This paper addresses the performance evaluation of a modified square loop antenna design for UHF RFID applications that is excited through a narrow feed line connected to a square loop, an impedance matching network. The square loop dimensions are modified to reach a conjugate impedance matching. A gap is fixed between the feed-lines to link the chip. To achieve impedance matching, the structures of the feed-line are optimized accordingly. In addition, the antenna consists of a straightforward geometry. An 11.9-meter maximum read range is achieved using a compact size of 80 × 44 mm2 and 3.2 W for the effective isotropic radiated power. Additional findings reveal that the proposed tag antenna is able to provide a stable resonance response in the near field of a large metallic surface.
A semi-circle looped vertically omnidirectional radiation (VOR) patterned tag antenna for UHF (919-923 MHz for Malaysia) frequency is designed to overcome the impedance mismatch issue in this paper. Two impedance matching feeding strips are used in the antenna structure to tune the input impedance of the antenna. Two dipole shaped meandered lines are used to achieve a VOR pattern. The proposed antenna is designed for 23-j224 Ω chip impedance. The antenna is suitable for 'place and tag' application. A small size of 77.68×35.5 mm2 is achieved for a read range performance of 8.3 meters using Malaysia regulated maximum power transfer of 2.0 W effective radiated power (ERP).