An LC balun integrated microstrip TWA for precise near-field localization system in UHF RFID

An LC balun integrated traveling wave antenna (TWA) for precise near-field localization systems is proposed. The proposed antenna fed by a grounded coplanar waveguide (CPW) line consists of a LC balun, 50Ω loads, and differential-fed microstrip lines for uniform H-field distribution. To reduce a standing wave in the microstrip lines, 50Ω resistors at both ends of the differential microstrip lines are inserted as loads. By differential currents along two microstrip lines, the uniform magnetic field at the area between two lines is generated. The proposed compact TWA operates at the authorized universal UHF RFID band, and the measured impedance bandwidth based on the −15dB reflection coefficient is 0.84–0.95 GHz. The proposed compact TWA can be used for smart drawers or smart shelves which need precise localization.