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.