Double U-slotted Antenna for RFID Tags Mountable on Metallic Surfaces using rectangular-loop feed

A double U-slotted antenna for radio frequency identification (RFID) tags mountable on metallic surfaces is presented. A novel rectangular-loop feed structure without any via-hole or shorting plate is proposed to perform inductive reactance. A pair of U-slots is presented to perform broad impedance band. The proposed design is verified by simulation and measurement. The measured maximum read range on a metal with a size of
$200\mathbf{mm}\times 200\mathbf{mm}$
is 1.4m
$(\mathbf{EIRP}=0.4\mathbf{W})$
. The measured impedance is proximately corresponding to the simulated results.