UHF Band RFID Near Field Reader Antenna Research

Radio frequency identification (RFID) is a wireless and non-contact automatic identification technology, whose principle is using the space coupling characteristics of the radio frequency signal to achieve the identification of the stationary or moving objects automatically. RFID has tremendous potential in fields of logistics management, access control system, commerce and trade, anti-counterfeiting technology and so on, which is considered as one of the most important information technology of this century. China, the world’s important manufacturing base, has a broad RFID market. However, the domestic research is still in the stage of tracking the latest technology of the developed countries, so the in-depth study for RFID antenna is necessary.This paper is committed to study the latest technology of RFID antenna: UHF-band RFID near-field antenna, which is used in the area of the item-level. An electric-small Loop Antenna (C<λ/10) has in phase and uniform current distribution along its loop, which will produce a strong magnetic field along its axis, but the field falls rapidly when the tag is moved a short distance away from the antenna. Thus, the read distance is very short. If the antenna is an electrical-large loop antenna (C>λ), it will encounter a problem:the current distribution along the loop is not in phase and shifts to produce a change in sign of the current flow, which results the antennas produce relatively weak magnetic field on its axis. In order to solve the problem, in the third chapter, we proposed the segmented-resonant antenna structure to make the current along the loop remains approximately in phase and uniform. But the disadvantage of this method is the antenna needs a lot of lumped high-frequency capacitances, which greatly increased the cost of the antenna. In the fourth chapter of the paper, the segmented coupling near-field antenna is constructed to replace the lumped capacitance using distributed capacitance. We use two adjacent metal lines to form an overlapping part which will produce a capacitance. This capacitance is controlled by two key dimensions:overlapping part (θ), the gap between the two adjacent segmented lines (d), which can be used to adjust the value of the capacitance. In the last of the paper, we fabricated a UHF band (Europe standard) near-field antenna which used in pharmaceutical production line. The antenna has 15cm read range and 8cm read width. A good match can be reached between simulation and measured results. And the antenna has good read performance.The paper thanks to the project of UHF-band RFID reader antenna near-field design from Siemens LTD., China.