Recent years, the research and application of Radio Frequency Identification (RFID) technology develop quite fast, especially UHF band backscatter modulation RFID technology. This paper studies key components of UHF band RFID systems, which includes reader, tag and relevant antennas. The major content of this paper is as follows.First, this paper analyses the operating mechanism and characteristics of backscatter RFID reader and tag, the organization of transmission and receiver module; proposes one simple and lost-cost multi-channel direct detection circuit in order to replace common IQ mixing receiver in RFID readers. Besides, this paper describes methods for measuring impedances and antennas of RFID tags.Second, this paper systematically studies methods for impedance matching between dipole-type RFID tag antennas and tags ICs, which includes parasitical element loading, vee dipole technology and meander line loading technology. Not only geometrical parameters' influences on the impedance of RFID tag antennas are studied by experiments, but also causes and rules of those influences are explained theoretically or by empirical equations, which can be extended to design procedure with arbitrary RFID tag IC impedances.Third, fractal theory is one powerful tool to realize multi-frequency band and miniaturization for antennas. This paper applies the fractal theory to RFID tag antennas, in order to reduce antenna size. Fractal orders' influences on antennas' performances are studied, and the merit that RFID tag antennas in fractal structures own a good size-reducing feature is testified. Fractal structures studied in this paper includes Manderlbrot, fractal tree, Koch and Hilbert, etc.Fourth, this paper studies Minkowski fractal structure's influences on characteristics of microstrip antennas, designs and manufactures reader patch antenna and reader array antenna based on Minkowski fractal structure. It is testified that Minkowski fractal microstrip antenna is suitable to be applied to reader antenna and antenna array, which demonstrates good size-reducing feature meantime.