| In order to obtain the exact time delay of pulses in the surface acoustic wave (SAW) based radio frequency identification (RFID) at unknown temperature, we propose a method for obtaining a high phase ambiguity resolution by measuring group delays and constructing some restriction on the exact positions of reflectors. To define the restriction parameters for a SAW RFID system with large code capacity and reliable identification, it is imperative to have a priori knowledge on the errors of group delay and phase. In this paper, we present the experimental and simulation errors for both phases and group delay, originated from the design procedure, the temperature effect, the fabrication process and the measurement. The temperature range in our investigation is -5-45°C. The average error of phase delay is about 4°; the maximum error of phase delay is about 16°. The maximum error of group delay is about 4 period |