Spatial Fading in Retrodirective Channels: An Experimental Study

Simple, low-power, reliable backscatter communication systems must overcome the severe, double-fading nature of the backscatter channel. In this article, we show experimentally that when a conventional transponder is replaced by a retrodirective transponder in backscatter systems, those deep fading nulls are reduced by as much as two orders-of-magnitude. We consider three multipath scenarios all of which show a pronounced link-reliability improvement with a retrodirective transponder compared to its standard non-retrodirective counterpart. The measurements also reveal that by comparing the best case scenario of the two transponder designs under 0.001 outage probability, the retrodirective transponder requires only a 13-dB fade margin while the conventional tag requires a 34-dB fade margin - a significant improvement that would be a key enabler for next-generation backscatter systems.