An RFID antenna consists of a coil with one or more windings and a matching network. It radiates the electromagnetic waves generated by the reader, and receives the RF signals from the transponder.
An RFID system can be designed so that the electromagnetic field is constantly generated, or activated by a sensor.
Antennas also come in different sizes and designs, this depending very much on the environment into which a system is integrated. The required read and write range also play a role.
Common forms are rod or loop antennas. For greater reading range or different orientations of a transponder, a number of antennas can be arranged in one reader unit.
In this technology, the antennas are different with regard to configuration and mode of function depending on the frequency used.
LF (Low Frequency) – 125 / 134.2 kHz
The antenna is comprised here of a defined number of wire winds which thereby result in a defined inductance in the antenna. A difference is made here between frame antennas (air coils) and rod antennas (coil with ferrite core). Within the complete system, the magnetic near field is used, i.e. inductive coupling.
HF (High Frequency) – 13.56 MHz
Within the HF range, the antenna is comprised of one or more windings and is frequency tuned by a connected tuning board. The antenna winding material should have a large area when possible because in the HF range the waves spread out on the surface of the condustor and more current can flow through a larger area, thereby influencing the performance of the antenna. Within the complete system, the magnetic near field is used, i.e. inductive coupling.
UHF (Ultra High Frequency) – 865 to 950 MHz
Here a distrinction is made between two types of antenna – dipole and patch antenna. As already suggested by its name, the dipole antenna is a design that comprises two poles. The chip is arranged in the middle and the two antenna poles are to the side. The patch antenna is a metal surface which must have defined edge lengths. The surface thereby functions as a resonator. Within the complete system, the magnetic distant field is used in these antennas, i.e. electromagnetic coupling.