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How Many Antennas Are Required for Localization?
Would UHF active tags be accurate to within 1 foot at a distance of 100 meters (328 feet)?
The number of antennas required depends on the type of radio frequency identification system used. There are phased array antennas that are able to locate a passive ultrahigh-frequency (UHF) transponder in three dimensions with a single antenna. By contrast, a conventional passive UHF reader with a patch antenna has very little ability to locate a tag. One knows the tag is in the read field if it is being read and the received signal strength indicator (RSSI) can give you a rough idea if the tag is close to the antenna or not, but multipath limits the ability to locate a tag precisely within the read field.
Some active RFID systems use triangulation, so they require at least three antennas. Other systems measure the time angle of the signal arriving and the time it takes for the signal to arrive, and can locate a tag using two antennas. The only active RFID technology that can locate a tag to within 1 foot is ultra-wideband (UWB), which uses signals at different frequencies to compensate for multipath and achieve a high level of accuracy.
—Mark Roberti, Founder and Editor, RFID Journal
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