The following is excerpted from Chapter 3: Radio Basics for UHF RFID from the Book, The RF in RFID: Passive UHF RFID in Practice by Daniel M. Dobkin. Order a copy of The RF in RFID: Passive UHF RFID ...

Tags use very little energy, as little as 500 miliwatts (a milliwatt is equal to one thousandth of a watt). The tag’s antenna can only capture a tiny portion of the energy of the reader. Much of it ...

I intend to use semi-passive tags, since I believe that if I use such tags with a passive reader, the range would be somewhat increased—but I don’t know by how much. Please correct me if I’m wrong; ...