Research Of Microstripantenna For RFID Reader

Microstrip antenna is an important member of the antenna family,it has been widely used in mobile communication,satellite communication and other fields.Especially in recent years,with the rise of RFID technology,circularly polarized,broadband and multi-frequency working characteristics of reader and the tag antenna has became the main research trends.In this paper,we did a research on the microstrip antenna about its miniaturization and multi-band,meanwhile,we also studied the multi-feed technology on circular polarization.Based on the cavity model theory,studied the influence of microstrip on miniaturization,multi-frequency working and expanding bandwidth by using short circuit loading and coupling resonance technologies.In the circular polarization microstrip antenna method,studied the effect of sequential rotary multi-point feed technique on the bandwidth of circularly polarized axial ratio.And as a basis,designed two microstrip antennas for RFID systems.First designed a dual-frequency microstrip antenna working in 2.45 GHz and 5.8 GHz band of RFID,the size is small,and can be applied in handheld RFID readers.Physical antenna was fabricated and tested,its impedance bandwidth in the low frequency band is2.40-2.47 GHz,and the actual gain is greater than 2 dBi.The impedance bandwidth of high frequency band is 5.67 to 6.25 GHz,and the actual gain greater than 4 dBi.Two purposes for using short-circuit loading technique,one is that made the antenna working at a quarter wavelength in the low frequency band,thereby realizing the miniaturization of the microstrip antenna;The other is to broaden the impedance bandwidth of the antenna in the high frequency band.Then,designed another circular polarization antenna working in 2.45 GHz,it is mainly used in 2.45 GHz active RFID indoor positioning technology.Due to the use of wide-band feed network,it has a wide impedance bandwidth of 2.3-2.7GHz.By using four feed points and delaying the phase by a successive quarter wavelength,it has a lower axial ratio,and its 3dB axial ratio bandwidth covers the 2.45 GHz frequency band of RFID technology.In this frequency band,its gains are all above 7 dBi,and meeting the needs of2.45 GHz active RFID indoor positioning.