RFID tags, RFID readers and even RFID reader antennas sometimes give read range as a feature in their datasheets. Learn how to correctly interprete this value or which questions to ask.
Read range is one of the key characteristics of UHF RFID systems. Even though the read range is a specification of the complete system – it is so even for a specific set up, not for the system itself – this is such an important parameter for customers that both tags and readers give it as a specification of the component itself. Download our free eBook ‘The secrets of read range in UHF RFID sensor systems‘ now.
UHF RFID readers
UHF RFID readers often times give a value for read range capabilities. This value is very vague, unless the manufacturer shares more data about the set up to achieve that read range. For example, given the same physical set up and same RFID tag, reader A may be sharing a 6 meter read range using in their tests a 6 dBi antenna while reader B may be sharing those same 6 meters using a 3dBi antenna.
Notice that reader B is capable of reading the same RFID tag in the same set up with an antenna that has half the gain than reader A needs.
The correct specification for read range in a reader should be output power and not read range. The higher the output power, the longer the read range.
UHF reader antennas
UHF reader antennas are key in RFID systems even though most of the times you will not hear much about them. Antenna gain is a key factor in the read range of an RFID system. The higher the antenna gain, the longer the read range.
You will find the antenna gain given in two different units: dBi and dBm. For antennas, the most common reference unit is the dBi, which states the gain of an antenna as referenced to an isotropic source. An isotropic radiator is a theoretical ideal transmitter that produces useful electromagnetic field output in all directions with equal intensity, and at 100% efficiency, in three-dimensional space. Since it is theoretical, it is always the same, making it very easy to compare antennas.
dBm refers simply to the fact that the reference is 1 milliwatt (1 mW) and therefore a dBm measurement is a measurement of absolute power.
UHF RFID tags
UHF RFID tags are the third key component of the RFID system. These include both the RFID IC and the tag antenna. For simplicity’s sake we will take the RFID tag as a single component.
As with readers, you will also see read range as a specification in tag datasheets. However, this time manufacturers generally tend to indicate the details of the set up – you will see they use 2W ERP or 4W EIRP power sources, as these are the highest output power levels allowed in Europe and the USA respectively.
You may also find some tags giving you their sensitivity and antenna gain. Sensitivity is the lowest power required by the RFID chip to work while the antenna gain is exactly the same as the gain in the reader antenna – generally a lower value due to tag antennas being smaller in tags.
As you can see, read range is not a specification of any component in the RFID system but a specification of the complete RFID solution.