2008: Josh Griffin built a custom 5.8 GHz down-converter and demonstrated tag gains at 5.8 GHz when small, multiple tags are modulated jointly. Thus, Griffin modulation was born!
Josh Griffin demonstrates how the modulation of two antennas beside one another with identical signals significantly improves the backscatter data link (contrary to conventional radio links). Not only does the extra antenna scatter more power (rather than simply re-arrange the gain pattern), but the additional scattered impart peculiar and improved fading behavior to a multipath channel.
Fun Fact 1: The 5.8 GHz slot antennas from this experiment are still used today in Georgia Tech ECE 4371 Antenna Engineering Lab.
Fun Fact 2: Although invented by Josh Griffin, an outstanding follow-up paper by GTPG alums Akbar and Morys explore the antenna patters in this IEEE APS 2012 paper. The gain pattern of a single antenna reflector (red hashed) vs the Griffin modulator (blue solid) is shown below.