Electrically small antenna design for RFID Tag applications

The design of an Antenna for RFID tag applications with enhanced bandwidth and gain suitable for metallic environment applications with long read range, achieved by the use of large sized ground plane is proposed in this paper. Whenever the RFID antenna is used in the metallic environment, gain is degraded because the metal keeps on detuning the RF signal. In order to overcome this problem the bandwidth has to be increased such that the operational frequency does not shift rapidly over 3 dB variations. But there is a tradeoff between bandwidth and gain. In this paper two different substrates with high and low Permittivity is combined to achieve both gain and bandwidth, thereby overcoming the tradeoff uncertainty, i.e., substrate with high permittivity provides good radiation properties with high gain. On the other hand low permittivity substrate provides large spectral width. By combining these it acts as a push pull action, thus it compensates each other for the enhancement of output parameters. The current flow in the antenna directly contributes to the gain parameter. As the miniaturization of the antenna increases the rejection of current cancellation becomes a more difficult task. To eliminate the current cancellation in a miniaturized structure the large ground plane structure of about four times greater than the antenna area is considered, which eliminates the spurious radiation cancellation. The read range and quality factor can be increased by shortening the dipole antenna at its quarter wavelength.