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In this paper hardware and software aspects for the precise wireless interrogation of SAW delay line sensors by means of frequency-modulated continuous-wave (CW) interrogators are summarized. The generation of the interrogation signal as well as concepts for the frontend are treated. Advanced concepts, namely switched variants of CW based interrogators are introduced. The signal model and the appropriate maximum likelihood estimators (MLEs) for the unknown parameters are derived, as well as achievable evaluation accuracies by means of the Cramer-Rao bounds stated. Finally, a multi-antenna reader system is used for SAW interrogation by means of digital beamforming (DBF). Beside the basic DBF principles, measurement results of the interrogation of spatially separated tags will be shown.
Frequency Control Symposium, 2008 IEEE International
Date of Conference: 19-21 May 2008