應用於多層印刷電路板之射頻辨識天線設計

Abstract

射頻辨識是當前熱門的無線通訊技術，而印刷電路板製造是目前非常成熟的產業，兩者的結合應用有可能推動彼此的發展。本研究即是探討將RFID技術應用於PCB的可能性。藉由理論分析、模擬與實作驗證此想法，然後根據電子標籤內建於印刷電路板時會遭遇的限制來規劃我們的設計，諸如尺寸限制、讀取距離要求與金屬線路的影響。本研究提出三種可能將電子標籤內建於印刷電路板的方式，並且選擇使用其中一種，即可結合晶片的微帶線饋入式槽線天線成為內建式電子標籤。其後進行內建式電子標籤的實作與量測，不論是否將其嵌入印刷電路板中，皆獲得接近30公分的最大讀取距離，這是使用黏貼式電子標籤所無法達成的成效。本研究亦對黏貼式與內建式電子標籤效能差異做深入的分析、量測與模擬驗證：發現黏貼式電子標籤貼附於金屬線路上會造成天線輸入阻抗強烈地改變，進而影響天線與晶片的阻抗匹配特性，因此讀取距離才會嚴重縮減；而內建式電子標籤嵌入印刷電路板中之後阻抗變化極微，對讀取距離的影響不大。

Radio frequency identification (RFID) is currently a popular technology, and printed circuit board (PCB) manufacturing is a mature industry. Combining RFID and PCB could benefit each other. The topic of this work is to find a way of applying the RFID technology to PCB and then to verify the idea by theoretical analysis, simulation, and experiment results in this work. We start by developing our design according to restrictions on size limit, read distance requirement, and effect of metal traces, etc., that may be encountered when we try to embed RFID tags in PCB. We also bring up three designs for embedded PCB tags, and then choose the one that combines the chip with a microstripline-fed slot antenna as the desired embedded PCB tag. Finally, we did measurements on the embedded RFID tag, and obtained a maximum read distance around 30 cm no matter lodged in PCB or not. Such a long distance can not be achieved by attaching tags directly on PCB. We also did in-depth analysis, experimental measurements, and simulation verification for both of the adhesive and embedded PCB tags to compare their differences of performance. We found that the severe change of input impedance is the major reason affecting the impedance matching between the conventional antenna and the chip when they are attached on PCB. And it decreases the read distance drastically. However, the input impedance change of our antenna is small, when the antenna along with the chip is embedded in PCB. Thereby, it has a slight influence on read distance.