基于RFID应用的微带线定向耦合器的设计

Design of microstrip directional couple based on RFID application

在传统微带线定向耦合器的设计中，由于耦合微带线的不均匀性及有不同的偶模和奇模相速度，导致耦舍器有较差的方向性。为研究满足无线射频识别（RFID）应用的耦合器，文章根据在耦合器的闲置耦合端口引入短路短截线线，使耦舍端口失配，大幅度提高耦合器的方向性的方法上，进一步研究改变短截线的结构尺寸，观察其对耦合器特性的影响，运用HFSS仿真软件进行频率扫描，给出设计优化的方法，确定短截线的最佳尺寸。运用这种技术设计了工作在2.3—2．5GHz的10dB微带线定向耦合器，并运用于无线射频识别阅读器，在频带范围内隔离度超过-50dB。

A conventional microstrip coupled-line directional coupler has inherent drawback of poor direction, caused by different modal phase velocity between even and odd mode in inhomogeneous dielectric material such as microstrip substrate. To meet the requirement of radio frequency identification （RFID） application, a method is proposed based on a short circuit stub in coupling port. The stub is introduced to make mismatch in coupling port to achieve high direction. Based on plenty of frequency sweep in HFSS software and data analysis, this paper gives a method on how to change the size of stub to get the high direction. A microstrip coupled-line directional coupler for the RFID reader with the frequency band of 2.3-2.5 GHz is proposed. The directional couple can obtain isolation of -50dB and coupling of -10 dB.