Design Of RF Front End For2.4Ghz RFID Reader

Radio frequency identification (RFID) technology is a non-contact automaticallyintelligent identification technology, which can identify the target and exchange usefulbidirectional data information via non-contact radio frequency between RFID readers andtransponders. Because of its advantages, such as non-contact, long working distance,suitable for harsh environment and effective moving target identification, RFIDtechnology has been widely used in many fields. With the concept of―the Internet ofthings" been put forward and the fast development of the research on RFID technologyand its wide application, especially the backscatter modulated RFID technology, theresearch on2.4GHz backscatter modulated RFID is of great importance.The components of RFID system and its related principles are introduced. On thebasis of that, the dissertation presents the research and analysis of the structures ofRFID reader’s frequency source, radio frequency transmitter circuit and receiver circuit,and then the system structure of RF Front-end on base of I/Q modulator and demodulatorare given. By using the commercial chips, the front-end RF circuits of the2.4GHz RFIDreader is designed, which includes the local frequency synthesizer, I/Q modulator,power amplifier, circulator, I/Q demodulator and analog baseband circuit and so on．Thesystem is simulated with ADS2008software. The circuit Schematic diagram and PCBare drawn with Protel99SE software.According the analysis of reader antennas of the RFID system, the dissertationdesigns a circular polarization broadband antenna suitable for2.4GHz RFID reader. Theantenna uses two-layer microstrip structure which is placed one upon another one tobroaden the bandwidth of it, two microstrip by coupling feed way. The simulationresults show that bandwidth with S11less than-10dB of the designed antenna canachieve18.95%, that the6-dB axial-ratio bandwidth can achieve15.59%and the gain at2.4GHz can achieve7.2dB, which means that the antenna has a satisfactory circularpolarization broadband characteristic.