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TRF7960 antenna size for 1 meter read range

Greg Dettro
Prodigy 80 points
Other Parts Discussed in Thread: TRF7960

Hi,

Design will use the TRF7960 Hi Frequency RFID reader.  Requirement is to be able to (fairly) consistently read a tag at a distance of 1 meter (basically 40 inches).  Appliction Report SLOA135, Antenna Matching for the TRF7960 RFID Reader, states that "A rule of thumb is that the expected read range is twice the antenna diagonal measurement".  Does this imply that the inner diaganol of the antenna needs to be on the order fo 20 inches for a read range of 40 inches?  Can the TFR7960 drive an antenna of this size?  If not, what would the recommend circuit be for implementing a hi frequency RFID Reader to read tags at a distance of 40 inches? 

Thanks,

    Greg

  • 0
    TI__Guru* 91216 points

    Greg -

    if it were only that easy...to but some perspective on this...the comment in the app note is aimed at smaller antennas and in practice - the true "rule of thumb" read distance with ID1 size tag ISO15693 (45mm x 76mm) is closer to the diagonal of the coil (if it is a square or rectangle) or the diameter (if a circle) multiplied by a golden ratio # like 1.618. Could be that someone rounded up here...

    At any rate - the TRF7960 @ 200mW driving a larger antenna (like for example a 30cm or 48cm square antenna) yields read ranges (with ID1 size tag) of about 28cm and 46cm,respectively, so you can see that the "rule" falls apart. This is due to the fact that while the magnetic field is larger, it is also weaker, so this is a limitation for trying to read out from longer distances.

    So, as you mention - an amplifier could be used, but i would say a larger antenna should also be used. A reader antenna on the order of 60cm x 80cm and several watts of output would more than likely suffice to read these distances - but this is not a trivial engagement. I would recommend folks use Feig Electronics HF readers and antennas for longer range operations. They make very reliable devices and have significant TI content inside...the LR2000 is good starting point here to have a look at. http://www.feig.de/index.php?option=com_content&task=category&sectionid=12&id=52&Itemid=127  and antennas are here ==> http://www.feig.de/index.php?option=com_content&task=category&sectionid=12&id=54&Itemid=130