| Radio frequency identification(RFID) technology is one of the ten most important technologies in twenty-first century. The backscatter modulated passive RFID system working at Microwave and UHF has become a hot spot in research and development for RFID products. Because the quality of RF front-end of reader can directly influence the performance of transceiver of RFID system, the research on RF front-end for 2.45 GHz passive RFID reader is of great importance.First, this dissertation introduces the RFID system components and analyzes the related principles. Then the paper researches on the reader antennas of the RFID system, and designs a 2.45 GHz circularly polarized square microstrip patch antenna with single-feed by the use of perturbation. Taking this as an antenna element of array, a parallel-feed microstrip planar array antenna is designed. The simulation results show that the VSWR of antenna less than 2, which the gain at 2.45 GHz can achieve more than 10 d B at its maximum, and the circular polarization of antenna can be realized.Secondly, this dissertation analyzes and compares the relative RFID standards within 2.45 GHz band and UHF band. On this basis, the dissertation researches and analyses of the transmitter circuit and receiver circuit of RF front-end for 2.45 GHz passive RFID reader in detail. The system is simulated with ADS2013 software, and the overall system structure of the RF front-end of I/Q modulator and demodulator on base of circulator architecture is given.Lastly, by using the commercial chips, the RF front-end circuits of 2.45 GHz passive reader is designed, which includes the power supply module, the LO oscillator, oscillator amplifier, I/Q modulator, I/Q demodulator, power amplifier and analog baseband circuits and so on, the LO is controlled by STC89C51, and the circuit schematic diagram and PCB are drawn with Altium Designer09 software. By the test, the output power of amplifier is up to 17.96 d Bm, and the receiving distance is longer than 1m. |
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