An Analytic Model for Impedance Calculation of an RFID Metal Tag

Since low-profile metal tags are infamous for their narrow bandwidth, obtaining fast and accurate impedance computation is therefore an important issue in the antenna design stage. This letter presents a method for computing antenna impedance of a patch-type radio frequency identification (RFID) tag. In order to perform impedance calculation in a very short time, an analytic model is proposed, and the result is highly agreeable with that obtained by the commercial software. Two important parameters are also identified for the purpose of independent impedance tuning of the real and imaginary parts. A prototype was designed and manufactured based on the proposed method, showing a dimension of 118 × 43 × 1.5 mm³ and a reading range of 6 m.