I had no idea what a circulator was or what purpose it served. The wikipedia link has a good description of what it is, and the pdf link is a paper about how to achieve full duplex radio operation, and shows where the circulator fits into the picture.
My initial impression is that this is a very significant advance; enabling full-duplex on a single frequency band effectively doubles the communication bandwidth. But, I'm not sure if this translates to the real world.
Not clear how this is different from any other Wheatstone bridge-like structure used for directional sensing at microwave frequencies. Lower loss, presumably? Active circulators by themselves aren't new ( https://www.google.com/?gws_rd=ssl#safe=off&q=wenzel+active+... ).
This is not an active circulator, there are no amplifiers. It's a parametric-modulated circulator - the capacitance is modulated. Not a new concept in microwave engineering. Not very useful in real-life: the PR-heavy letter neglects to mention (1) the poor instantaneous bandwidth <0.5% (figure 4c), (2) the poor linearity / poor power handling: Vm and Vdc are few volts in high-Q environment, which translates into maximum power handling well below 0dBm (3) the high sensitivity to analog component variation (fig 4c again) - not something you want in mass-produced components operating at commercial/industrial temperature ranges.
They neglected to mention the power level they used to measure the S-parameters in the letter or the supplementary material. No self-respecting RF engineer would forget to mention power levels - it again hints at very poor linearity / poor power handling. Typical university "research".
1. https://en.wikipedia.org/wiki/Circulator
2. http://web.stanford.edu/~skatti/pubs/sigcomm13-fullduplex.pd...