A Compact UHF-RFID Tag Antenna With Embedded AMC for Metallic Objects

In this letter, a UHF-RFID tag antenna with a size of 40 x 40 x 3.2 mm(3) is proposed for metallic objects. It is composed of a modified folded dipolar antenna (MFDA) and an embedded 2 x 2 artificial magnetic conductor (AMC) array with shorting vias. Multiple slots are etched on the MFDA and AMC to increase the current path, where the slots on the MFDA is vertical to that on the AMC so that the currents on the MFDA and AMC do not affect each other. Thus, the slots can be adjusted independently without affecting the resonant feature of the MFDA. Equivalent circuit models are also presented to understand the impedance characteristics. A prototype mounted on a 20 x 20 cm(2) metal plate has been manufactured and measured. It is demonstrated that the proposed tag antenna shows a 3.9 dB gain enhancement comparing with the MFDA without AMC and a maximum gain of -1 dBi at 919 MHz. Moreover, a maximum reading distance of about 14.2 m can be obtained.