Is It Possible to Determine How Far a Passive or Active RFID Tag Is from a Reader?

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Ask The ExpertsIs It Possible to Determine How Far a Passive or Active RFID Tag Is from a Reader?
RFID Journal Staff asked 4 years ago

For instance, if a tag were placed somewhere within a room, would a reader be able to tell where or how far away it was?

—Master

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Master,

This is a question we are often asked. Conventional passive low-frequency (LF), high-frequency (HF) and ultrahigh-frequency (UHF) systems are designed to tell you when a tag is inside a read field. They do not tell you that a tagged item is, say, 3 feet from the back wall of a room and 4 feet from the left wall. There are passive UHF solutions that used phased-array antennas to determine a tag’s location; these are accurate to within about 10 square feet (0.9 square meter).

Active tags transmit a signal, and several readers might pick it up. Software can then triangulate on the signal and use time of arrival, angle of arrival and other techniques to determine the tag’s location. These are also accurate to within about 10 feet.

If you require greater location accuracy than this, I would suggest an active ultra-wideband (UWB) system. UWB technologies employ a variety of frequencies to overcome the problem of the same frequency signal reflecting off surfaces and arriving at different times, which makes it difficult to pinpoint a tag’s location. UWB systems are accurate to within about 10 centimeters (3.9 inches).

—Mark Roberti, Founder and Editor, RFID Journal

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