The use of surface acoustic wave (SAW) devices is a widely adopted method for implementing unique identification tags that operate completely passively and can be interrogated wirelessly. Interrogation can be done in the time- or frequency-domain, where in the latter case bandwidth is a restraining factor. Conventional signal evaluation is based on the fast Fourier transformation (FFT), which suffers from resolution limitations. Modern model-based frequency estimators have been investigated for SAW ID-tag identification. A state-space algorithm is applied to measured data and compared to FFT evaluation results.
In frequency modulated continuous wave sensor systems for object distance measurement, use of the fast Fourier transformation for frequency estimation is widely adopted because of its comparably low execution time and available implementations. Inherent resolution restrictions make modern state-space based frequency estimators a viable alternative to this approach. Estimation of the correct model order, crucial to accurate distance measurement when used in a setup with an unknown number of targets, may be avoided by using active transponders. In this paper, application of a state-space frequency estimator is investigated with the use of measurement data in a system with an a priori known number of active targets. Evaluation results are analyzed and compared to performance of the Fourier transformation.