An Internal Coupled-Feed UHF RFID Tag Antenna with CP and Metal-Mountable Advantage

Abstract

An internal coupled-feed microstrip RFID tag antenna for UHF band is presented in this article. To achieve a compact size, the orthogonal cross-slot is etched on the radiation patch, reducing antenna size and providing feeding space for L-shaped feedline. In order to meet the metal-mountable advantage and the low-profile size requirement, the ends of L-shaped feedline are connected with ground through metal-via. By optimizing the size of L-shaped feedline, the expected input impedance of the proposed tag antenna can be obtained easily. Moreover, the target band of circular polarization (CP) can be covered by optimizing the length of slits, which is embedded in the four corners of the radiation patch. The measured 3-dB Power Reflection Coefficient (PRC) bandwidth of the proposed tag antenna is 98 MHz (from 840 to 938 MHz), and its 3-dB axial-ratio (AR) bandwidth is 7 MHz (from 920 to 927 MHz). Further test results demonstrate that the tag antenna can provide better gain and reading range when mounted on a metal plate.