RFID antennas – which one to choose?
The antenna is selected based on several parameters. We distinguish between smaller and larger antennas, polarized omnidirectionally and directionally, left or right torsion.
The RFID antenna draws power from the RFID reader. Then it sends it in the form of a radio wave to an RFID tag within its range. If the readers are the brains of the RFID system, then the antennas are its arms. Because they transmit and receive information between the RFID tag and the reader. RFID antennas usually look similar physically. What distinguishes them from each other is the technical specification. When choosing an antenna, you should take into account several parameters that you will find in the product data sheet.
Frequency range
In each country, there are relevant regulations defining the ranges of acceptable UHF RFID transmission frequencies. The three most common frequency ranges for UHF RFID antennas are:
- 865-868 MHz (EU / ETSI,
- 902-928MHz (US/FCC),
- 860-960 MHz (global).
When selecting an RFID antenna, be sure to select a frequency range that is appropriate for the region where it will operate.
Reinforcement and opening angle
Gain and opening angle, also known as beamwidth or beamwidth, are strongly related to each other. The greater the gain, the narrower the radio wave, which equals a narrower coverage area, but the beam reaches a greater distance. To sum up, the amplification affects the width of our wave. The higher the gain, the more our wave is focused. It is easiest to imagine using a stronger and a weaker flashlight beam where the analogy is similar. The selection of the ideal antenna depends on the solution. If we have many tags in a short distance, it will probably be better to choose an antenna with low gain and a larger beam width.
Polarization
Another factor that improves its selectivity is polarization. Omnidirectional antennas read tags regardless of their position in front of the antenna. If we use a polarized antenna, e.g. horizontally – the RFID tag placed horizontally opposite will be read at a greater distance. If we rotate the tag by 90 degrees and its antennas are inconsistent with the polarization of the antenna, their reading range will decrease significantly.
If in the identification process we have to distinguish tags that are close to each other, e.g. on the production line, they should be directed vertically (the antenna is set in the same vertical polarization). In this configuration, even if the tags are close to each other, they can be read individually. In this variant, we should use smaller antennas with lower gain. Polarized antennas have another advantage, due to their directionality, they can read tags from an even greater distance than with omnidirectional polarization.
Such functionality is desirable, for example, when it is necessary to find a specific product with a specific tag in the warehouse. Directionally polarized antennas (horizontally or vertically) are also used when registering competitors running in sports competitions.
Circular Polarization vs. Linear Polarization: Which Antenna is the right one?
The choice between circular polarizing antennas and linear polarizing antennas can make a significant difference to your RFID solution.
Linear polarization occurs when electromagnetic waves are emitted in one plane (vertical or horizontal). Linear polarization antennas are best used when all RFID tags are placed in the same orientation and at the same height. Due to the concentrated emission, linear antennas typically have a longer reading range than omnidirectional antennas with the same gain.
Omnidirectional antennas are better in solutions where we are unable to predict the location and orientation of the RFID tag. They emit waves resembling the movement of a corkscrew in two planes. Because omnidirectional antennas lose their power on two planes, their reading range is shorter compared to linear antennas.
When deciding what type of antenna to use in an RFID system, it is critical to understand how these antennas work and how the RFID tags are oriented in relation to the antennas.
RFID antennas - types
Small and large RFID antennas
The basic criterion for the selection of the antenna is its size, the larger the antenna, the greater its range and it will be possible to read RFID tags from a greater distance. Antennas are therefore selected for the area to be covered. If the area is large, we give a larger antenna or several smaller ones. If we need to identify tags more selectively, we use a smaller antenna.
Internal and external RFID antennas
Another factor is the application of the antenna to the specific environment. They are usually divided into indoor and outdoor antennas.
Outoor antennas are usually more resistant to external factors, i.e. dust and moisture. All electronic devices have a degree of protection against the ingress of dust and water according to the American standard IEC 60529 and the British standard EN 60529 in the range from IP 00 to IP 69.
The main difference between external antennas and internal antennas is a greater range of temperatures in which they can operate, and resistance to condensation. For example, if you have a loading dock and you want to install antennas inside the gate opening, condensation will occur when the gate is opened for the time of loading, which will result in faster wear of the antennas and cable connectors.
If you install the wrong antenna for the environment, you can expect unstable operation of the RFID system, which may become completely unresponsive over time.
External antennas and antennas with built-in RFID reader
The antennas can be integrated in one housing with the RFID reader and purchased as one device, or work separately.
Devices with a built-in antenna allow you to save space and build a more mobile system without worrying about cabling. This solution may be optimal for retail solutions as it is usually small, easy to use and more visually appealing than two bulky external devices.
Readers with a built-in RFID antenna are also mobile terminals because there is a reader and antenna in one device. Often in difficult working environments, e.g. in paint shops, readers with an RFID antenna are used in one device.
On the other hand, external antennas provide much more configuration options and flexibility for different applications.
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