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How can a RFID UHF (Ultra High Frequency) antenna read a LF (Low Frequency) tag?

I have a antenna designed for UHF made in China, but it can read every tag I have tried (UHF, LF, HF), I don't know why.

The model number of the reader is L6012-L.

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    \$\begingroup\$ All of the terms here and the associated cause of an antenna working that way should not require any explanation for someone that knows RFID well, the downvotes are a bit surprising as this question is clear to someone who has worked with RFID as @philFrost and I seem to both have. The english needed a little clarity, but you cant expect the poster to come back and magically fix it if they are not an english expert, someone else can edit and make that clear for them. \$\endgroup\$ – Kortuk Feb 14 '13 at 0:20
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    \$\begingroup\$ Actually I've never worked with RFID and I thought it was a very interesting question :) \$\endgroup\$ – Phil Frost Feb 14 '13 at 4:29
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Generally RFID operates on near-field interactions. This is language that make something simple sound much fancier then it is. When you are in the near field of an antenna any coupling is due to capacitive and inductive coupling.

Most antennas for such a system are actually just large loops of wire and the tag often has a similar construction. The communication is exactly like coupling an AC wave through a transformer. So the different frequency still works through the transformer. The only issue you will have is if the frequency is too high to couple efficiently.

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