Characterization of Transponder Antennas Using Intermodulation Response

Abstract

Abstract-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.

Uncertainty analysis of intermodulation-based antenna measurements

“…where P N is the noise power, L is attenuation before the receiver, |S 21 | is the coupling between the transmitter and receiver, and OIP 3,t and OIP 3,r are the third-order intercept points of the transmitter and the receiver [8].…”

“…The intermodulation measurement technique was introduced in [7] for RFID and was further developed in [8] to characterize harmonic transponders. It uses a nonlinear load to generate a response at the third-order intermodulation frequencies.…”

“…In this paper we take a further look at the results of [8], define the sources of uncertainty and calculate the total uncertainty in the obtained results. Uncertainty analysis is needed to estimate the measurement accuracy which is important for comparing…”

“…The generated intermodulation response is then recorded and used to characterize the antenna. The analytical response has been derived in [8] and it is…”

“…1 that depicts the bistatic measurement setup. For more details on how the theory was formulated, see [8].…”