Radiation pattern of both reader and tag antennas have a great impact on the read range of RFID systems. Understand the basic implications.
Once again, the title is not completely true but helps understanding and choosing the right antennas for your application.
The truth is radiation pattern of an antenna does not hold a direct relationship with read range. The radiation pattern tells you how the RF field will be generated/propagated if you use that specific antenna.
Isotropic vs. highly directional antennas
For example, isotropic antennas generate an RF field that propagates all around the antenna. No matter where you physically locate – right, left, up, down, front or back of the antenna – you will be under the effect of the RF field.
On the contrary, highly directional antennas concentrate the RF field in a specific direction so you will have to take that into account for your RFID system set up.
With the information so far you would hardly ever go for a highly directional antenna as it limits the performance of the system. Here is where the title starts making sense: highly directional antennas, due to concentration of the beam width, tend to provide longer read ranges.
In general, antenna gain of highly directional antennas is higher than that of isotropic antennas. Think about the reader side: if the reader generates up to 30 dBm at the antenna connector, an isotropic antenna will spread the power in all directions.
However, a directional antenna uses the same 30 dBm but directed to a single direction. This results in the length of the radiation pattern reaching further than that of the isotropic antenna for the same amount of energy.
How do I select between isotropic and directional antennas?
Selecting the proper antenna requires a good understanding of both your RFID system and the application you are targeting.
An RFID gate solution for item tracking in supply chain for example uses multiple reader antennas in a single gate. All of them are directional antennas in general, providing a good coverage inside the gate area but very poor performance out of the gate. RFID tags will only be detected when going through the gate, but hardly ever before or after that – which makes sense for the application.
When talking about RFID sensor solutions, that is quite a lot trickier. Many times the setup is not static, meaning either the reader or the tags are moving in relatively random ways. On top of this, if read range is not a key factor, isotropic antennas may be the best fit for your application.
For more information about read range in RFID systems download the ‘The secrets of read range in UHF RFID sensor systems‘ free eBook.