臺灣博碩士論文加值系統

近年來，近場通訊系統的應用日趨廣泛，諸如超高頻近場射頻辨識系統、近距離無線通訊技術(NFC)。在近場通訊系統中，我們希望成功的設計天線，並優化系統的效能，因此收發兩端的天線耦合分析就變得很重要。本論文提出一個簡單的公式，可以計算近場通訊系統中傳送天線和接收天線之間的功率耦合係數(power coupling coefficient)。此公式的適用性不拘天線的種類、形式、尺寸、工作頻率；所需的資訊為收發兩端天線在該工作頻率下的三維遠場場形、天線之間的相對傾斜角度及距離。換言之，我們所提出的公式可視為遠場福利斯傳輸方程式(Friis transmission equation)在近場的類比。

為了驗證公式的準確性，我們先考慮幾種常用的天線，利用他們的場形標準式(close-form pattern)，將計算的近場耦合係數和全波分析模擬(HFSS)作比較。此外，我們也以超高頻近場射頻辨識系統為例，設計符合此應用的天線，並且比較量測、模擬、理論計算的結果。透過這些驗證，我們確認所提出的公式可以精準的算出近場功率耦合係數。在實驗中我們也發現了一些影響耦合程度的參數，諸如接收天線的阻抗匹配、發送天線的指向性。藉由提出的公式，我們還可以計算超高頻近場射頻辨識系統的讀取距離以及可靠度。因此，這篇論文提出的成果相信有助於應用在近場通訊系統。

Recently, near-field communication systems have been widely used in many applications such as the near-field UHF RFID item-level tagging, the Near Field Communication (NFC) device, and the mCoupons. To successfully design and optimize the near-field communication systems, it is important to investigate the near-field coupling between the transmitting and receiving antennas. In this thesis, a simple formula has been presented for computing the coupling coefficient between two antennas that are placed in the near field of each other. The choices of the two antennas are arbitrary, and all the information needed includes the corresponding normalized vector far-field patterns along with their relative orientations and the antenna spacing.
To verify the proposed formulation, the coupling coefficients in several near-field scenarios, including a practical near-field UHF RFID system, are computed and compared to those measured and full-wave simulated using Ansoft HFSS. They are all in good agreement. Additionally, it is shown that several factors may influence the coupling coefficient, such as the impedance matching of the receiving antenna and the directivity of the transmitting antenna. With the aid of the proposed formulation, the near-field read range and read reliability can be determined and the near-field coupling phenomena can be investigated. The results thus obtained may be useful in the near-field communication systems.

Contents
Abstract I
Contents III
List of Figures V
List of Tables VII

Chapter 1 Introduction 1
1.1 Motivation........................................................................................................1
1.2 Thesis Overview...............................................................................................3

Chapter 2 Near-Field Coefficient 5
2.1 Introduction………...........................................................................................5
2.2 Antenna Field Region……………………........................................................6
2.3 Antenna Coupling versus Longitudinal Displacement......................................7
2.3.1 Spherical Wave Expansions for the Coupling Coefficient....................9
2.3.2 Evaluation of the Spherical Wave Coefficients...................................12
2.3.3 Relative Orientations...........................................................................14
2.4 Antenna Coupling versus Transverse Displacement…...................................15
2.5 Summary……………………………………………......................................17

Chapter 3 Comparisons between the Formulation and HFSS Simulation 19
3.1 Introduction.....................................................................................................19
3.2 Side-by-Side, Parallel Half-Wave Dipoles......................................................19
3.3 Side-by-Side, Polarization-Mismatched Half-Wave Dipoles..........................22
3.4 Polarization-Matched Square Loop and Half-Wave Dipole............................23
3.5 Summary..........................................................................................................26

Chapter 4 Application in Near-Field UHF RFID System 27
4.1 Introduction…….............................................................................................27
4.2 Reader Antenna……………............................................................................30
4.3 Tag Antennas………………………...............................................................34
4.3.1 Folded Dipole with a Closed Loop…………………..........................34
4.3.2 Meander Circular Loop.......................................................................37
4.3.3 Microstrip-to-CPS Transition..............................................................39
4.4 Measurement Results……………...................................................................41
4.4.1 Coupling Coefficient versus Longitudinal Displacement....................43
4.4.2 Coupling Coefficient versus Transverse Displacement.......................45
4.5 Enhancement of Power Coupling Level……..................................................51
4.5.1 Impedance Matching of the Receiving Antenna………......................51
4.5.2 Directivity of the Transmitting Antenna……………..........................54
4.6 Practical Applications of Near-Field RFID Systems.......................................55
4.6.1 Near-Field Read Range………………………..………......................55
4.6.2 Read Reliability……………………………………...........................57
4.7 Summary…………………………………………..........................................60

Chapter 5 Conclusions 61
5.1 Summary of This Thesis……………….....………..………….…..................61
5.2 Future Works……………………………….......……………….....................62

Appendix 65
A.1 Coupling Quotient in Terms of Far-Field Patterns………………..................65
A.2 Series Expansions of Spherical Wave Functions……………….....................67
A.3 Orthogonality Relationship of Tesseral Harmonics………….......................70

References 73

References

[1]P. Harrop, “Near field UHF vs. HF for item level tagging,” IDTechEx article. Available:
http://www.eurotag.org/?Articles_and_Publications
[2]D. Desmons, “UHF Gen2 for item-level tagging,” presentation at RFID World 2006. Available:
http://www.impinj.com/files/Impinj_ILT_RFID_WORLD.pdf
[3]C. Ajluni, “Item-level RFID takes off,” RF Design magazine, Sep. 2006.
[4]S. Ortiz, Jr., “Is near-field communication close to success?” IEEE Computer Society, Vol. 39, pp. 18–20, Mar. 2006.
[5]J. Walko, “A ticket to ride,” IET Communications Engineer, Vol. 3, pp. 11–14, Feb.-Mar. 2005.
[6]C. Evans-Pughe, “Close encounters of the magnetic kind,” The IEE Review, Vol. 51, pp. 38–42, May 2005.
[7]S. Esko, K. Jouni, P. Juha, Y. Arto, and K. Ilkka, “Application of near field communication for health monitoring in daily life,” Engineering in Medicine and Biology Society, IEEE annual international conference, pp. 3246–3249, Aug. 2006.
[8]S. Dominikus and M. Aigner, “mCoupons: An application for near field communication (NFC),” Advanced Information Networking and Applications Workshops, 2007, AINAW’07. 21st International Conference, vol. 2, pp. 421–428, May 2007.
[9]G. A. Wright, “Magnetic resonance imaging,” IEEE Signal Processing, vol. 14, no. 1, pp. 118–125, Jan. 1997.
[10]K. Fotopoulou, B. W. Flynn, “Optimum antenna coil structure for inductive powering of passive RFID tags,” IEEE International Conference on RFID, pp. 71–77, Mar. 2007.
[11]P. Cole, “Coupling relations in RFID systems,” “Coupling relations in RFID systems II: Practical performance measurements,” white papers, 2003. Available: http://www.autoidlabs.org/publications/page.html
[12]H. Schantz, “A near-field propagation law and a novel fundamental limit to antenna gain versus size,” IEEE Antenna & Propagation Society International Symposium, vol. 3B, pp. 134–137, Jul. 2005.
[13]D. C. Yates, A. S. Holmes, and A. J. Burdett, “Optimal transmission frequency for ultralow-power short-range radio links,” IEEE Trans. Circuits Syst. I, vol. 51, no. 7, pp. 1405–1413, 2004.
[14]A. D. Yaghjian, “An overview of near-field antenna measurements,” IEEE Trans. Antennas Propagat., vol. AP–34, pp. 30–45, Jan. 1986.
[15]A. D. Yaghjian, “Efficient computation of antenna coupling and fields within the near-field region,” IEEE Trans. Antennas Propagat., vol. AP–30, pp. 113–128, Jan. 1982.
[16]R. F. Harrington, Time-harmonic electromagnetic fields, Wiley 2001, pp. 264–276.
[17]L. C. Andrews, Special functions of mathematics for engineers, 2nd edition, New York: McGraw-Hill, 1992, pp. 317–319.
[18]K. Finkenzeller, RFID handbook: Radio–frequency identification fundamentals and applications, 2nd Edition, Wiley, 2004.
[19]P. V. Nikitin, K. V. S. Rao, and S. Lazar, “An overview of near filed UHF RFID,” IEEE International Conference on RFID, pp. 167–174, Mar. 2007.
[20]K. Kurokawa, “Power waves and the scattering matrix,” IEEE Trans. Microw. Theory Tech, vol. MTT-13, no. 3, pp. 194–202, Mar. 1965.
[21]S. L. Chen, K. H. Lin, “A folded dipole with a close loop antenna for RFID applications,” IEEE Antenna & Propagation Society International Symposium, pp. 2281–2284, Jun. 2007.
[22]H. K. Ryu, J. M. Woo, “Size reduction in UHF band RFID tag antenna based on circular loop antenna,” Internal Conference on Applied Electromagnetics and Communications, Oct, 2005, pp. 1–4.
[23]Y. Qian, T. Itoh, “A broadband uniplanar microstrip-to-CPS transition,” Microwave Conf. Proc. APMC’ 97, vol. 2,pp. 609–612, 1997.
[24]A. Rahmati, L. Zhong, “Reliability techniques for RFID-based object tracking Applications,” IEEE Internal Conference on Dependable Systems and Networks (DSN’ 07), Jun. 2007, pp. 113–118.
[25]Industry Whitepaper, “RFID and UHF: A prescription for RFID success in the pharmaceutical industry,” 2006. Available: http://www.pharmaceuticalonline.com/uhf/RFIDUHFAPrescriptionforRFIDSuccess.pdf
[26]S. R. Aroor and D. D. Deavous, “Evaluation of the state of passive UHF RFID: An experimental approach,” IEEE Systems Journal, vol. 1, pp. 168–176, Dec. 2007.