Contents I. Introduction
RFID systems are widely used for identification and tracking of objects. The system consists of an active reader that illuminates the room and reads information from a passive tag antenna. Most systems in the UHF band make use of planar antennas with good radiation characteristics to achieve electromagnetic coupling between the tag and the reader. Thin form factor, placement-insensitivity, small size and good radiation characteristics are essential qualities of planar RFID tag antennas operating in the UHF frequency band. In several applications, RFID tag antennas are mounted on top of con-ductive objects which can lead to a degradation the radiation characteristics of the tag antenna. It has been shown that placement-insensitivity can be achieved by incorporating a conducting back plane [1]. However, when a planar antenna is placed in close proximity of a conducting back plane, the performance of the antenna degrades considerably. The bandwidth of the conductor-backed antenna is reduced due to increased coupling between the currents in the antenna and the image currents in the back plane. The radiation efficiency of the antenna is also reduced. Edge treatment in the form of serrations has been shown to improve the bandwidth and radiation efficiency in planar antennas [1]–[5]. The radiating behavior of edge-treated planar antennas has been studied using transmission line models [1], using fullwave numerical analysis [2]–[5] and statistical methods [6]. While transmission line models help understand the behavior of serrations for lower frequencies, they cannot accurately capture the behavior of the serrations at higher frequencies. Although fullwave numerical techniques help understand the general behavior of edge-treated planar antennas, the analyses is often presented for planar antennas with a particular serration geometry and with the feed mechanism included in the analysis. In such cases, the total current distribution on the antenna is due to the serration geometry, the chosen feed-type and the chosen feed-location. Thus, the radiation characteristics become a function of the serration geometry and the feeding mechanism. There is a need for dissociating the effects of the serration geometry from that of the feeding mechanism in order to understand the effect of the serrations on the radiating characteristics.
