Modal-based approach to tune and enhance the frequency and dielectric bandwidth of a UHF-RFID tag antenna mounted on a dielectric substrate

A methodology to design an RFID tag antenna is presented. The tag is explicitly designed to account for changes in the dielectric constant of a thin substrate supporting the antenna. The theory of Characteristic Modes (CM), a modal-based approach, is used to study the effect of the dielectric variation on the dominant modes. The outcome of the CM analysis provides valuable guidelines to design a tag antenna that not only exhibits a large frequency bandwidth but also insensitivity to changes in the dielectric constant. Measurements and simulations show fairly good agreement. The proposed tag antenna is shown to have superior performance compared to commercially available antennas as well as antennas reported in the literature.

I. Introduction

Radio Frequency Identification (RFID) is a technology widely used in many applications including communications, sensing, medical, scientific, and others. One significant component of this technology is the RFID tag which is basically a chip that is attached to an antenna. The antenna is used to capture the RF signal coming from the reader and then re-send it, with the tag's pertinent information, back to the reader. In this type of antennas, it is extremely important to minimize the power loss due impedance mismatch between the antenna and the chip. This is especially important in passive tags where part of the received power is used to activate the chip. In addition, any mismatch will lower the read-range which is defined as the maximum distance at which the RFID reader can detect the back-radiated signal from the tag [1].