I have a 902 MHz to 928 MHz UHF 8dBi far-field RFID antenna connected to a reader. I want to read RFID tags.

What will be the consequences if I used this UHF antenna in the near field range when it is meant to be used in the far-field range?

This is just an acquiring more knowledge sort of question. My intentions are to use this antenna in the far-field range but what will happen if I then place it in the near field range and scan RFID tags, will it still detect those tags in the near field?

  • \$\begingroup\$ Ah let me see. It is just like trying to use a long wave antenna to receive short wave radio signals, you cannot "tune" in signals not in your frequency band. \$\endgroup\$
    – tlfong01
    Aug 27 '20 at 2:45
  • 2
    \$\begingroup\$ @tlfong01 He is not talking about a different FREQUENCY but about different distances from the antenna. Here a poorly put explanation of sorts. Others may wish to put this better: At "long" distances from an antenna in the far-field the ration of E to M is stabilised to give the impedance of free space. At close distances in the "near" field the ratio of E & M vary. In the near field you can eg couple to the magnetic field of a resonant circuit (or a non resonant inductor) and transfer power which will not radiate without this coupling. In the far field power radiates regardless of coupling. \$\endgroup\$
    – Russell McMahon
    Aug 27 '20 at 6:36
  • 2
    \$\begingroup\$ @Joey I'd expect a far feild antenna to "function adequately" in the near field. I may be wrong :-). \$\endgroup\$
    – Russell McMahon
    Aug 27 '20 at 6:37
  • \$\begingroup\$ @Russell McMahon, (2) Many thanks for pointing out my misinterpretation of the OP's question and my ignorance about near and far field. I only know my mobile phone can do NFC and I have a RFID reader which I think can only read RFID tags near field. So I googled and read the following article to learn more. I found the article a bit hard to read, because there are quite a lot things I don't know that I don't know. (1) Understanding Near-Field and Far-Field Antennas - Suzanne Smiley 2014nov12, atlasrfidstore.com/rfid-insider/… \$\endgroup\$
    – tlfong01
    Aug 27 '20 at 8:00

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