性比较
Table 1. Comparion of characters related to transmit beampatterns of phased array, MIMO, and FDA
阵列体制 不同方向的时域响应 方向图的距离依赖性 发射方向图主瓣 天线发射增益 相控阵 各向同性 距离无关 稳定 M2 经典MIMO 各向异性 随距离变化，无规律 无 M FDA 各向异性 随距离变化，有规律 自动扫描 M 
下载: 导出CSV
-
[1] Antonik P, Wicks M C, Griffiths H D, et al.. Range-dependent beamforming using element level waveform diversity[C]. Proceedings of International Waveform Diversity & Design Conference, Orlando, USA, 2006: 140–144. [2] Antonik P, Wicks M C, Griffiths H D, et al.. Frequency diverse array radars[C]. Proceedings of 2006 IEEE Conference on Radar, Verona, NY, USA, 2006: 215–217. [3] Antonik P, Wicks M C, Griffiths H D, et al.. Multi-mission multi-mode waveform diversity[C]. Proceedings of 2006 IEEE Conference on Radar, Verona, NY, USA, 2006: 580–582. [4] Wicks M C and Antonik P. Frequency diverse array with independent modulation of frequency, amplitude, and phase[P]. USA, 7319427, 2008. [5] Wicks M C and Antonik P. Method and apparatus for a frequency diverse array[P]. USA, 7511665, 2009. [6] Antonik P. An investigation of a frequency diverse array[D]. [Ph.D. dissertation], University College London, 2009. [7] Calderbank R, Howard S D, and Moran B. Waveform diversity in radar signal processing: A focus on the use and control of degrees of freedom[J]. IEEE Signal Processing Magazine, 2009, 26(1): 32–41. DOI: 10.1109/MSP.2008.930414 [8] Wicks M C, Rangaswamy M, Adve R, et al. Space-time adaptive processin: A knowledge-based perspective for airborne radar[J]. IEEE Signal Processing Magazine, 2006, 23(1): 51–65. DOI: 10.1109/MSP.2006.1593337 [9] Baizert P, Hale T B, Temple M A, et al. Forward-looking radar GMTI benefits using a linear frequency diverse array[J]. Electronics Letters, 2006, 42(22): 1311–1312. DOI: 10.1049/el:20062791 [10] Secmen M, Demir S, Hizal A, et al.. Frequency diverse array antenna with periodic time modulated pattern in range and angle[C]. Proceedings of 2007 IEEE Radar Conference, Boston, MA, USA, 2007: 427–430. [11] Eker T, Demir S, and Hizal A. Exploitation of linear frequency modulated continuous waveform (LFMCW) for frequency diverse arrays[J]. IEEE Transactions on Antennas and Propagation, 2013, 61(7): 3546–3553. DOI: 10.1109/TAP.2013.2258393 [12] Cetintepe C and Demir S. Multipath characteristics of frequency diverse arrays over a ground plane[J]. IEEE Transactions on Antennas and Propagation, 2014, 62(7): 3567–3574. DOI: 10.1109/TAP.2014.2316292 [13] Eker T. A conceptual evaluation of frequency diverse arrays and novel utilization of LFMCW[D]. [Ph.D. dissertation], Middle East Technical University, 2011. [14] Huang J J, Tong K F, Woodbridge K, et al.. Frequency diverse array: Simulation and design[C]. Proceedings of 2009 IEEE Radar Conference, Pasadena, CA, USA, 2009: 1–4. [15] Huang J J, Tong K F, and Baker C J. Frequency diverse array with beam scanning feature[C]. Proceedings of 2008 IEEE Antennas and Propagation Society International Symposium, San Diego, CA, USA, 2008: 1–4. [16] Higgins T, Blunt S D, and Shackelford A K. Space-range adaptive processing for waveform-diverse radar imaging[C]. Proceedings of 2010 IEEE Radar Conference, Washington, DC, USA, 2010: 321–326. [17] Farooq J, Temple M A, and Saville M A. Application of frequency diverse arrays to synthetic aperture radar imaging[C]. Proceedings of 2007 International Conference on Electromagnetics in Advanced Applications, Torino, Italy, 2007: 447–449. [18] Farooq J, Temple M A, and Saville M A. Exploiting frequency diverse array processing to improve SAR image resolution[C]. Proceedings of 2008 IEEE Radar Conference, Rome, Italy, 2008: 1–5. [19] Jones A M and Rigling B D. Planar frequency diverse array receiver architecture[C]. Proceedings of 2012 IEEE Radar Conference, Atlanta, GA, USA, 2012: 145–150. [20] Sammartino P F and Baker C J. Developments in the frequency diverse bistatic system[C]. Proceedings of 2009 IEEE Radar Conference, Pasadena, CA, USA, 2009: 1–5. [21] Sammartino P F and Baker C J. The frequency diverse bistatic system[C]. Proceedings of 2009 International Waveform Diversity and Design Conference, Kissimmee, FL, USA, 2009: 155–159. [22] Sammartino P F, Baker C J, and Griffiths H D. Range-angle dependent waveform[C]. Proceedings of 2010 IEEE Radar Conference, Washington, DC, USA, 2010: 511–515. [23] Sammartino P F, Baker C J, and Griffiths H D. Frequency diverse MIMO techniques for radar[J]. IEEE Transactions on Aerospace and Electronic Systems, 2013, 49(1): 201–222. DOI: 10.1109/TAES.2013.6404099 [24] Wang W Q, Shao H Z, and Cai J Y. Range-angle-dependent beamforming by frequency diverse array antenna[J]. International Journal of Antennas and Propagation, 2012, 2012: 760489. [25] Wang W Q. Range-angle dependent transmit beampattern synthesis for linear frequency diverse arrays[J]. IEEE Transactions on Antennas and Propagation, 2013, 61(8): 4073–4081. DOI: 10.1109/TAP.2013.2260515 [26] Wang W Q and So H C. Transmit subaperturing for range and angle estimation in frequency diverse array radar[J]. IEEE Transactions on Signal Processing, 2014, 62(8): 2000–2011. DOI: 10.1109/TSP.2014.2305638 [27] Wang W Q. Phased-MIMO Radar with frequency diversity for range-dependent beamforming[J]. IEEE Sensors Journal, 2013, 13(4): 1320–1328. DOI: 10.1109/JSEN.2012.2232909 [28] Zhuang L, Liu X Z, and Yu W X. Precisely beam steering for frequency diverse arrays based on frequency offset selection[C]. Proceedings of 2009 International Radar Conference-Surveillance for a Safer World, Bordeaux, France, 2009: 1–4. [29] Zhuang L and Liu X Z. Application of frequency diversity to suppress grating lobes in coherent MIMO radar with separated subapertures[J]. EURASIP Journal on Advances in Signal Processing, 2009, 2009: 481792. DOI: 10.1155/2009/481792 [30] Xu Y H, Shi X W, Xu J W, et al. Beampattern analysis of planar frequency diverse array[J]. International Journal of RF and Microwave Computer-Aided Engineering, 2015, 25(5): 436–444. DOI: 10.1002/mmce.v25.5 [31] Xu J W, Liao G S, and Zhu S Q. Receive beamforming of frequency diverse array radar systems[C]. Proceedings of the 2014 XXXIth URSI General Assembly and Scientific Symposium, Beijing, China, 2014: 1–4. [32] Xu Y H, Shi X W, Xu J W, et al. Range-angle-dependent beamforming of pulsed frequency diverse array[J]. IEEE Transactions on Antennas and Propagation, 2015, 63(7): 3262–3267. DOI: 10.1109/TAP.2015.2423698 [33] 胡柏林, 廖桂生, 许京伟, 等. 前视阵频率分集雷达空时杂波特性研究[J]. 电子与信息学报, 2013, 35(11): 2693–2699. DOI: 10.3724/SP.J.1146.2013.00077Hu Bo-lin, Liao Gui-sheng, Xu Jing-wei, et al. Study on space-time character of clutter for forward-looking frequency diverse array radar[J]. Journal of Electronics&Information Technology, 2013, 35(11): 2693–2699. DOI: 10.3724/SP.J.1146.2013.00077 [34] 张福丹. 基于频率分集阵列的聚束SAR虚拟辐射源[J]. 太赫兹科学与电子信息学报, 2013, 11(3): 420–423, 434. DOI: 10.11805/TKYDA201303.0420Zhang Fu-dan. Virtual radiation source of a spotlight SAR based on frequency diverse array[J]. Journal of Terahertz Science and Electronic Information Technology, 2013, 11(3): 420–423, 434. DOI: 10.11805/TKYDA201303.0420 [35] Wang W Q. Frequency diverse array antenna: New opportunities[J]. IEEE Antennas and Propagation Magazine, 2015, 57(2): 145–152. DOI: 10.1109/MAP.2015.2414692 [36] 王文钦, 邵怀宗, 陈慧. 频控阵雷达: 概念、原理与应用[J]. 电子与信息学报, 2016, 38(4): 1000–1011. DOI: 10.11999/JEIT151235Wang Wen-qin, Shao Huai-zong, and Chen Hui. Frequency diverse array radar: Concept, principle and application[J]. Journal of Electronics&Information Technology, 2016, 38(4): 1000–1011. DOI: 10.11999/JEIT151235 [37] Wang Y B, Wang W Q, and Chen H. Linear frequency diverse array manifold geometry and ambiguity analysis[J]. IEEE Sensors Journal, 2015, 15(2): 984–993. DOI: 10.1109/JSEN.2014.2359074 [38] Wang W Q, So H C, and Shao H Z. Nonuniform frequency diverse array for range-angle imaging of targets[J]. IEEE Sensors Journal, 2014, 14(8): 2469–2476. DOI: 10.1109/JSEN.2014.2304720 [39] Wang W Q. Two-dimensional imaging of targets by stationary frequency diverse array[J]. Remote Sensing Letters, 2013, 4(11): 1067–1076. DOI: 10.1080/2150704X.2013.837228 [40] Wang Y B, Wang W Q, and Shao H Z. Frequency diverse array radar Cramér-Rao lower bounds for estimating direction, range, and velocity[J]. International Journal of Antennas and Propagation, 2014, 2014: 830869. [41] Wang Y B, Wang W Q, Chen H, et al. Optimal frequency diverse subarray design with Cramer-Rao lower bound minimization[J]. IEEE Antennas and Wireless Propagation Letters, 2015, 14: 1188–1191. DOI: 10.1109/LAWP.2015.2396951 [42] Wang W Q and Shao H Z. Range-angle localization of targets by a double-pulse frequency diverse array radar[J]. IEEE Journal of Selected Topics in Signal Processing, 2014, 8(1): 106–114. DOI: 10.1109/JSTSP.4200690 [43] Wang W Q. Subarray-based frequency diverse array radar for target range-angle estimation[J]. IEEE Transactions on Aerospace and Electronic Systems, 2014, 50(4): 3057–3067. DOI: 10.1109/TAES.2014.120804 [44] Gao K D, Shao H Z, Chen H, et al. Impact of frequency increment errors on frequency diverse array MIMO in adaptive beamforming and target localization[J]. Digital Signal Processing, 2015, 44: 58–67. DOI: 10.1016/j.dsp.2015.05.005 [45] Gao K D, Wang W Q, Chen H, et al. Transmit beamspace design for multi-carrier frequency diverse array sensor[J]. IEEE Sensors Journal, 2016, 16(14): 5709–5714. DOI: 10.1109/JSEN.2016.2573379 [46] Khan W, Qureshi I M, Basit A, et al. A double pulse MIMO frequency diverse array radar for improved range-angle localization of target[J]. Wireless Personal Communications, 2015, 82(4): 2199–2213. DOI: 10.1007/s11277-015-2342-1 [47] Khan W, Qureshi I M, and Saeed S. Frequency diverse array radar with logarithmically increasing frequency offset[J]. IEEE Antennas and Wireless Propagation Letters, 2015, 14: 499–502. DOI: 10.1109/LAWP.2014.2368977 [48] Khan W and Qureshi I M. Frequency diverse array radar with time-dependent frequency offset[J]. IEEE Antennas and Wireless Propagation Letters, 2014, 13: 758–761. DOI: 10.1109/LAWP.2014.2315215 [49] Khan W, Qureshi I M, Sultan K, et al. Properties of ambiguity function of frequency diverse array radar[J]. Remote Sensing Letters, 2014, 5(9): 813–822. DOI: 10.1080/2150704X.2014.969813 [50] Basit A, Qureshi I M, Khan W, et al. Beam pattern synthesis for an FDA radar with hamming window-based nonuniform frequency offset[J]. IEEE Antennas and Wireless Propagation Letters, 2017, 16: 2283–2286. DOI: 10.1109/LAWP.2017.2714761 [51] Chen B X, Chen X L, Huang Y, et al. Transmit beampattern synthesis for the FDA radar[J]. IEEE Antennas and Wireless Propagation Letters, 2018, 17(1): 98–101. DOI: 10.1109/LAWP.2017.2776957 [52] Wang Y X, Li W, Huang G C, et al. Time-invariant range-angle-dependent beampattern synthesis for FDA radar targets tracking[J]. IEEE Antennas and Wireless Propagation Letters, 2017, 16: 2375–2379. DOI: 10.1109/LAWP.2017.2718580 [53] Yao A M, Wu W, and Fang D G. Solutions of time-invariant spatial focusing for multi-targets using time modulated frequency diverse antenna arrays[J]. IEEE Transactions on Antennas and Propagation, 2017, 65(2): 552–566. DOI: 10.1109/TAP.2016.2633902 [54] Guo R J, Ni Y H, Liu H J, et al. Signal diverse array radar for electronic warfare[J]. IEEE Antennas and Wireless Propagation Letters, 2017, 16: 2906–2910. DOI: 10.1109/LAWP.2017.2751648 [55] Li Q, Huang L, Zhang P C, et al. Beampattern synthesis for frequency diverse array via reweighted l1 iterative phase compensation[J]. IEEE Transactions on Aerospace and Electronic Systems, 2018, 54(1): 467–475. DOI: 10.1109/TAES.2017.2735638 [56] Wang W Q, Dai M M, and Zheng Z. FDA radar ambiguity function characteristics analysis and optimization[J]. IEEE Transactions on Aerospace and Electronic Systems, 2017. DOI: 10.1109/TAES.2017.2785598 [57] Shao H Z, Li J C, Chen H, et al. Adaptive frequency offset selection in frequency diverse array radar[J]. IEEE Antennas and Wireless Propagation Letters, 2014, 13: 1405–1408. DOI: 10.1109/LAWP.2014.2340893 [58] Wang W Q. Cognitive frequency diverse array radar with situational awareness[J]. IET Radar,Sonar&Navigation, 2016, 10(2): 359–369. [59] Saeed S, Qureshi I M, Basit A, et al. Cognitive null steering in frequency diverse array radars[J]. International Journal of Microwave and Wireless Technologies, 2017, 9(1): 25–33. DOI: 10.1017/S1759078715001221 [60] Xu Y H, Shi X W, Li W T, et al. Flat-top beampattern synthesis in range and angle domains for frequency diverse array via second-order cone programming[J]. IEEE Antennas and Wireless Propagation Letters, 2015, 15: 1479–1482. [61] Xu Y H, Shi X W, Xu J W, et al. Range-angle-decoupled beampattern synthesis with subarray-based frequency diverse array[J]. Digital Signal Processing, 2017, 64: 49–59. DOI: 10.1016/j.dsp.2017.02.005 [62] Li W T, Hei Y Q, Shi X W, et al. Range-angle-dependent beamforming with FDA using four-dimensional arrays[J]. Signal Processing, 2018, 147: 68–79. DOI: 10.1016/j.sigpro.2018.01.016 [63] Xu J W, Lan L, Liao G S, et al.. Range-angle matched receiver for coherent FDA radars[C]. Proceedings of 2017 IEEE Radar Conference, Seattle, USA, 2017: 324–328. [64] Gui R H, Wang W Q, Cui C, et al. Coherent pulsed-FDA radar receiver design with time-variance consideration: SINR and CRB analysis[J]. IEEE Transactions on Signal Processing, 2018, 66(1): 200–214. DOI: 10.1109/TSP.2017.2764860 [65] Wang W Q. Overview of frequency diverse array in radar and navigation applications[J]. IET Radar,Sonar&Navigation, 2016, 10(6): 1001–1012. [66] Wang W Q. Moving-target tracking by cognitive RF stealth radar using frequency diverse array antenna[J]. IEEE Transactions on Geoscience and Remote Sensing, 2016, 54(7): 3764–3773. DOI: 10.1109/TGRS.2016.2527057 [67] Qin S, Zhang Y D, Amin M G, et al. Frequency diverse coprime arrays with coprime frequency offsets for multitarget localization[J]. IEEE Journal of Selected Topics in Signal Processing, 2017, 11(2): 321–335. DOI: 10.1109/JSTSP.2016.2627184 [68] Turhaner A, Demir S, and Hizal A. Monopulse direction finding for linear frequency modulation based frequency diverse array[C]. Proceedings of 2017 IEEE Radar Conference, Seattle, WA, USA, 2017: 89–94. [69] 郑昱. 基于频率分集阵列的波束形成研究[J]. 现代雷达, 2015, 37(8): 29–32, 36. DOI: 10.16592/j.cnki.1004-7859.2015.08.007Zheng Yu. A study on the beam forming of frequency diverse array[J]. Modern Radar, 2015, 37(8): 29–32, 36. DOI: 10.16592/j.cnki.1004-7859.2015.08.007 [70] 张昭建, 谢军伟, 李欣, 等. 频率分集阵列的有源假目标鉴别方法[J]. 国防科技大学学报, 2017, 39(4): 69–76. DOI: 10.11887/j.cn.201704011Zhang Zhao-jian, Xie Jun-wei, Li Xin, et al. Deceptive jamming suppression and discrimination based on frequency diversity array[J]. Journal of National University of Defense Technology, 2017, 39(4): 69–76. DOI: 10.11887/j.cn.201704011 [71] 吴旭姿, 刘峥, 谢荣. 基于俯仰频率分集技术的波束形成方法[J]. 电子与信息学报, 2016, 38(12): 3070–3077. DOI: 10.11999/JEIT160667Wu Xu-zi, Liu Zheng, and Xie Rong. Beamforming with vertical frequency diverse array[J]. Journal of Electronics&Information Technology, 2016, 38(12): 3070–3077. DOI: 10.11999/JEIT160667 [72] 王伟伟, 吴孙勇, 许京伟, 等. 基于频率分集阵列的机载雷达距离模糊杂波抑制方法[J]. 电子与信息学报, 2015, 37(10): 2321–2327. DOI: 10.11999/JEIT150187Wang Wei-wei, Wu Sun-yong, Xu Jing-wei, et al. Range ambiguity clutter suppression for airborne radar based on frequency diverse array[J]. Journal of Electronics&Information Technology, 2015, 37(10): 2321–2327. DOI: 10.11999/JEIT150187 [73] 许京伟, 廖桂生. 前视阵FDA-STAP雷达距离模糊杂波抑制方法[J]. 雷达学报, 2015, 4(4): 386–392. DOI: 10.12000/JR15101Xu Jing-wei and Liao Gui-sheng. Range-ambiguous clutter suppression for forward-looking frequency diverse array space-time adaptive processing radar[J]. Journal of Radars, 2015, 4(4): 386–392. DOI: 10.12000/JR15101 [74] Liu Y M, Ruan H, Wang L, et al. The random frequency diverse array: A new antenna structure for uncoupled direction-range indication in active sensing[J]. IEEE Journal of Selected Topics in Signal Processing, 2017, 11(2): 295–308. DOI: 10.1109/JSTSP.2016.2627183 [75] Wang C H, Xu J W, Liao G S, et al. A range ambiguity resolution approach for high-resolution and wide-swath SAR imaging using frequency diverse array[J]. IEEE Journal of Selected Topics in Signal Processing, 2017, 11(2): 336–346. DOI: 10.1109/JSTSP.2016.2605064 [76] Li X X, Wang D W, Ma X Y, et al. FDS-MIMO radar low-altitude beam coverage performance analysis and optimization[J]. IEEE Transactions on Signal Processing, 2018. DOI: 10.1109/TSP.2018.2815011 [77] Xu J W, Zhu S Q, and Liao G S. Range ambiguous clutter suppression for airborne FDA-STAP radar[J]. IEEE Journal of Selected Topics in Signal Processing, 2015, 9(8): 1620–1631. DOI: 10.1109/JSTSP.2015.2465353 [78] Xu J W, Liao G S, and So H C. Space-time adaptive processing with vertical frequency diverse array for range-ambiguous clutter suppression[J]. IEEE Transactions on Geoscience and Remote Sensing, 2016, 54(9): 5352–5364. DOI: 10.1109/TGRS.2016.2561308 [79] Xu J W, Liao G S, Zhang Y H, et al. An adaptive range-angle-Doppler processing approach for FDA-MIMO radar using three-dimensional localization[J]. IEEE Journal of Selected Topics in Signal Processing, 2017, 11(2): 309–320. DOI: 10.1109/JSTSP.2016.2615269 [80] Xu J W, Liao G S, Huang L, et al. Robust adaptive beamforming for fast-moving target detection with FDA-STAP radar[J]. IEEE Transactions on Signal Processing, 2017, 65(4): 973–984. DOI: 10.1109/TSP.2016.2628340 [81] Xu J W, Liao G S, Zhu S Q, et al. Joint range and angle estimation using MIMO radar with frequency diverse array[J]. IEEE Transactions on Signal Processing, 2015, 63(13): 3396–3410. DOI: 10.1109/TSP.2015.2422680 [82] Xu J W, Liao G S, Zhu S Q, et al. Deceptive jamming suppression with frequency diverse MIMO radar[J]. Signal Processing, 2015, 113: 9–17. DOI: 10.1016/j.sigpro.2015.01.014 [83] Xu J W, Xu Y H, and Liao G S. Direct data domain based adaptive beamforming for FDA-MIMO radar[C]. Proceedings of 2016 IEEE Statistical Signal Processing Workshop, Palma de Mallorca, Spain, 2016: 1–5. -
图(12) / 表(1)
计量
- 文章访问数: 6486
- HTML全文浏览量: 2694
- PDF下载量: 1106
- 被引次数: 0
