射頻識別標籤之新型架構設計與分析

Abstract

在本篇論文中，我們提出了一款新型射頻辨識標籤架構，其天線構接方式與負載阻抗(Loading impedance)設計與傳統標籤不同。傳統標籤僅以一天線進行接收與傳送，無法得到最大後向散射差值(Backscattering level difference)且在不匹配狀態期間無法接收能量，為了解決傳統標籤的問題，我們提出新型標籤架構，其使用兩支各自獨立天線進行傳送與接收。一天線專責接收，其阻抗與標籤匹配，具有最大能量轉移，另一天線經由最佳負載阻抗(Loading impedance)設計，使其具有最大後向散射差值，進而提升偵測效能。 我們建立了一散射場量測系統，藉由該系統對新型標籤架構性能進行驗證與分析，並與傳統標籤進行效能比較，其實驗結果驗證新型標籤性能優於傳統標籤且符合理論分析，新型標籤偵測效能相較傳統標籤可提升6dB，預期此新型架構將可大幅提升讀取距離。 另外，對緊密排列的標籤天線陣列而言，標籤天線之間互耦合(Mutual coupling)效應對射頻辨識系統效能造成的影響是重要的問題，這種標籤天線之間的交互影響可能造成能量接收降低與某些標籤無法被讀取，因此，我們探討互耦合效應及其對射頻辨識系統特性的影響，藉由量測與模擬分析電氣與幾何上的變化對標籤讀取性能的影響，進而提出可行之解決方案。

In this thesis, we propose a novel structure of tag for RFID system. The way of antennas configuration and loading impedance design are different from conventional tags. The conventional tag has only one antenna, which is used for both receiving and scattering. The antenna is designed to match tag IC for receiving and switched between match state and mismatch state for backscattering. With this design, the maximum backscattering level difference cannot be obtained and also no power is supplied to the tag during the mismatch state. To simultaneously solve the above two problems, we propose a novel tag structure. The novel structure contains two independent antennas. One antenna is for receiving that is designed to match the tag IC for maximum power transfer. The other is for scattering. The scattering antenna is alternatively connected to two optimized impedance states for maximum backscattering level difference. With this new structure it is expected that the reading range can be much increased. We construct a system for measuring the backscattering field. We measure the backscattered signal and compare the detection performance. Experimental results show that performance obtained by the novel structure is 6dB better than that of the conventional tag. In addition, mutual coupling is an important problem for tag antennas. This type of interaction may reduce energy received and result in the failure of tag detection. Therefore, we investigated the effect of mutual coupling on RFID performance. By measurements and simulations, we can analyze the impact of electrical and geometrical variables on readability of the tag and try to provide a feasible solution.