射頻辨識偵測之分析與量測

Abstract

在本篇論文中，對於射頻辨識 (RFID)系統中標籤回傳的信號，我們提出了兩種不同的偵測方法來解調：非同調偵測法與同調偵測法。在射頻辨識系統中，因為反射場的量比起環境產生的雜訊要小的多；所以在提出的同調偵測法之中，反射場的大小與相位都將被利用來解調變信號，如此讀取機的偵測能力將得以增加。 我們架設了一個反射場的量測系統，並用其來量測與分析在不同天線負載、不同傳送接收天線與不同傳送能量下反射場的辨識能力。我們模擬並量測真實射頻辨識系統的回傳信號，利用提出的兩種偵測識方法做辨識；同調偵測的表現會比非同調偵測好。除此之外，我們利用不同的阻抗值來做負載阻抗調變(Impedance loading)。在不同的負載阻抗與不同的標籤反射天線下，偵測回傳信號的能力將會有所區別。根據以上得到的結果，我們提出了一種新的標籤天線架構，用以增加標籤的辨識率。 另一方面，標籤天線阻抗與晶片阻抗之間的匹配狀態是標籤天線設計中一個很重要的課題。因此，在本論文的最後，我們設計實驗並進行量測，並利用得到的結果分析匹配狀態與反射信號振幅差距的關係。

In this thesis, we propose two detection methods for RFID system: the incoherent detection and the coherent detection. In the RFID system, the amount of the backscattered field is very small compared to the field introduced by the environment and we can increase the detection capability by considering both the magnitude and the phase information of the backscattered field, which is the basic principle of the coherent detection method. We construct a system for the measurement of the backscattered field of the RFID system. When discussing the detection capability, the effects of utilizing different types of antennas and adopting different transmitting power are investigated. We generate and measure the backscattered signal and the two detection methods proposed are used for the demodulation. The performance of the coherent detection is better than the incoherent detection. Besides, the effects on detection capability with different loading impedances are also discussed. In addition, the matching state between the tag antenna and the IC is another important issue in the design of the tag antenna. Therefore, the relation between the matching state and the level difference of the backscattered signal is also investigated.