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I am trying to understand the RFID frequency bands but have some confusion. RFID tags operate on two different frequency bands 865 to 868 MHz (European) & 902-928 MHz. Are the RFID readers programmed to interrogate the tag at one single frequency e.g., 915 MHz or over the entire band ( 902-928 MHz?)

I have seen tag reading performance graphs over UHF range and the tag responds at all frequencies of course with varying read range. In this context does it make sense to compare the performance (read range) of different tags at a central frequency e.g. 865 MHz or 915 MHz?

If it's better to compare the read range of the tags over a range of frequencies (e.g. 902-928 MHz,) how would you conclude the best overall performance over the entire range? Can you simply average the read range at each frequency in the band?

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Passive RFID tags respond to a reader with power from the reader itself, and employ tuned circuits to match the impedance of the reader to that of the tag for optimum power transfer in both directions. It is theoretically possible to increase the range by narrowing the bandwidth for a more precise impedance match. However, in practice, RFID tags must respond over a range of frequencies as you have noted.

The actual range of frequencies varies in different countries, so reader (transmitter) frequencies must conform to the country in which they are operated. Some countries allow RFID operation in only certain portions of the two RFID frequency ranges you have mentioned. The tag should be chosen to operate in the full range of frequencies allowed in the country in which it is being operated.

In answer to your question, readers can "hop" between discrete frequencies inside of the band, changing from one frequency to another in a somewhat random pattern designed to prevent interference from other nearby readers, such that two readers have a low probability of operating at the same frequency for any extended period of time.

So, you should choose a tag with a read range curve that is fairly flat across the range of frequencies of which you intend to operate. Make sure you handle both ranges if your product has to operate in multiple countries. Remember that your range as shown in the data sheet is probably "best case," that is with the tag and reader optimally oriented and no metal or other materials nearby.

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  • \$\begingroup\$ Thanks for the explanation. So to quantify the read range over a range using a single number, could I just take the average of reading distance for the frequencies in that range? or would some statistic (e.g. using min max) be better able to represent & compare different tags? \$\endgroup\$
    – Zaffresky
    Dec 3, 2022 at 12:03
  • \$\begingroup\$ Safest oud be to use the minimum value over the frequency range in which you expect to operate, always keeping in mind that the antenna alignment has the biggest effect on range. \$\endgroup\$ Dec 4, 2022 at 18:30

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