The Design And Research Of A RFID Reader Antenna

Radio frequency identification (RFID) is a non-contact automatic identification technology. It completes the object identification and data exchange through the radio frequency signal. RFID has been widely used in many fields such as industrial, commercial and agriculture because it has a long identification distance, a fast identification speed and a capacity of multi objects identification. RFID is also considered to be one of the most promising application technologies. Antenna is the main equipment for radio frequency signal transmission and reception in RFID system and it has a big influence on the performance of RFID system. So the research of RFID antenna is of important theoretical and practical significance.This paper makes a main study of the ultra-high frequency (UHF) RFID reader antenna. Most of the UHF RFID antennas are loop antennas and it is inductive coupling between the reader and tag antennas. The reading distance of the antenna will increase with the increasing of the diameter of the loop. However, the reading distance of the antenna will stop increasing when the diameter of the loop increases to a certain degree, and there may be reading nulls. In order to improve the reading performance, a reader antenna with capacitive coupling is proposed which also has advantage in multi tags identification. The antenna in this paper is a microstrip patch antenna. The tags are activated by the strong electric fields nearby the antenna. The two patches are fed through Wilkinson power divider. The feed points are opposite which can enhance the electric field. A disadvantage of the microstrip antenna is a narrow bandwidth. We introduce slots to the patches to solve the problem. The slots will slightly disturb the current on the patches and influence the resonance frequency of the antenna. As a result, we get a wide bandwidth. The measured bandwidth is35MHz (897MHz-932MHz) under the condition of S11less than-10dB which covers the Chinese and FCC standards. The measured reading distance is160mm and there are no reading nulls between40mm and160mm. The antenna can read several tags at the same time. The measured results tally well with the simulated results. The antenna can meet the practical application demand.