Bandwidth Improvement of Planar RFID Tag Antennas using Characteristic Mode Theory

Planar antennas have been widely used in UHF RFID systems. Placement insensitivity and thin form factor are essential qualities of planar RFID tag antennas. As the antennas become thinner, most of the energy is stored within the region between the antenna and the ground plane resulting in the degradation of bandwidth and radiation characteristics. Serrations can be used as edge treatment to improve the bandwidth of planar antennas. The analysis of edge-treated planar antennas using characteristic mode theory is presented in this article. The effect on serrations on the resonant frequencies and radiation characteristics of resonant characteristic modes of a rectangular plate is presented and guidelines are presented for improving the bandwidth of planar antennas.