Analysis And Design Of Microstrip Antenna For Passive RFID Tag

Radio Frequency Identification (RFID) has been one of the most popular automatically intelligent identification technology in the recent years, which can identify the target and exchange useful digital information via non-contact radio frequency communication, between RFID readers and RFID tags. Compared with other identification technology, RFID has higher precision, faster identification speed and stronger ability to adapt the unconstant environments. As a sub-system to RFID, the RFID tag has many limitations on its physical size, due to the actual application situation. Considering the problem above, designing the antenna for RFID tag has its own specialties and difficulty, in the most cases, micro-strip antennas, which have many good characteristic of small volume, light weight, thin section plane, easily manufacturing and matching well with other electronic units, is adopted into the RFID tag antenna's designing. However, the traditional micro-strip antenna has its inborn drawbacks, such as narrow bandwidth, high power loss, small radiation power, etc, which are the obstructions preventing the application of micro-strip antenna in the RFID field. So it is very urgent to perfect the micro-strip antenna, which is also valuable for the popularization of RFID technology.This article introduces basic knowledge concerning RFID technology and explains the working principle of the RFID at the beginning. Then, the performance parameters related to the designing antenna are researched and discussed. The main task done by this article is to make a research on impedance-match and coaxial probe fed , propose a novel design of circle polarized patch Antenna with complex substrate for passive RFID Card, which aims at resonating at 2.45GHz. Ansoft HFSS 9.0 is employed for simulation and optimization, simulation results match the theory-expectation, through optimization, the system performance meets the requirements needed, such as good directivity, bandwidth>50MHz (S₁₁<-14dB) , main beamwidth>70 degrees, gain 5.534dB, standingwave ratio, radiation efficiency. Compared with the traditional design, the new one is easily realized, and more reliable. Further more, the effect of external environment on the antenna is discussed at the end of this paper.