A mm-wave RFID system with locatable active backscatter tag

Precise localization of an object with attached RFID tag is required for many future applications like the internet of things, augmented reality or distributed sensor networks. Especially precise medium range localization in dense multipath environments places high demands on the capabilities of RFID tags, which are severely limited concerning complexity and power consumption. Regarding range coverage, active backscatter transponders significantly reduce path loss in comparison to their passive counterparts. This is particularly important at high frequencies, which are attractive since their regulatory constraints offer larger allocated bandwidths compared to lower frequency bands. Therefore, with mm-wave transponders, ranging resolution, data throughput for RFID communication and multi user capability can be improved without accepting range limiting RF power restrictions like in ultra-wideband systems. In order to achieve a measurement range in the order of 10 m with a tag featuring limited complexity and power consumption, the switched injection-locked oscillator is proposed as backscatter transponder technology, which has already been successfully applied to lower frequency localization systems [2]. In contrast to a simple linear amplifier based approach, it offers much higher single stage gain in the order of about 60 dB when switched on. Furthermore, aliases caused by the switched operation allow suppressing passive reflections of the RFID reader's signal completely. In this paper, a complete 34 GHz FMCW RFID ranging system concept and demonstrator implementation based on the switched injection-locked oscillator are demonstrated for the first time. The theoretical expectations regarding the operation principle are verified experimentally and the performance of the demonstrator implementation is evaluated. Measurement results in an indoor multipath indoor environment deliver an accuracy of about 3 cm within a range of 1 to 6 m.