MIMO Radar Antenna Arrays | Hacker News Reader

MIMO Radar Antenna Arrays

hforsten.com

98 pointsparsecs7 comments

Nice article! I used to work in this field and there is an insane amount of cool tricks you can do if you have enough signal processing available. The first (obvious) one is that, since you can switch beam direction as quickly as you can switch radio frequency (ie thousands of times per second) it is no longer necessary to give each target equal illumination time. It is for example possible to mostly focus on the missiles inbound to your vessel at mach 3 while still not losing track of all the other traffic in the area. You can't really do that with older mechanical antennas since the inertia would tear the assembly apart.

The second is "colored space" radar, where you arrange the phases and wavelengths in such a way that the same transceiver array can generate multiple beams with different frequencies in different directions, giving true parallel beamforming (not merely concurrent as in the first example).

Finally, though every textbook introducing these concepts uses transceivers arranged in a flat plane, that is not actually required. For example, the F-35 uses "conformal antennas" that are shaped like the rest of the airplane and uses a phenomenal amount of signal processing to convert the resulting signals back to "as if" the antenna had been a flat plane.

I have always wanted to experiment with these things and rectennas to power small UAVs from afar so that they never have to land, but never got around to it.

I have always been fascinated by powering devices with rectennas, but my research always turns up people “debunking” this, despite there being able research papers. Could you elaborate more on how you’d approach such a project?

Also may I ask what your current field is?

A lot of people with proposals in this direction (most with only vague understanding about how electricity works, sadly) are wildly optimistic about the efficiency of wireless power transfer and wildly pessimistic about the efficiency of physical wires. I don't think wireless power transmission will ever replace large scale power transmission for terrestrial applications for example. It is also not very useful for powering small devices in (say) a room because the rectenna array need to be "facing" the transmitter and you can't guarantuee that for a phone in a pocket. You can make it up by increasing the power, but it's easy to show that it would need to transmit dangerous amount of EM radiation to get a reasonable amount of power to the device(s) in all scenarios. Hence the debunking.

That said, if transmission efficiency is not your absolute main concern (such as would be the case when powering a drone) and you can control the attitude of the receiver array then it can absolutely be done. Apparently a Canadian research institute built a rectenna-powered plane all the way back in 1987 that could stay aloft for months. If I would go into a project like this it'd be interesting to see why they didn't continue with this and why "modern" long endurance drones typically go for solar cells on the wings instead. Tech-wise, getting some basic arrays up and running would be a good idea too. Finally, I can imagine that a certain amount of political goodwill would be needed as well, since high power phased arrays and long endurance drones have obvious military applications and most governments like to keep a tight lid on military tech (for good reasons).

Current field is working as a combined Ruby/SRE freelancer, helping local startups fix speed up their test suites and fixing the sometimes terrible SQL queries ActiveRecord can spit out if you are not careful. Quite different from my previous field but a lot more freedom :)

Oooh just give me a sensor array, infinite processing power and watch the digital beamforming, space-time adaptive processing, and millions convolutions dance...

Seems nearly impossible but it would be cool if SpaceX would open up access to the RF capabilities of their Starlink user terminal. Pretty impressive array for consumer electronics.

As to beaming power: Lasermotive worked on this problem for a while, but (to UAVs), but have recently renamed and are now working on delivering power over fiber.

The UAV power problem is still huge (for example, the military needing to keep defensive, electric, UAVs aloft indefinitely vs very short linger times.

https://en.wikipedia.org/wiki/Powerlight_Technologies

The folks at DARPA want to investigate the use of Machine Learning math and tools to control and process antenna arrays. See the Tensors for Reprogrammable Intelligent Array Demonstrations (TRIAD) program, referenced here:

https://intelligencecommunitynews.com/darpa-releases-triad-a...

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