Ultra-wide-band SAW RFID/sensors

During 2-year project "SAWtag" supported in frames of French program "Chare d'Excellence" a SAW tag and sensor system operating in the Ultra-Wide-Band (UWB) frequency range has been developed. Often SAW tags and sensors operate in 2.44 GHz ISM band using relatively narrow bandwidth B=82.5 MHz. The characteristics of these devices can be improved using UWB technology. We have developed two prototype devices operating in 200MHz - 400 MHz and 2000MHz - 2500 MHz UWB frequency ranges. A UWB interrogating device (the "reader") operating in continuous wave radar mode for 2.0-2.5 GHz range was developed and manufactured by T. Ostertag. The remote measurements show compressed RF pulses of about 2 ns duration, which include unique RF filling of a few sinusoids with amplitude modulation. Precise measurement of the pulse position is possible by correlation methods, avoiding the phase ambiguity problem. The temperature is measured with a precision of about 0.1 degrees C. This correlation method works even in an environment with strong reflections from metal objects. The short compressed pulses allow measuring a number of sensors simultaneously. For tag application, we measure and identify three different tags at the same time without a collision problem, and this number can easily be greatly increased. Using of Hyperbolically Frequency Modulated (HFM) signals in SAW-tags is also discussed. A UWB SAW-tag with extremely small chip size (0.8mm x 2.1 mm) has been demonstrated. We also briefly discuss the development of 6GHz SAW-tags.