Shorted Patch Antenna with Tuning Slit for RFID Tag Mounted on Metallic Plane

This study developed a novel shorted antenna with tuning slit for radio frequency identification (RFID) that mounted on a metallic plane. Conjugate matching of the resistance and inductive reactance of the antenna to the desired chip impedance can be performed by simply tuning the length of the slit etched on the patch. An Alien Higgs-4 chip (8.1-j149 Ω at 925 MHz) was connected to the short side strip of the feeding loop. The gap of 0.1 mm between the proposed antenna and the metallic plane can enhance the antenna gain from the reflection of the plane. After analysis and optimization of the tag antenna, fabricated tags mounted on a metallic plane had impedance bandwidths of 2.2%. In tests of an RFID reader with an effective isotropic radiated power (EIRP) of 4.0 W, the maximum read ranges for tag in an outdoor environment was 8.1 m.