Are there any cheap, effective solutions that can determine a tag's distance within a few centimeters? If so, do any use a single reader and no additional antenna, and no GPS?
There is currently no "cheap" system for determining, with precision, a tag's distance from a reader. The received signal strength indicator (RSSI) is not extremely reliable or precise, due to the fact that signals can reach the reader antenna after bouncing off the floor, the ceiling or metal objects. In general, passive RFID systems are designed to tell you that a tag is within the read field, or that it has passed through a doorway. They are not designed to indicate precisely where an object is located. Phased-array antennas can determine a tag's distance in three dimensions, but such systems are more expensive and are not precise to within a few centimeters.
—Mark Roberti, Founder and Editor, RFID Journal
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