I would like to utilize the antennas to interrogate tags that are very close to each other—only a few millimeters from one tag to the next. How would I do this?
A passive low-frequency (LF), high-frequency (HF) or ultrahigh-frequency (UHF) system allows you to read a large number of tags close to one another, in rapid succession, without much difficulty. But it sounds like you want to know the location of a particular tag versus that of another, which is something an RFID system cannot easily do.
Passive RFID technology can tell you that a tag is in the read field, but not where precisely where within that field. The only way to determine the location of one tag or another would be to create a grid of very small reader antennas. You would then know which antenna had read the tag, and thus where that tag was located. This is not usually very practical, however, since you would need to have the small antennas custom-manufactured—and you would also need several readers to run the antennas, depending on how many squares you had in the grid.
—Mark Roberti, Founder and Editor, RFID Journal
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