Radio Frequency Identification (RFID) is a tracking/identifying system used in many industries such as person or goods tracking, access management, payment collection and many other things. This technology is based on the high frequency data transfer from an electronic label (the “tag”) to a base (the “reader”) to process the data. The RFID tag should be reasonably small. It can be both active or passive. Regardless of the type, all RFID tags have two main components: an antenna which transmits and receives data and an integrated circuit (IC) called transponder that handles the data processing, data storing and signal modulating.
In this example, we have simulated an antenna designed for an RFID tag. This antenna has been reported in an IEEE publication in 2009 by LU et al.
Figure 1 - RFID Tag Antenna
Low-frequency (LF: 125 - 134.2 kHz and 140 - 148.5 kHz) and high-frequency (HF: 13.56 MHz) RFID tags can be used globally without a license. Ultra-high-frequency (UHF: 868 MHz-928 MHz) cannot be used globally as there is no common global standard.
Figure 2 - Frequency-ranges used for RFID-systems
As we can see on the figure, RFID tags can be used in multiple frequency ranges; The one that we adopted for this tutorial is around 2.45 GHz. Therefore, We create an antenna study, with a fast sweep frequency plan of 101 frequency distributed around 2.5 GHz and between 2 and 3 GHz. In a further step; we run a single point individual simulation at 2.45 GHz for radiation patterns plotting.
The antenna is built on a Duroid 6006 substrate and the printed layer is assigned a PEC boundary condition.
At the user-defined center-frequency, we can view the electric and magnetic field in different settings: i.e. iso and section clipping, animating the field through varying its omega-T phase, changing the colors of the chart to show relevant intensities. We find here a capture of an electric field distribution spotted within the surface of the antenna's board.
Figure 3 - 3D view of Electric Field distribution
Figure 3 - Radiation pattern of the antenna
For antenna's studies, it is always intuitive to fetch the best matching frequency at the input port. For this RFID tag antenna, we have return loss better than 20 dB at 2.45 GHz -which is ideal for the nature of the application-.
Figure 4 - Reflection coefficient at the antenna's port
Figure 5 - Return Loss of the filter within various configurations
The reflection coefficient can also be plotted on a Smith Chart and a marker is available for tracking the curve and discovering the convenient frequency for each point.
 RFIDEA: Engineering & Applications in electronic traceability