A novel antenna design for UHF RFID tag on metallic objects

A novel microstrip patch RFID tag antenna with wideband characteristic is proposed. It has less sensitive characteristic against size of metallic object, wide impedance bandwidth and long reading distance. The antenna consists of shorting strip, open stubs, tag IC and radiating patch having I-shaped slits. The proposed antenna is located on the finite ground plane and is constructed on FR4 substrate (epsilon(r) = 4.4,tan delta = 0.02). Overall dimension of the antenna is 100 mm x 26 mm x 6 mm. The tag IC has input impedance of 43 - j800 Omega at 915 MHz. The -3 dB impedance bandwidth is from 696 MHz to 978 MHz. When the antenna is placed in free space and mounted on 200mmx200mm, 400mmx400mm and 600mmx600mm metallic plates, the peak gains are 4.7dBi, 2.4dBi, 2.3dBi and 1.7dBi, respectively. The radiation efficiencies are 69%, 40%, 38% and 38%, respectively, and the maximum reading distances are 5.13 m, 6 m, 5.75 m and 4.75 m, respectively.