High Gain Antenna Design For UHF RFID Applications

As a non-contact identification technology, RFID(Radio Frequency Identification) technology has been applied to various fields of logistics, retail, industrial and so on. A RFID system includes readers,tags and application software, mainly used in LF, HF, UHF and microwave bands. With the market needing the better performance used in RFID system,in order to promote the development and the popularization of RFID technology, hardware and software need to be further optimized, in particular, it is needed to solve the problem of identification range and accuracy rate of RFID systems.By studying the antenna theory knowledge, mainly focusing on research and analysis of the design principles of circularly polarized antennas, wide beam antennas and high gain antennas, combining present application situation and domestic and foreign research results of RFID reader antenna, a wide-beam circularly polarized reader microstrip antenna is designed to expand the recognition range of reader antenna used in the radio frequency identification system. Circularly polarized wave is excited by orthogonal feeding using wilkinson power divider with phase difference of 90 degrees. The antenna design includes the technology of coupling feed using circular metal sheets, slotting on patch and the use of a folded conducting wall. The overall dimension of the antenna is 113mm×113 mm×13.27 mm. Bandwidth of circularly polarized axial ratio and impedance covers 840 MHz-960 MHz. 3 dB beam width of the antenna is 104 degrees, and the gain is 4.8 dBi.In order to improve the gain and the identification range of reader antennas in actual application of the warehouse and inventory management,a RFID beam scanning array antenna for UHF band is designed, used in RFID system to identify many tags efficiently. High-gain circularly polarized antenna elements is designed using air layer structure and a planarantenna array is designed. Feed network is made up of Wilkinson power dividers and switched-line phase shifters, and the FPGA programmable module changes the phase values of antenna elements regularly.Performance Testing of the sample uses the microwave anechoic chamber,RF network analyzer, and the RFID reader. Test results show that the beam deflexion in four directions is realized and many tags can be identified quickly.