Lighter, Cheaper Radio Wave Device Could Transform Telecommunications | Hacker News Reader

Lighter, Cheaper Radio Wave Device Could Transform Telecommunications

utexas.edu

73 pointsshitehawk6 comments

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.

1. https://en.wikipedia.org/wiki/Circulator

2. http://web.stanford.edu/~skatti/pubs/sigcomm13-fullduplex.pd...

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.

Can any RF engineers comment on this?

No. The circulator itself is not a new invention, this is just a new way of building them.

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+... ).

the Nature article linked in the parent link probably has more information:

http://www.nature.com/nphys/journal/vaop/ncurrent/full/nphys...

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".

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