Log-periodic dipole array with improved front-to-back ratio for universal UHF RFID handheld reader applications

This paper presents an antenna design for universal UHF RFID handheld readers. Four-element log-periodic dipole array was adopted as the basic antenna structure. The arms of the radiators were folded to make the antenna compact in size. Parasitic elements were also included to improve the front-to-back ratio. The fabricated prototype exhibited good impedance bandwidth covering the universal UHF RFID band from 840MHz to 960MHz. Besides, the overall radiation efficiency was above 80% across the entire band. A maximum of 10dB improvement in front-to-back ratio was achieved at 920MHz.