Compact Folded C-Shaped Antenna for Metal-Mountable UHF RFID Applications

A new type of C-shaped antenna, which is designed by combining a loop antenna and a planar inverted-L antenna, is proposed for designing a miniature tag antenna for on-metal applications. The proposed tag antenna can be easily made by folding a piece of flexible substrate. It is electrically small and low in profile, with a circuit size of 40 mm × 40 mm × 1.6 mm (0.122λ × 0.122λ × 0.005λ). The antenna consists of five patch segments, which can be adjusted for achieving multiple degrees of tuning freedom. By tuning the antenna impedance, a conjugate match can be easily obtained. When mounted on a 20 × 20 cm² metal plate, the proposed tag antenna is able to achieve a maximum read distance of 9.2 m with equivalent isotropic radiated power of 4 W, which is much better than the conventional loop antenna. The operating frequency of the proposed tag antenna is found to be very stable and it is not affected much when the dimensions of the backing metal object are varied.