Here is Part IV of Chapter 3--Radio Basics For UHF RFID--from The RF in RFID: Passive UHF RFID in Practice. Written for the electrical engineer but not the RFID expert, Dr. Dobkin explains what to expect, develop, and use while implementing an RFID system.
Passive and semipassive RFID tags do not use a radio transmitter; instead, they use modulation of the reflected power from the tag antenna. Reflection of radio waves from an object has been a subject of active study since the development of radar began in the 1930s, and the use of backscattered radio for communications since Harry Stockman's work (See Chapter 2) in 1949.
