Harmonic transponders: Performance and challenges

Abstract

Performance of a harmonic transponder strongly depends on the properties of the antenna and diode used, which makes finding a good combination of them very important. For a transponder with a fixed antenna geometry, the effect of different diodes is analyzed through electromagnetic simulations and theoretical calculations. The antenna used in the transponder is directly matched to the impedance properties of a particular diode. Effects of both detector and varactor diodes on the return loss characteristics of the antenna and the obtainable transponder response are observed. Criteria for selecting a suitable diode are given. Benefits and drawbacks of using different antenna matching techniques are discussed, and principal design steps are given both for transponders matched directly to the antenna and for transponders with external matching circuits.