UHF passive RFID backscatter power transfer function and coverage area

The RFID tag backscatter transfer power function is estimated from various measurement results in our anechoic chamber for two brands of tags. The backscatter transfer power function turns out to not be directly proportional to input power and therefore it cannot be modeled as a constant radar cross section. Additionally it shows that the classic radar equation cannot be applied directly under the assumption of a constant radar cross section to estimate the round trip path loss between the reader and tag. The backscatter transfer power function can also predict received power at the reader and predict the coverage area of the system.