Some companions to this work:
1. Wifi sensing from academia, particularly in the ubiquitous computing community- Shwetak Patel's group in Washington [1], Dina Katabi's group in MIT [2], Patwari's group in Utah [3], etc.
2. MIT OCW on how to build a radar system with advanced [4] capabilities http://ocw.mit.edu/resources/res-ll-003-build-a-small-radar-...
[1] https://ubicomplab.cs.washington.edu/
[2] http://groups.csail.mit.edu/netmit/wordpress/projects/projec...
[3] http://span.ece.utah.edu/neal-patwari
[4] I use 'advanced' in the sense that it is way, way, more sophisticated in its use of math and signal processing/machine learning/linear algebra algorithms than your standard automotive speed monitoring radar.
As before, this is totally awesome---until the FCC (or other national spectrum regulator) shows up at your door...
Here is an assortment of things that the author might be interfering with in the neighborhood of his 5.5 GHz carrier frequency: https://wirednot.wordpress.com/2014/01/07/what-else-is-in-th...
Some of this is the sort of stuff you really don't want to interfere with--both for safety reasons, and because of the likelihood of enforcement.
Next time I suggest that the author look into whether his jurisdiction will grant him an experimental license so he can do this legally. In many jurisdictions that is cheap and easy (unless, of course, you want to operate in a band where the interference risk is just too high).
Edit: I see the author is in Finland. Unfortunately for the author, I'm guessing this changes nothing since these frequencies are regulated both nationally and internationally. But it does mean that there is probably some local variation in the exact services that might be subject to interference. And who knows: maybe in Finland the 5.5 GHz band is a "do whatever you want at any power level you want" band. But I doubt it...
Even unlicensed, he has up to 25mw of power and 8.5db antennas (which with 25mw or less can give you upwards of a mile of clean signal), which may be sufficient. Hard to say.
And in the U.S. at least the bands around 5.5 GHz (the so-called U-NII-2 and U-NII-2 extended bands) are subject to lots of interesting rules for unlicensed operation, including the ability to detect and avoid incumbent RADAR signals. https://transition.fcc.gov/bureaus/oet/ea/presentations/file...
Of course, I know literally nothing about the Finnish rules that actually apply here...except that, thanks to the ITU, they probably bear some resemblance to the U.S. rules.
Here's a similar project which is in the 5.8 to 6 GHz range. With a little work, they could probably make it stay in the ISM band there. One big frustration of gigahertz RF work is that the test gear you need to see what's happening costs far more than the project. I tried to build a frequency-modulated LIDAR once, and ran into that.
[1] https://hackaday.io/project/1682-simple-low-cost-fmcw-radar
Yes, that is basically how it works. The system takes measurements at a series of slant ranges (called range bins) for each beam position. The returns from those range bins can be mapped to a physical location as long as the location of the receiver is known. Record enough beam positions in a line and you can map a 2D image.
Radar, SAR, and especially passive multistatic SAR are technologies that I'm sure we're going to see more of in future. Passive SAR (or transmitter-of-opportunity SAR) can be computationally expensive, but pieces seem to be there to build something that works really well.
So I'd hire him.
[1]: https://en.wikipedia.org/wiki/Young_Turks
edit: I assume that was a typo as it was edited to "young bucks" later.
Whippersnappers is perhaps a better fit.
