An accurate method for impedance measurement of RFID tag antenna

Abstract

This paper presents a method of antenna impedance measurement for RFID tag antenna based on a, differential probe. The importance of accurate impedance measurement in optimal design of tag antenna, especially for the metal tags, is first addressed. Afterwards, an overview of the existing methods based on the single-ended probe and the balun probe is presented. The proposed method using the differential probe is explained based the well-known two port network model. Experiments for both balanced and unbalanced tag antenna measurement demonstrate the differential probe can provided better agreement with simulated results.