Phase stability comparison of SAW sensor evaluation with various CW type radars

The paper describes the comparison of three different types of continuous wave (CW) radars to interrogate surface acoustic wave (SAW) sensors. The CW types are as follows: a frequency modulated (FMCW), a frequency stopped (FSCW) and a switched frequency stepped (S-FSCW) radar. All types operate in the 2.4 GHz ISM band with a bandwidth of approximately 80 MHz. Whereas the sweep time of FSCW type radars typically is around 100 ms the FMCW radar sweep lasts only 100 mu s. Measurements of all three types have been taken in equal standard settings to evaluate their phase stability, important for high precision sensing. The S-FSCW shows overall the best phase stability. The FMCW has about a factor 5 less stability due to the fast sweep time, but can be improved by averaging considerably. Furthermore the influence of ambient temperature exposure of the electronics from -20 degrees C to +50 degrees C on the phase stability is presented in this paper. (C) 2010 Published by Elsevier Ltd.