Phased Array Antenna Design For UHF RFID Readers

Radio frequency identification(RFID)technology has received increasing research effort due to its various applications such as logistics,vehicles identification,automatic charge and industrial production,etc.However,the large-scale application of RFID technology is limited by the short identification distance of the readers,small recognition region,large antenna size and other technical imperfections.As an important part of the reader,antennas play a crucial role in determining the identification distance,the recognition region and the volume of the reader.In order to reach a long identification distance and a wide working range under the limited power output of RFID reader,a novel design scheme of antenna is presented in this paper,which utilizes phased array antenna to achieve the beam scanning.With array antennas,we can make increase the gain by narrowing the main beam.Changing the excitation phase of antenna element,the main beam can be pointed to different directions.Therefore,a phased array antenna is not only advantageous by a high gain thus a long identification distance,but also a wide reader recognition region.Miniaturized element reduces the overall size of array antenna.An UHF band 1 ×4 microstrip phased array antenna is designed in this paper.The proposed antenna array has four microstrip patch antennas,operating at the frequency of 915MHz.The antenna element has the attractive features of low profile and light weight.Cutting narrow slots in the radiation patch and the ground plane,around 51%reduction of area is obtained compared to the slotless one.Chebyshev array antenna can achieve the desired characteristics for the primary and secondary lobes of the reader,in the sense that the primary lobe can be the narrowest for a specified level of secondary lobe,or the secondary lobe can be lowest for a specified width of the primary lobe.The antenna elements are spaced by ?/2.Excitation current amplitude meets the Chebyshev function distribution and the ratio is 1:(?):(?):1-The half-power point of the beams as the beam switching angle.The validity and feasibility of the proposed antenna have been simulated and analyzed by the High Frequency Structure Simulator(HFSS).The simulation results show that the array antenna has a gain of 13.73dBi and the main beam direction can be switched between the angles of ±55°,with a 3dB beam-width of 28°.In order to verify the proposed phased array antenna can improve reader performance,the feed network was design and the test platform was built.Experimental results show that compared with traditional single antenna,the proposed array antenna has a strong directivity and phased array antenna can expand recognition region of the reader and greatly improve the coverage area of the RFID system.