Research Of RFID Tag Antenna Suitable For Multi-application Environment

RFID (Radio Frequency Identification) is a rising auto-identification technology. RFID systems achieve auto-identification and data-gathering of the object to be identified by utilizing space coupling of radio frequency signal to conduct two-way transmission of signals. A typical RFID system consists of a reader and an electronic tag.In terms of operation frequency, RFID systems can be divided into four categories: low frequency (LF), high frequency (HF), ultra high frequency (UHF), and microwave. UHF RFID systems have the largest market potentials, but are also the most difficult to implement. According to power supply, there are two different types of electronic tags: active and passive. Passive UHF RFID tags have the advantage of long read/write range, high data rate, low cost, and they are suitable for mass production. Therefore, passive UHF RFID systems are focus of the research in RFID.Design of tag antenna is one of the key issues in design of FRID system. Quality of antenna design largely decides the performance of the RFID system, especially the read/write rage. Designing an appropriate tag antenna and achieving impedance match between the antenna and the IC is not only the most important but also the most difficult part of RFID system design. Another challenge in antenna design is the affect of environment: when there is water of metal in the vicinity of the antenna, the field distribution nearby the antenna will be severely intervened; the resonance frequency and gain of the antenna will also be affected. When the affect comes to worst, the antenna might be unable to work.This paper presents a design of RFID tag antenna suitable for multi-application environment which operates at 915MHz. It is a rectangular microstrip patch antenna with hemisphere radiation pattern. The ground plane of the microstrip antenna shields the field in the backward, and therefore partly eliminates the affect of background. Quarter-wavelength radiation patch with shorting wall is chosen to reduce size of the antenna. FR4 is used for dialect substrate for cost reason. The tag IC is fed by embedded microstrip feed line and T-shape impedance-matching network is used for impedance matching. The radiation patch, feed line, and the impedance-matching network are a coplanar structure which can be etched simultaneously; this helps to simplify the manufacturing process.The antenna presented in this paper has been fabricated and tag IC is mounted to become a complete RFID tag. After practical testing with a reader, we get thatread/write range of the adjusted tag can reach more than 50 centimeters. The tag canwork properly in multi-application environment which includes water, metal,dielectrics. The antenna design fully meets all application needs.