一种UHF RFID阅读器终端可调谐圆极化天线研究

Analysis on Tunable Circularly Polarized Antenna for Applications of UHF RFID Reader Devices

本文理论和仿真研究一种基于铁氧体基板的应用于超高频(UHF)射频识别(RFID)阅读器终端的可调谐型圆极化天线。这种天线由上层印制有辐射贴片的介质板、中间铁氧体层以及下层印制有接地面的介质板构成。其中铁氧体层在外加磁场作用下能使常规微带天线提供圆极化的辐射特性。更重要的是,这种天线的圆极化工作频率可随外加磁场强度的变化而产生频移特性,从而可覆盖世界范围内的所有UHF RFID工作频率。本文首先理论分析这种天线实现圆极化以及频率可调谐的原理,然后通过仿真研究实现一种可工作在840 MHz至960 MHz频率范围内的微带天线,3-dB阻抗带宽为7 MHz。同时,这种天线的增益在?1.9 dBic至2.5 dBic范围内可调,且在阻抗带宽内具有能覆盖120?的3-dB轴比特性。

A tunable circularly polarized (CP) patch antenna based on ferrite substrate is discussed in this paper, for universal ultra-high-frequency (UHF) RF identification (RFID) applications. Such antenna is composed of top dielectric layer printed with rectangular radiation patch, middle ferrite layer, and bottom dielectric layer printed with ground plane. The ferrite layer under an applied dc magnetic bias provides the CP radiation characteristic. Most importantly, ferrite layer can tune arbitrarily the operating frequency band in a wide range covering all the worldwide operating frequency bands of UHF RFID, by adjusting the dc magnetic bias. Theoretical analysis on the reason to realize CP properties without perturbation for the radiation patch and the tunability of operating frequency are firstly presented. Numerical results demonstrate that the proposed antenna, can be arbitrarily operated from 840 to 960 MHz with a narrow impedance bandwidth of about 7 MHz, a tunable gain level ranged from ?1.9 to 2.5 dBic, and a wide 3-dB AR beamwidth of 120? over the impedance bandwidth.