An I-C Shaped Via-Patch Antenna with High Directivity and Wideband for RFID Tag Mounted on Metallic Surface

Abstract

This paper describes a miniature UHF RFID tag which provided various techniques to tune the input impedance and improve the directivity pattern of the proposed electrically small antenna on metallic objects. The low-profile tag antenna is formed by the two I-and C-shaped radiating plates and a cutted ground plane. The cutted ground plane was connected to the radiating planes through the four shorting vias and excited by a feed in the gap of the bottom edges of the I- and C-shaped radiating plates. To achieve the complex conjugate input impedance of an RFID microchip, the proposed antenna was coarsely tuned by the open slot 1 and 3, and adjusted fine by the open slot 2. Besides, changing the length of a cut ground space significantly enhanced the directivity patterns and radiation efficiency. The optimized antenna prototype with compact dimensions of 28.02× 25 × 3.2 mm3 ( $0.086\lambda_{0}\times 0.076\lambda_{0}\times 0.0098 \lambda_{0}$ ) yields a reading distance of 7.4 m, a high directivity of 6.7 dB, a radiation efficiency of 22% and a wide bandwidth of 43 MHz, which covers the entire North America band (902 – 928 MHz).