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L.W. Mayer, A.L. Scholtz:
"Antennas and Radio Transmission in RFID Systems";
Talk: EEEfCOM - Workshop, Deutschland, Ulm (invited); 05-28-2008 - 05-29-2008.

A main task in designing a passive RFID (radio frequency identification) system in the UHF (ultra high frequency) regime is to evaluate the influence of the radio channel. In this talk we summarize the requirements of reader and transponder antennas and show examples of antennas that are used in state-of-the-art RFID systems. We focus on transponder antennas that are the weak point in the radio transmission because of their size constraints and their interference with materials in the environment. Furthermore, we present a method to determine gain, efficiency, and input impedance of such electrically small antennas.
To determine the transmission loss between reader and transponder antenna, we discuss measurements of a radio channel at 868MHz that have been performed at four different indoor sites. The results clearly show the transition between the near and far field of the antennas as well as the effects of fading. At the end of the talk we draw conclusions on the reliability that can be achieved in the four different environments.

http://publik.tuwien.ac.at/files/pub-et_13805.pdf