射頻辨識系統之後散射分析與量測
及其偵測方法之改進

在本篇論文中，我們討論了不同的反射係數對天線後散射場差的影響。並從實驗量測到的後散射場中得到了符合理論推導出來的結果。接著我們將此結果應用在新型射頻辨識標籤架構上,此架構具有兩根獨立天線,一根天線其阻抗與標籤匹配，達到最大能量轉移,另一根天線接上open 與 short這兩種負載以達到最大的後散射場差，而在這條件下後散射天線阻抗的設計，我們建議其虛部跟實部的比值能夠越小越好。此外，我們從Reader裡擷取從Tag回傳的訊號，並使用同調解調法來解調，雖然得到的結果比市面上採用的解調法好,但結果並不讓我們滿意。我們觀察到從讀取機本身結構而產生的高通濾波器會影響Tag回傳的訊號，導致訊號的失真造成解調的錯誤率提高。因此我們根據這高通效應，調整了解調的方法，最後經過模擬跟實際運用在tag回傳的訊號，結果顯示這方法可以降低解調的錯誤機率。

關鍵字

射頻辨識；高通濾波器；反射係數；同調偵測；後散射場

並列摘要

In this thesis, we discuss the influence of the reflection coefficient on the backscattered fields of the tag antenna. In addition, the measurement result of backscattered fields is consistent with the result calculated by theoretical analysis. Next, we apply the above results in a novel tag structure for RFID system. This novel structure contains two antennas: one is designed to match the tag IC for maximum power transfer, and the other is alternatively switching between “open” and “short” to achieve maximum difference between backscattered fields. Based on this fact, when designing the impedance of backscattering antenna, the ratio of the imaginary part to the real part is suggested to be as small as possible. Moreover, we extract the actual waveform backscattered from the tag and apply the coherent detection method. Although the detection result is better than the detection result adopted in commercial products, but it is not as good as expected. We found that the increase in the probability of false detection is a result of the high-pass filter inherent in the reader structure. According to this high-pass effect, we proposed a modified coherent detection method. Simulation and measurement results verify that the proposed modified coherent detection method can reduce the detection error probability.

並列關鍵字

Radio Frequency Identification (RFID) ； High pass filter ； Reflection coefficient ； Coherent detection ； Backscattered field

參考文獻

[1] H. Stockham, “Communication by Means of Reflected Power”, Proceedings of the IRE, pp 1196-1204, October 1948.

[5] J. Y. Chen, “Analysis and Measurement for RFID Detection”. Master Thesis of the Graduate Institute of Communication Engineering, National Taiwan University, July, 2006.

[7] Ukkonen, L, Sydanheimo, L, and Kivikoski, M. (2007) "Read range performance comparison of compact reader antennas for a handheld UHF RFID reader." IEEE Communications Magazine 45, (4) 24-31.

[8] S. Chiu, I. Kipnis, M. Loyer, J.Rapp, D. Westberg J. Johansson, P. Johansson, “A

900 MHz UHF Reader Transceiver IC,” IEEE J. Solid-State Circuits, Vol. 42, No 12, Dec. 2007.

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射頻辨識系統之後散射分析與量測及其偵測方法之改進

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