RFID를 위한 다중편파 안테나 시스템 설계 및 구현

Design & Implementation of the Multiple Polarization Antenna System for RFID

This paper presented polarization reconfigurable RFID reader antenna operating at UHF band. The proposed reader antenna consists of microstrip antenna with dual feed networks, two SPDT switches, a SP4T switch and 3dB hybrid coupler. Polarization selective circuit located at the back of ground plane for minimizing effect on antenna. Fixed phase shifter and impedance matching circuit were added for compensation mismatching and phase difference between two feeding posts. The switching voltage is controlled by low & high voltage using ATmega128. Through control of voltage of switches, the proposed reader antenna can select horizontally linear polarization, vertically linear polarization, left-hand circular polarization (LHCP) and right hand circular polarization (RHCP). The proposed reader antenna satisfied 2:1 VSWR at 881MHz~952MHz with horizontally linear polarization and 873MHz~959MHz with vertically linear polarization. And the axial ratio of antenna measured under 3dB at UHF RFID band with circular polarization. The proposed antenna can select appropriative polarization due to user environment and polarization of tag antenna. So it can minimize PLF (Polarization Loss Factor) and improve inrerrogation range about 1.5m to up to 3m.