The only passive tag I know of that operates at 2.4 GHz is Hitachi‘s µ-chip (Mu chip), which has a read range of a few millimeters because the antenna is built right into the tiny chip (see Hitachi Unveils Smallest RFID Chip and Hitachi Unveils Integrated RFID Tag).
There are battery-assisted tags that operate at 2.4 GHz (see Internorm Finds RFID Does Windows). Idmicro’s Remote Intelligent Communication tag is also a battery-assisted tag, and has a read range of 30 feet or more (see Tracking Skiers for a Good Cause).
A Silicon Valley startup company known as Tagent has developed an ultra-wideband (UWB) system that can be read from long distances, but it requires nodes to emit energy at 5.8 GHz to power up the passive tags so they can communicate with an interrogator (see Chip-size Passive RFID Tag Promises Long Range).
—Mark Roberti, Editor, RFID Journal
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