Passive Radar Stealth possible?(Minimizing RCS needed)

T75

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I'm curious as to what RCS would be needed to beat the detection threshold for K and KA band radar police radar. I understand that they can detect objects as small as baseballs but such an object has an RCS that is only detectable well within 200 meters. What level of granularity are these handheld radar devices able to scope out? Such as a single welded seam between two angled pieces of metal, would that get identified and clocked?

I'm asking this with the intent to potentially modify a C3-C5 corvette with a minimized RCS that could give me more warning time if an officer picks me over other vehicles, but won't attempt it if these guns can detect a single poor weld on a reflective surface I put under the fiberglass body*. If having commercially available RAM on top of such points would change the outcome I'd like to know.

Thank you for any answers that are given.

*(I understand I couldn't have metal paint or anything that's reflective to radar on the fiberglass)
 

viggendriver

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It would be beyond the capability of anyone without very specialized equipment and material to actually stealth their car where it wouldn't be detectable. The biggest problem for most cars is the radiator. It's metal and typically facing forward. Vette's have it angled which reduces RCS but its not invisible. Modern police radars not only pick up the strongest signal but most these days have the fastest vehicle so you'd have to reduce your signature a lot. Radar bounces off *everything*....headlights, mirrors, turn signals, wheels, etc. etc. Your car looks a lot different to radar than it does aerodynamically. That slippery sloping shape probably has a big ass metal crash bumper underneath and that reflects a ton of radar. Even military stealth platforms require continuous work to maintain their low observable features. Unless you have a very fat wallet, RCS reduction is not a viable option.

IMHO the only way to defeat radar is jamming and that gets you in more trouble that speeding.
 

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Jon at Radenso

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I could answer this question but it would be low six figures in simulation time unfortunately. I have actually discussed this seriously with a few clients looking for a bespoke solution that basically had unlimited wallets and it is my belief that we could make a car with extremely low RCS with about $150-200k in engineering costs and about $200k in build and materials costs on top of the OEM car costs. And this is assuming the willingness to completely destroy the original car and rebuild basically every body panel on it to our exacting dimensions.
 

WildOne

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I've got a 74 Vette. While it has a lot going for it for stealth over other cars, there is not much practically that you can do to it to actually be useful for getting out of a ticket.
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I could answer this question but it would be low six figures in simulation time unfortunately. I have actually discussed this seriously with a few clients looking for a bespoke solution that basically had unlimited wallets and it is my belief that we could make a car with extremely low RCS with about $150-200k in engineering costs and about $200k in build and materials costs on top of the OEM car costs. And this is assuming the willingness to completely destroy the original car and rebuild basically every body panel on it to our exacting dimensions.
And don't forget that a car has to be driven in the rain, washed when it is dirty..... ;)
 
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Jon at Radenso

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And don't forget that a car has to be driven in the rain, washed when it is dirty..... ;)

Yup. And the requirement to basically continuously maintain it to preserve the stealth properties. It's just not practical for most people.

However, as I said there are a select few customers I have that the cost just isn't an issue for, and who could hire people to maintain them. In that case, the issue was for us that it was bad timing since it would be a serious investment in engineering on our part and it wasn't practical to push back our product plans further and divert half our engineering team for a couple hundred thousand dollar contract.

In the future though it is something I am extremely interested in trying as a fun experiment given the right partner, which I am pretty sure we have. Just need to wait until we aren't in the middle of a few product rollouts and dealing with such a difficult business environment.
 

T75

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Yup. And the requirement to basically continuously maintain it to preserve the stealth properties. It's just not practical for most people.

However, as I said there are a select few customers I have that the cost just isn't an issue for, and who could hire people to maintain them. In that case, the issue was for us that it was bad timing since it would be a serious investment in engineering on our part and it wasn't practical to push back our product plans further and divert half our engineering team for a couple hundred thousand dollar contract.

In the future though it is something I am extremely interested in trying as a fun experiment given the right partner, which I am pretty sure we have. Just need to wait until we aren't in the middle of a few product rollouts and dealing with such a difficult business environment.
I understand that a vehicles RCS could probably be reduced so drastically to the point where it's almost comical, I'm curious though as to the actual minimum amount of RCS that would be needed to actually beat radars at some arbitrary distance of around 500m-1000m. Is there any information out there that I can look at to figure out the bare minimum here?

Vette's have it angled which reduces RCS but its not invisible. Modern police radars not only pick up the strongest signal but most these days have the fastest vehicle so you'd have to reduce your signature a lot. Radar bounces off *everything*....headlights, mirrors, turn signals, wheels, etc. etc.
I understand the problem about the exterior features that may be a detected but many of those features can be minimized or mitigated entirely with shaped parts. Radar transparent surfaces such as the windshield and the blinkers can be coated to be reflective, in the case of the blinkers they can be angled. Tires can have hubcap radar absorbent material(RAM) coverings and have a the wheel well lined with RAM to minimize the signature along with the bottom of the car being lined with it(lol this is starting to sound a bit expensive). Is police radar so sensitive that a slanted board with RAM can be detected from 500m+ is more of the question I'm asking.

Thanks for your answers by the way, I'm going to keep looking into this for a bit and if I find any information I'll post it here.
 

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I understand that a vehicles RCS could probably be reduced so drastically to the point where it's almost comical, I'm curious though as to the actual minimum amount of RCS that would be needed to actually beat radars at some arbitrary distance of around 500m-1000m. Is there any information out there that I can look at to figure out the bare minimum here?


I understand the problem about the exterior features that may be a detected but many of those features can be minimized or mitigated entirely with shaped parts. Radar transparent surfaces such as the windshield and the blinkers can be coated to be reflective, in the case of the blinkers they can be angled. Tires can have hubcap radar absorbent material(RAM) coverings and have a the wheel well lined with RAM to minimize the signature along with the bottom of the car being lined with it(lol this is starting to sound a bit expensive). Is police radar so sensitive that a slanted board with RAM can be detected from 500m+ is more of the question I'm asking.

Thanks for your answers by the way, I'm going to keep looking into this for a bit and if I find any information I'll post it here.

The problem with this is that when you say things like "they can be mitigated with shaped parts," "the blinkers can be coated to be reflective," and "they can be angled" what you have to understand is that everything has to be simulated. The shape has to be precise, the angle has to precise, the radius of the bends has to be precise, the materials have to be entered precisely, the emitter has to be modeled, etc.

What you said is sort of kind of generally correct...but arriving at the correct shape of the parts would require at least a hundred grand in simulation time using software like CST Microwave Studio or HFSS. We would have to iteratively CAD model the car, import it to our software, run full 3d sims, and adjust and redo. For context, on a 64 core 3990X computer with 4 RTX 2080 TI a 3d sim of just our radar front end can take almost a full day. If you add in a full 3d sim of a car I can't even imagine what the sim time would be.

Radar is hard. And expensive.
 

viggendriver

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I understand that a vehicles RCS could probably be reduced so drastically to the point where it's almost comical, I'm curious though as to the actual minimum amount of RCS that would be needed to actually beat radars at some arbitrary distance of around 500m-1000m. Is there any information out there that I can look at to figure out the bare minimum here?


I understand the problem about the exterior features that may be a detected but many of those features can be minimized or mitigated entirely with shaped parts. Radar transparent surfaces such as the windshield and the blinkers can be coated to be reflective, in the case of the blinkers they can be angled. Tires can have hubcap radar absorbent material(RAM) coverings and have a the wheel well lined with RAM to minimize the signature along with the bottom of the car being lined with it(lol this is starting to sound a bit expensive). Is police radar so sensitive that a slanted board with RAM can be detected from 500m+ is more of the question I'm asking.

Thanks for your answers by the way, I'm going to keep looking into this for a bit and if I find any information I'll post it here.
You can coat, shape, whatever but you'd need a lot of money to cover everything. Heck, even the gap/seam between the hood and the car would create unacceptable reflection. The wheels are metal and radar is going to travel through the rubber and bounce off. Look at it this way, I've tracked people on bikes from 500+ feet away with radar. Can you get your car smaller than a bike? That windshield you want to angle? Better seal it to the vehicle with very expensive RAM because the entire windshield joint is a giant reflector. And that assumes you have access to effective RAM that covers K and Ka. Then like others have said, you'll need simulation and measurements. Ka test equipment is $$$$. There's a reason no one has done it before...it's not possible unless you want to design the car from the ground up as a stealth vehicle.
 

Yippeekyaa

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And if one were to succeed in making a vehicle invisible to radar, that moto cop with a laser gun will still get your speed in milliseconds rendering the effort moot.
 

T75

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You can coat, shape, whatever but you'd need a lot of money to cover everything. Heck, even the gap/seam between the hood and the car would create unacceptable reflection. The wheels are metal and radar is going to travel through the rubber and bounce off.
Thanks for answering my initial question partially, I was worried about the gap/seam between the hood along with the seams along other body portions of the vehicle. So there's enough sensitivity on these police radars to detect such small perpendicular surfaces it seems. that's pretty scary of a thought. Are there any resources that I can look at that could go more into detail on the sensitivity of their guns?
In regards to bikes being clocked I'm sure their RCS would be substantially easier to detect than a car driving with a slanted tinfoil wrapped cardboard board in the front of it due to their perpendicular surfaces. They probably have a higher proportional RCS than some sports cars at certain angles if not an outright higher signature.
The problem with this is that when you say things like "they can be mitigated with shaped parts," "the blinkers can be coated to be reflective," and "they can be angled" what you have to understand is that everything has to be simulated. The shape has to be precise, the angle has to precise, the radius of the bends has to be precise, the materials have to be entered precisely, the emitter has to be modeled, etc.

What you said is sort of kind of generally correct...but arriving at the correct shape of the parts would require at least a hundred grand in simulation time using software like CST Microwave Studio or HFSS. We would have to iteratively CAD model the car, import it to our software, run full 3d sims, and adjust and redo. For context, on a 64 core 3990X computer with 4 RTX 2080 TI a 3d sim of just our radar front end can take almost a full day. If you add in a full 3d sim of a car I can't even imagine what the sim time would be.

Radar is hard. And expensive.
Alright I think I haven't been fully transparent with what I'm attempting to ask/do here, my bad. I'm looking into potentially making a car body that can beat radar only at a very specific threat axis(frontal, I understand covering all angles would be extremely costly) which I was thinking could be relatively easy. Worst case scenario I am thinking would be to make a shaped front end as a low to ground wedge and simplify the surface geometry to match that profile with the windows. Is such a simple shape required to have such complex calculations? would the front edge lip of the wedge and seams be such a factor at play that I'd need to simulate even those to get a relatively accurate result?

*lets even remove wheels from the answer here which I admit are probably going to be the largest problem if someone attempts a stealth vehicle and would have to be addressed separately.
 

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Electromagnetic energy is very difficult to visualize and does not behave the way you would think. There's a reason everyone uses it to detect aircraft etc. We pick up aircraft at 200+ miles because it bounces off every part of an aircraft. Think about how little energy needs to get back to a receiver to pick it up. Then you have to understand how RF energy acts. Edges lead to corners and corners are death. Any time you have a joint/gap/seam you have a major problem. Then you have to determine how your car really looks to a radar. It's not the same as visually. Different materials reflect different wavelengths then factor in all of the ducting, etc. used for cooling, etc. Getting the ground wedge close to the ground isn't going to help much because you are still going to have the edge of that wedge creating a pretty decent reflector...then all of the RF bouncing around underneath. If you had some good modeling and RAM you could try sawtoothing that edge which would help. You can do a pretty good job with RCS *reduction* but getting to the point where a receiver can't detect you is very very difficult and expensive. The one advantage you might have is that you are only looking at 2 frequency bands and they are way up there in the GHz range. For the money, go put a kick ass lawyer on retainer and then buy a supercar....you'll have money left over:)
 

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Getting passive RCS reduction done right on a car would be an expensive, but not impossible endeavor. Trying to apply low observable techniques isn't quite as easy as running model simulations. In the real world, stealth is 85% shape, 15% materials. Just like what viggendriver posted, joints, gaps, and seams will be a major problem. Precision and tight controls when it comes to manufacturing and finishing is absolutely critical for low RCS. Step heights in the range of 15 mil can give off a strong signature. Surface roughness can also create noticeable signatures. RCS management has shifted its priority from lowering overall 360 degree signatures towards directing known RCS signatures into specific areas. For most cars, this "could" practically be done by faceting known hotspots up and away towards the sky.

Any time a surface presents a perpendicular face toward a target, there will be a strong return signature - headlights, grills, A-pillar, lower splitter, mirror caps. Keep in mind, it doesn't have to be a flat perpendicular face. Any curved surface will return back to the source. Wheels, from the front sector, is the least of your issues (unless you have big spacers or really wide tires).

Keep in mind, low observable does not mean invisible. Imagine having an extremely bright flashlight at night. A car painted black at a far distance is going to be hard to see, even with an extremely bright light. That same car is noticeable at much closer distances.
 

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I understand that a vehicles RCS could probably be reduced so drastically to the point where it's almost comical, I'm curious though as to the actual minimum amount of RCS that would be needed to actually beat radars at some arbitrary distance of around 500m-1000m. Is there any information out there that I can look at to figure out the bare minimum here?

Some starting terms for you to Google (or search engine of your choice): "Radar Range Equation", "Calculate RCS of a shape", "RCS gain" (or alternately, "Gain of RCS"), "RCS reduction techniques", "how to measure RCS". Here is a link to a handbook on my web storage site that will introduce you to some of the basics (sorry, this is the old version of the handbook, there is a newer version to be found if you search): http://www.tokenradio.net/Radio/SharedFiles/InfoTfer/1037.pdf

The following is going to sound flip, but it is not meant that way. Several facilities offer training on the concepts required. For example, if you can swing it, Georgia Tech (just naming one of many possible places) has both a fundamentals and advanced short course on Radar Cross Section Reduction (RCSR). If you can get into those then you might also consider the courses they offer on Infrared and Visible Signature Suppression, since the information there can apply to LIDAR. On the total cost scale of the effort you are discussing the course cost is miniscule. The cost of the courses is not the larger problem, it is the access that can be hard to line up.

What bare minimum are you looking to have? Are you looking for the smallest RCS that can be speed checked at a specific range? Or are you looking for how much reduction will have to be applied to a specific vehicle to achieve some minimum "safe" range?

In the case of the first number, the smallest RCS that can be tracked at a specific range, that will be gun dependent. The radar range equation can give you this answer, but you need to know some specific values for the gun type/make/model in question. Not all guns, even in the same frequency bands, will have the same answer. You could make some educated guesses on the parameters based on the technologies used and get pretty close. But close is like a kiss from your cousin, it may feel nice but something just ain't right there.

In the case of the second number, how much will you need to reduce the RCS of a vehicle to make a quantified change in the tracking range, that is easier to describe, but not simple to do. We know, for example, that a total RCS reduction of 6 dB will halve the detection range of a vehicle. And that if we can reduce the total RCS on the desired angle of arrival (RCS is very tied to view angle) by 10 dB then we have reduced the maximum tracking range to about 32% of what it is for the untreated vehicle. If you can make a 20 dB RCS reduction that is huge, your ~10 square meter (RCS, not physical size) car can now be around 0.1 square meter, and the max detection range is reduced by about 90%, an exemplar 2 km max detection range becomes 200 meters. A more manageable 14 dB reduction reduces max detection range by about 80%, a 2 km max range becomes more like 400 meters.

Modeling and simulation is all well and good, and is a great starting point, but at some point you have to do real measurements. And that means an RCS range of some kind, possibly including an anechoic chamber. You need an instrumented radar in the frequency range(s) of interest to check that what you think is happening is really happening. You might be able to lease access to facilities, or it might actually be cheaper just to build it all up.

I understand the problem about the exterior features that may be a detected but many of those features can be minimized or mitigated entirely with shaped parts. Radar transparent surfaces such as the windshield and the blinkers can be coated to be reflective, in the case of the blinkers they can be angled. Tires can have hubcap radar absorbent material(RAM) coverings and have a the wheel well lined with RAM to minimize the signature along with the bottom of the car being lined with it(lol this is starting to sound a bit expensive). Is police radar so sensitive that a slanted board with RAM can be detected from 500m+ is more of the question I'm asking.

Thanks for your answers by the way, I'm going to keep looking into this for a bit and if I find any information I'll post it here.

You have received some really good information from previous responses in this thread. But let me address some of the things you said directly.

"Radar transparent surfaces such as the windshield and the blinkers can be coated to be reflective, in the case of the blinkers they can be angled." What you are talking about is a surface treatment that forms a high pass filter, it allows light to pass while reflecting RF of the desired frequencies. OK, that can be done. But now the transition from that material to the skin of the vehicle creates a problem, this will cause a reflection by itself. The transition from the reflective windshield material to the body of the car will be a straight edge, or worse yet a curved edge, that will reflect energy orthogonal to that edge. You control this a couple of ways, you can reduce the reflections at this transition, and you can redirect these reflections. Reduction involves multiple techniques including things like smoothing surface wave flow and reduce impendence bumps. You might opt for intentional transparent sections that lead to controlled terminations, i.e. you can't make the surface shape what you want it to be, so you make it transparent to RF and put the controlling shape / material behind it.

"Tires can have hubcap radar absorbent material(RAM) coverings and have a the wheel well lined with RAM to minimize the signature". Great, what about the radar reflective construction internal to the tire? Steal belts and the like. What about the internal rim of the wheel? I bet that makes a nice corner reflector. Remember that even if the wheel is tucked completely into a wheel well, and skirts / pants prevent much of that wheel from being seen, some part of that wheel is visible, and even if not directly visible, scatter, from the ground or from your controlled surfaces, will reflect off that wheel. Once you have all the direct line of sight reflections under control then you still have to deal with scattered reflections.


"along with the bottom of the car being lined with it(lol this is starting to sound a bit expensive)." I don't really think you have a concept, yet, of the real cost of trying to do what you are describing. Or how fragile such a installation might be.


"Is police radar so sensitive that a slanted board with RAM can be detected from 500m+ is more of the question I'm asking." No, it is not that sensitive, you absolutely could create a barrier on the front of a vehicle that would prevent a police radar from getting a speed reading until very close. If you are willing to go to that level then the problem becomes things like reflections under, around, and in the vehicle. But realistically making such a board, or combination of boards, that is reduced RCS by enough to matter, and have required things like windows, lights, wheels, and spinning axles, not offer reflections to direct or scattered energy, is tough. Not impossible at all, but not simple.

T!
 

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