Research On RFID Reader Antenna Based On Magnetic Coupling In UHF Band

Radio frequency identification(RFID)systems for ultra-high frequency(UHF)operations based on magnetic field coupling have been rapidly developed in many applications such as logistics,pharmaceuticals management for its high-rate and good performance in complex environments.As internal part of RFID systems,reader antenna needs to generate strong and uniform distribution of magnetic field.Besides,a special antenna having multiple radiation properties separately for near-and far-field communication is useful.In this paper,research on RFID reader antenna based on strong and uniform magnetic field in near field is carried out.Furthermore,design of multiservice reader antenna working both in near-and far-field operations is also studied.A magnetic-coupling reader antenna with low far-field gain,a switchable antenna separately for near-and far-field operations,and a multiservice magnetic-coupling antenna are studied respectively.The main contents and research results are as follows:In Part ? of this thesis,a magnetic-coupling reader antenna with low far-field gain in UHF band is proposed,which is composed of straight dipoles fed by quarter wave impedance transformer double-side parallel stripline(QDSPSL)structure and can achieve strong and uniform magnetic field distribution.Measured results show that impedance bandwidth is 107 MHz(860-967 MHz).A reading region of 140×140 mm~2 and 100%reading rate within 100 mm for near-field tags are exhibited with an input power of 25 dBm.Moreover,a multiple-arm dipole antenna array is proposed to achieve stronger and more uniform field distribution based on the first structure,which also obtains broadband performance caused by different resonant frequencies.Simulated results indicate that impedance bandwidth is 810-1000 MHz and field strength is up to-2.5 dBA/m at the height of 10 mm from antenna surface.In Part ? of this thesis,a switchable antenna separately for near-and far-field operations in UHF band is proposed.Based on antenna prototype in part I,multiple-port antenna is designed to achieve different radiations.Far-field radiation for two orthogonal polarizations and near-field operation based on magnetic field coupling can be modified by feeding different corresponding port.Measured results show that impedance bandwidth is 820-880 MHz.A reading region of 140×140 mm~2 and 100%reading rate within 100 mm for near-field tags with an input power of 25 dBm are exhibited in near-field mode.In far-field mode,the impedance bandwidth is 820-1000 MHz and the antenna can achieve 1.2m read distance for far-field tags.In Part ? of this thesis,a multiservice antenna simultaneously for near-and far-field operations in UHF band is proposed.Based on the opposite directed currents(ODC)theory,the antenna achieves circular polarization(CP)radiation in far-field and simultaneously generates strong magnetic field in near-field region.Measured results exhibit a reading region of 100×100 mm~2 and 100%reading rate within 25 mm for near-field tags.In far-field mode,reflection coefficient is below-10 dB and gain is2.9-3.2 dB within 825-925 MHz.Axial ratio bandwidth(ARBW)is 30 MHz(880-910 MHz)and the antenna can achieve 1.6 m read distance for far-field tags with an input power of 25 dBm.