칩 임피던스의 변화에 둔감한 특성을 갖는 RFID 태그의 설계

Abstract

Radio Frequency Identification (RFID) of objects has become very popular in logistics, inventory management and bio-engineering applications. To meet the need of the market, there has been intense research on RFID tag antennas in the UHF band, especially at 900㎒ because propagation characteristics for middle to long range wireless links are favorable at this frequency. Data transfer of passive RFID systems at UHF frequencies is based on backscattering. A tag antenna reflects back a part of the energy received from a reader. In that process, the reflected energy is modulated by the microchip of the tag. The chip impedances vary from company to company. The resistance is usually in the range of 3-80(Ω ) and the reactance, in the range of -270 to -80(Ω ). A good tag antenna structure must be conjugate matched to specific chip impedance with a simple adjustment of its dimensions and its impedance bandwidth has to be broad enough. Most of the developed tag antennas are a dipole shape or its similar ones. The mechanism of re-radiation from a dipole-shaped tag is well known [3]. However, its disadvantage is that the impedance bandwidth is narrow. Besides, the resistance and reactance cannot be controlled separately. So, we must develop insensitive tag for variation of chip impedance.

This thesis describes of printed dipole antenna for RFID tag and evaluates performance characteristics by material surface environments sticked RFID tag with printed dipole antennas. Designed antenna that generally using RFID tag a printed dipole antenna designed by FR4 substance. This antenna is assumed that it is sticked some products such as metal plate, dielectric material and ferrite material. It is evaluated performance of antenna characteristics as received signal value, radiation pattern and gain. When backside plane is metal, we confirmed that antenna performance is varied by backside plane.

Moreover, This thesis describes development of insensitive RFID tag independent about variation of chip impedance. Designed tag antenna is operated at 900 MHz bands, and its performance is maintained although reactance of the chip is changed. If chip reactance changes from ?j80 to -j270 ohm, this tag takes -10 dB bandwidth in 900 MHz bands. Moreover we confirmed that this tag antenna has ability to use commercial chip model.