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Omnidirectional RFID UHF antennas with medium (~25mm) range recommendations?

penguin

Please bear with me as I couldn't even be considered a novice yet. I'm just a coder with an idea that I want to try out using RFID technology.


I want to identify and record data from passive RFID tags that are up to approximately 10 inches (25 cm) away from the device in any direction. There may be a few inches of low density foam between the antenna and the RFID tags. Small size and weight are important factors. Number of simultaneous tag reads... let's say, up to 5 at a time.

Based on my online research, I've come to the conclusion that a UHF reader is the way to go however, it seems like all antennas are either very short (few inches) or very long range. Can anyone recommend some antennas that might be suitable for these requirements?

Thanks in advance.

  • 0

    I have done passive RFID at 134 KHz at 10 inches using a coil about 8 inches in diameter - if that helps.

    The RFID tags are small of course, but scavenge enough power from the reader signal to send back data.

  • 0

    That's quite normal, because a lot of antennas need some distance (far-field) to perform well. Whereas, in the range you're looking at (near-field), you're likely at the extremity of signal strength at 10 inches at UHF for near-field antennas. Compounding that, is that you're looking for a very wide radiation pattern which means signal strength will not be concentrated.

    I'm no expert, but I suspect you might need a far-field antenna positioned at a greater distance (I don't know your application). The far-field antenna at a distance will get you the coverage you desire without the need for a closer (near-field) antenna with omnidirectionalty I think. It's probably worth talking to either an antenna manufacturer or the RFID reader manufacturer (who will be quite experienced because they know what their customers use).

    Also, tag antenna shape/size will make a big difference, so you might want to experiment with several (assuming that's something you are able to modify in the solution).

  • 0

    The PN5180 readers use ISO15693 standard and get about 15cm without increased antenna size.

  • 0

    Thanks for your suggestions, much appreciated. A lot of it is way over my head... I'll need to take some time to learn what it all means. I did chat with atlasrfid store and they said that WANT020IP and WANT021IP antennas could be good options. A quick search suggests those aren't widely available and one site was $150/each with a 10 minimum order. lol 
    So, I may first try some of your (shorter range) ideas mentioned here first, then scale up if/as needed.

  • 0 in reply to penguin

     AND... welcome to element14.  There is so much here that is over my head as well.  There are quite a number of super smart people here that are willing to help - as long as you are genuine.  It's what I love about the community.    and  are some of the best.  You are wise to take their guidance. Thumbsup

  • 0

    You didn't mention what region you require operation in, but if it's Europe, then this antenna looks ideal and is low-cost:

    https://www.digikey.co.uk/en/products/detail/kyocera-avx/9000468/21442857 

    It is omni-directional, and I suspect (can't guarantee it, you'd need to try it) that it may support the range you're looking at.

    However, you'd need to mount it to a 70 x 70 mm ground plane, which is pretty easy to DIY (you can get the PCB ground plane manufactured for sub-$10, even in single quantity, from many PCB manufacturers in China).

    If you're in North America, then this antenna looks suitable:

    https://www.digikey.co.uk/en/products/detail/kyocera-avx/9000469/21442939

    Again, it requires the 70 x 70 mm ground plane. If you need more info about how to make the ground plane, let me know.

    (And again, no guarantee it will support the range you're looking for, but at the low price it's definitely worth a shot.

    The ground plane will end up looking something like this (the example here is for GPS, not RFID, but it will be almost identical).

    image

  • 0 in reply to shabaz

    I ended up creating a PCB that will accept those antennas (or GPS antennas, and some other patch antennas too):

    image

    All it needs (other than the patch antenna) is a 0-ohm resistor (0805 or 0603 sized) and a U.FL socket (an example is Molex 73412-0110).

    There's space on the board for matching components if it comes to that, but it should be unnecessary.

    image

    The board fits some Hammond plastic enclosures (ideally, glue the board on the edges inside, to avoid using metal screws).

    Also an RF cable is needed (U.FL on one end, and whatever desired connector on the other).

    In case anyone wants such a generic patch antenna board, the zipped PCB files are here (ready for directly uploading to any PCB manufacturer). It costs £30 GBP to order 15 of these boards, with ENIG finish, including shipping. 

  • 0 in reply to shabaz

    Board with the 868 MHz ceramic patch antenna attached.

    image

    The underside has the U.FL connector, and should have a 0-ohm resistor, but I've not soldered that in yet (because I want to measure the impedance first).

    image

    I used a U.FL to SMA socket cable (pre-assembled). 

    For 3D-printing an enclosure, the main dimensions are the same as Hammond 1551XBK, but the depth will need to be tailored to suit whatever connector is used, if it is a panel-mount item.

  • 0 in reply to shabaz

    Measurements!

    The results are not significantly different from the datasheet, for almost 2/3 of the frequency span. I wouldn't expect it to be identical anyway since there's no guarantee I tested in the same environment or the same orientation. I happened to test with the antenna facing vertically upwards.

    This was my first time using the NanoVNA (there are different models, I have the -H4 model) to measure an antenna. Impressive how good it is. Now I understand why people rave about NanoVNAs, it's justified.

    image