标签密集环境下天线互偶效应研究

基于射频识别技术原理及Friis传输方程, 导出了无源超高频射频识别系统链路模型, 结合二端口网络分析方法, 导出了标签密集环境下的标签天线互阻抗计算表达式.利用单阅读器单标签时的标签阻抗匹配条件, 基于功率传输系数及调制因子, 分析了互偶效应对系统链路的影响.在开阔室内环境中, 测试了双标签及标签单、双平面布置情形下的阅读器天线最小发射功率及系统识别率.测试结果表明, 双标签及双平面情形下, 阅读器天线最小发射功率变化率分别为(-7%, 11.6%)及(-10%, 12.5%).关键词：射频识别密集环境互偶效应互阻抗

Theory and measurement for mutual coupling effect of ultra high frequency radio-frequency identification in dense environments

The close displacement of ultra high frequency radio-frequency identification (UHF RFID) tags can be considered as an electromagnetically interconnected system which causes the mutual coupling effect among antennas of tags, thereby resulting in change in impedance matching condition. Based on the principles of RFID technology and Friis propagation equation, a link budget model of UHF RFID is provided which consists of one reader and one tag. Expressions of mutual impedance in dense environments are derived by using a two-port network. Utilizing the parameters of power transmission coefficient and modulation factor, the variation of system performance is discussed in theory and tested by three experiments which are conducted in open indoor environment. The measurement results show that the change rate of minimum power transmitted by the reader antenna is in a range from -7% to 11.6% for two-tag scene and from -10% to 12.5% for two-plane arrangement.