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SDR based RFID reader for passive tag localization using phase difference of arrival techniques

This paper presents a passive radio frequency identification (RFID) reader for a two dimensional localization of tagged objects in the ultra high frequency (UHF) band. The presented prototype is capable of simultaneously estimating the direction and the range of an object. This capability is provided by a single input multiple output (SIMO) antenna configuration in combination with phase difference of arrival (PDOA) techniques. The core of the prototype is a flexible software defined radio (SDR) that allows rapid prototyping and thus a fast system verification. The reader operates at three frequencies that makes the tag localization more robust, especially in multipath environments. The reader verification is shown by measurements in an anechoic chamber. An initial angular accuracy of 3 degrees for the tag direction and 23 cm for the tag range is accomplished in this first stage of the prototype development.