RFID Tag Antenna Performance Metrics

Hello! We've just gone through the halfway point presentation of our project regarding RFID systems, which involved simulating Passive UHF RFID Tag Antennas in different environments. We used HFSS and the S11 parameter to determine the antenna's performance.

However, we were informed that the S11 parameter is a poor way of determining the the tag antenna performance, since passive rfid tags use backscattering. Can someone enlighten me regarding this matter? If it's true, then how do we best measure tag antenna performance in HFSS Simulations? We used a lumped port for our signal source, by the way.

You may mis-understand your friends' suggestions. It's right UHF RFID tags use backscatter to communicate with readers. However, the matching between tag chip and tag antenna still plays an important role in their performance. What needs to be pay attention to is that S11 generated by HFSS automatically cannot be used directly in case of UHF RFID tags, since the impedance of tag chip is complex instead of the classical 50-ohm. You need to define equations to calculate the power transfer coefficient so as to measure the tag performance. In addition, the best way to determine the tag performance should be measurement or real-world test, since there are more or less something missing in the simulation.