Small Wideband Antenna for On-Metal UHF RFID Tag Design

A double-layer antenna with a small footprint of 47 mm x 21 mm x 2.36 mm is proposed for broadband on-metal applications. Here, a rectangular loop is deployed to excite the underneath patch. A vertical slit is integrated into the patch to effectively improve the impedance matching between the antenna and the microchip as well as the tag bandwidth. The bandwidth tuning mechanism is simple and convenient. It can be easily done by adjusting the slit width or the slit position for different tuning sensitivities. Measurements have been conducted with the use of a 4W EIRP transmitting power, and the tag can be read from at least 4 m within a broad frequency range of 865 MHz - 960 MHz when it is mounted on different sizes of metallic plates (12 cm - 24 cm) and metallic items. The wide operating frequency range of the tag can cover both the European and U.S. RFID bands and it has a stable detectable range.