Compact Microstrip RFID Tag Antenna Mountable on Metallic Objects

This paper presents a compact microstrip antenna that can be attached to a metallic object to form a passive radio frequency identification (RFID) tag operating in the UHF band. The proposed antenna was etched on an FR4 substrate with an overall size of 60 mm × 45 mm × 1.6 mm, and it consists of a matching network, two radiating patches, and a ground plane. Each patch was extended using a meandered strip and was shorted to the ground plane via four metalized via holes to form a planar inverted-F antenna (PIFA). When mounted on a 50 × 50 cm2 copper plate, the proposed antenna provided a 10-dB impedance bandwidth of 37 MHz (901∼938 MHz) and a power transmission coefficient (PTC) of 0.86 at a frequency of 915 MHz. Moreover, the maximum reading range of the prototype metallic RFID tag, measured using an UHF RFID reader system, reached about 6.2 m at 4-W EIRP radiation power.