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I've just started working with weather radars and such. With weather radars, it is possible to detect bird migrations with a specific algorithm and a lot of information about birds, but it would be a problem to detect a single bird (depending on the bird size) because of the radar's resolution.

I am wondering, if you have a place or a secret base that you don't really want the population to see whats in that area and take photos of the inside of the area or spy, is there a way to detect small drones with radar signals if you pack a few radars around your place or military base? If so, how?

Pondlife
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user16513
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    For what I know, this could better fit in Physics.SE – SMS von der Tann Aug 20 '16 at 15:14
  • From what I know of radars, it all depends on the frequency of the radar. High frequency = small wavelength = higher resolution = you can see drones and other small things if your radar has a high enough frequency (Which also means you need more power to run it). – SMS von der Tann Aug 20 '16 at 15:17
  • Drone can be seen, depending on many conditions. Some aircraft are designed to be nearly invisible to radar, so the same can be done to drones, and that would work even closer to the radar system. This already exists. – mins Aug 20 '16 at 18:42
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    I won't post an answer, since I hope that we have a radar expert here, but from my knowledge, this would highly depend not only on physics, but on the settings of the actual radar system itself. For example, it can happen that a radar designed to look for something else notices the drone, classifies it as clutter and doesn't show it at all. Also, again depending on system type, a radar might have issues with targets with close range, because it takes a bit of time to switch from transmit to receive. There are commercial radars that can detect crawling infantry, for example FLIR Ranger R2. – AndrejaKo Aug 20 '16 at 18:44
  • @AndrejaKo: Good point on the radar software settings, but a FLIR uses body heat for detection, so it does not qualify in this context. – Peter Kämpf Aug 20 '16 at 18:47
  • @Peter Kämpf No, I meant FLIR as a company, not as a technology type. The company makes radars (well at least markets under its brand) as well as cameras and they have some systems that can even integrate both into "complete solution". – AndrejaKo Aug 20 '16 at 18:49
  • @AndrejaKo; You're right, I should have googled that before posting. The R2 operates at almost 40 GHz where the atmosphere is relatively opaque, so its range is severely restricted. But it is a radar. – Peter Kämpf Aug 20 '16 at 19:15
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    Planning to fly your quadcopter over Area 51, are we? – Romeo_4808N Aug 20 '16 at 19:19
  • I wonder if it might be easier to jam a drone's control signals – TomMcW Aug 20 '16 at 19:33
  • @CarloFelicione This one? – SMS von der Tann Aug 20 '16 at 20:09
  • I might be wrong, but somehow I think it's probably easier to detect the signals being sent to and from the drone rather than trying to bounce stuff off it. Unless it's completely autonomous of course, in which case it appears your base wasn't secret after all... – falstro Aug 21 '16 at 08:28

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Yes, small drones can be detected by radar, if the radar is designed for it. Aveillant is manufacturing radars that have a high resolution and continously cover a volume of airspace in which it detects and tracks objects including drones. Their system was tested in Monaco earlier this year and they were able to detect small drones up to 5 km away. Later this year they will install a permanent radar setup.

The Gamekeeper radar is designed to detect targets down to 0.01m2 cross section and has a range of up to 5km. Holographic Radar technology does not scan across an area as a traditional radar does, but continuously floodlights a volume of space, gathering 3D position and motion information from all targets, all of the time. This gives a detection and tracking capability beyond that possible with other radars.

Source

The technology they use is different from typical primary radars used for ATC.

DeltaLima
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Depends entirely on the drones. If the radar system is known and the drone is designed not to be detected by this particular radar system, then the drone can only be detected in exceptional circumstances. Small size would be one way, but in order to be effective, big is better.

Detection has many aspects, and one of them is how soon detection happens. If all you need is to stay undetected while you approach the target, only the frontal aspect needs to be considered. If, however, you want to stay undetected for the whole mission, the task becomes much, much harder.

The radar systems in operation during the Eighties along the Iron Curtain could already detect single, large birds. Adding computerized signal processing and networking of several radar stations has improved detection performance many times over since then. See this question for more details.

Community
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Peter Kämpf
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Radar detection of rotorcraft may be done by looking at the Doppler returns and seeing double sidebands caused by advancing and retreating rotors. The same is true for quadrotor type drones, though the radar returns from small plastic rotors may be very small.

Mike Rogers
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    You may improve your answer by speaking about radar resolution, as mention in the question. – Manu H Jul 21 '19 at 12:01