Here is Part VII 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.
All the calculations we've performed so far assume that a wave leaves the antenna and strikes the tag, interacting with no other objects. This kind of calculation is very sensible if the tag and reader are placed in a specially designed anechoic chamber, or perhaps suspended high in the air from (nonmetallized) balloons.
