Characterization of Transponder Antennas Using Intermodulation Response

The intermodulation measurement technique enables measuring transponder antennas without any cable connections. This contactless technique exploits the inherent nonlinearity of the transponder to generate intermodulation products that can be measured. In this paper, we relate the transponder antenna properties to the intermodulation response, and use this relation to calculate the gain and impedance matching of the transponder antenna. Additionally, we consider the limitations of the measurement method and present three different measurement geometries for measuring the radiation pattern. The presented equations and methods are experimentally verified by measuring an example harmonic transponder.