Contactless radiation pattern measurement method for UHF RFID transponders

Uncertainty analysis of intermodulation-based antenna measurements

“…A limitation in the bistatic setup is the variability of the input power. The multistatic setup of [7] would avoid this problem but we have used the bistatic setup due to the simpler mechanical construction. This requires that the input power of the system is adjusted iteratively based on the gain of the AUT.…”

“…The total received intermodulation response consists of the transponder response from (1), noise, and the inferference from (7). When the SINR is low, the interference will degrade the measurement result, as illustrated at specific angles in Fig.…”

“…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.…”

Characterization of Transponder Antennas Using Intermodulation Response

“…Another contactless measurement method is the intermodulation measurement technique, which was used to measure the radiation pattern of a UHF RFID transponder in [20]. In this technique, the transponder is illuminated with two closely located frequencies f 1 and f 2 .…”

“…Due to the inherent nonlinearity in the transponder, it scatters back a signal containing intermodulation frequencies nf 1 ± mf 2 of the excitation signal (n and m are integers). In [20], the idea of the method is shortly described and the method is experimentally demonstrated without detailed analysis or considerations.…”