Research On Key Techniques Of Long-range Radio Frequency Identification System

Radio frequency identification is a kind of contactless automated identification technology. It has the advantages of large volume of data, good security, strong anti-interference capability and is widely used in industrial automation, commercial automation, transportation management and many other fields. UHF, microwave RFID system with fast read-write speed, high recognition rate and long recognition distance has got attention all over the world and become the focus of RFID technology. In China, low frequency RFID technology is already mature, but UHF, microwave RFID technology is still in the experimental stage and is only tested in government departments such as railway department and customs. To solve the above problems and practical scientific research tasks, the paper mainly studies the key technologies of long-range radio frequency identification system. The content can be divided into five parts.Passive UHF RFID system is complex, expensive and currently at the initial development stage in China. This paper has developed a low-IF and zero IF structure passive UHF RFID systems. The system with stable performance, low cost meets ISO18000-6B protocols and has passed the detection of national correlation department. The system has value to popularize.RF transmitter and receiver circuits of passive UHF RFID systems work on the same frequency at the same time, thus TX-to-RX isolation is still very difficult to overcome. The traditional isolation method will lead to increased hardware cost. This paper presents two kinds of measures to overcome TX-to-RX interference. First, based on traditional directional coupler, two stubs coupling-line directional coupler is proposed and designed. The coupler can greatly improve isolation, lower reader cost. Combining with defected ground structure, the size of directional coupler can be further reduced. In addition, the theory of multi-carrier passive UHF RFID system is analyzed and derived in detail, which offers some novel methods to improve TX-to-RX isolation of passive UHF RFID and has great improtance.Another major operating frequency of long-range RFID system is5.8GHz, and the typical application is dedicated short range communication system. According to that microwave RFID system equipments mainly relied on imports, this paper firstly developed a set of inexpensive microwave RFID systems for dedicated short-range communications, which meets domestic newest ETC standard-GB/T20851-2007. Then two planar antennas for microwave RFID systems are designed. A novel double-cruciform slot is proposed and applied on the microstrip YAGI antenna, which solves the problem traditional microstrip YAGI antenna has larger size. Combining substrate integrated waveguide technology, a compact SIW slot antenna is developed. The proposed antenna has the advantages of high gain and small size.Ultra-wideband (UWB) RFID technology is a new long-range RFID technology and still in the theoretical study stage. In this paper, ultra-wideband band-pass filter in the UWB RFID system is researched and designed. The equivalent circuit model and transmission characteristics of traditional DGS unit, semicircle DGS unit and semicircle SISS unit are analyzed and simulated. Based on three-line microstrip line structure, a novel UWB filter with wide stopband is designed. Combining open load and spiral slot, a UWB filter with notch band and wide stopband is designed. The designed filters with small size and low cost can effectively suppress narrowband interference and high-order harmonics.As RFID technology promoting, a number of tags or readers are frequently located in same region simultaneously. The interferences between adjacent tags and readers will affect the performance of long RFID system. Firstly, a variety of coding methods of RFID system are analyzed and simulated in this paper and encoding conditions selected by RFID system is confirmed. Then the binary tree search anti-collision algorithm is successfully realized in passive UHF RFID system. Finally, a new reader anti-collision algorithm is proposed in this paper which can reduce conflict and improve system efficiency.