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无源超高频射频识别系统路径损耗研究*
Analysis and measurments of path loss effects for ultra high frequency radio-frequency identification in real environments?
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摘要: 基于射频识别技术原理及Friis传输方程，导出了自由空间下无源超高频射频识别(RFID)系统路径损耗表达式.结合菲涅耳区理论，分析了菲涅耳余隙及阅读器天线至标签间距两因变量条件下第一菲涅耳区受阻隔对RFID系统路径损耗的影响，并提出了双斜率对数距离路径损耗模型.在开阔室内环境下，测试了菲涅耳余隙及阅读器天线至标签间距变化时的系统路径损耗.测试结果表明：菲涅耳余隙大于第一菲涅耳区半径1.5倍时，刃形障碍物对系统路径损耗影响较小；相比传统对数距离路径损耗模型，双斜率模型标准差减小10%.Abstract: Based on the principles of radio-frequency identification (RFID) technology and Friis propagation equation, the path loss ex-pression of ultra high frequency (UHF) RFID in free space is provided. The Fresnel clearance and horizontal interval between reader antenna and tag are employed as dependent variables, and then the obstructing effect of the first Fresnel zone on path loss is discussed. By the methods of linear regression and minimum mean-square error, a dual-slope Logarithm distance path losses model is proposed. The path losses of UHF RFID under different parameters are measured in open indoor environment. The measurement results indicate that RFID system experiences less fading when the Fresnel clearance is 1.5 times higher than the first Fresnel radius. The standard deviation of the proposed model with two slopes reduces ten percent or more compared with that of traditional logarithm distance path loss model.
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