基于电容加载的UHF-RFID近场长天线设计

UHF-RFID Near-Field Long Antenna Based on Capacitance Loading

针对近场长天线的电流相位分布空间跨度大这一难点,设计了一款基于多电容加载的超高频(Ultra-high frequency,UHF)频段近场长天线。通过对长度为250mm微带传输线在间隔48.8mm处分段加载1.6pF电容,利用电容对电流的相位补偿作用改善了天线近场均匀性。在端口增加金属匹配枝节及负载电阻进行阻抗匹配。仿真及实测表明,该长天线回波损耗在918~933 MHz频段内低于-10dB,长天线正上方300mm处近场场强差值最大仅为3.2dB,天线正上方不同位置处最大读取距离差值波动不超过95mm,验证了该天线良好的近场均匀性。搭建射频识别(Radio frequency identification,RFID)系统并进行测试,进一步验证该款长天线在近距离RFID系统中的实用性。

The spatial span of the current phase distribution of near-field long antenna is large. To solve the difficult problem, an ultra-high frequency （UHF） near-field long antenna based on capacitance load- ing is designed in this paper. By dividing microstrip transmission line of 250 mm in length into several segments and loading capacitances of 1.6 pF in each 48.8 mm of the patch, the phase of electric current can be compensated. Metal branches and resistance are adopted in port to realize impedance matching. Simulation and research show that the return loss is below -10 dB between 918-933 MHz, the max difference of electric field is only 3.2 dB in 300 mm above the antenna, and the maximum difference of read distances in different positions is below 95 ram. The results show that the antenna is of good near electric field uniformity. The antenna is also measured in the radio frequency identification （RFID） system and the practicality is verified in near field application.