Gain Enhancement of a Looped Slots Patch Antenna for Passive UHF RFID Tags Applications in Metallic Supports

The objects with high conductivity such as metals consist of a challenge for passive RFID (Radio Frequency IDentification) tags in UHF (Ultra High Frequency) due to their effects on tags antennas performance. In this paper, a passive antenna for UHF RFID tags applications on metallic supports is presented. The antenna structure is constituted of a rectangular patch with looped slots printed on three-layer substrate and deposited on a regular ground plane. The looped slots are used to match the antenna impedance to the chip impedance in order to maximize power transfer. The three-layer substrate is adopted to improve the antenna gain, and the regular ground plane is added to act as fixed-size metallic plate. The antenna performance in free space and the one attached to the metallic surfaces are compared. The metallic plate size variation effects on antenna performance are studied by fixing the proposed antenna over different sizes of square copper plates which are multiple to the antenna size, and evaluated using the 3D electromagnetic simulator: HFSS (High Frequency Structure Simulator). The proposed antenna is designed to be used on high dimensions metallic objects such as the containers. It achieves a stable performance when the metallic surface size is five times larger than the antenna size: a read range of 16 m, an antenna gain about 2.5 dB and a bandwidth that covers all passive UHF-RFID band.