Why is radar hard to detect stealth aircraft while satellite telephones easily capture signals below the thermal noise floor?
In: Engineering
Radar does detect stealth aircraft. Every single one of them, and at great distances. They are not invisible to radar.
However thier designs involve materials that absorb radar, and deflect it away instead of returning it to the radar station.
This results in a much smaller return to the station, often similar to the return of a large bird like an eagle it flock of birds. So it’s disguised and often filtered out to remove thousands of false positives.
Low reflective paint on aircraft absorbs an amount of the radiation and the design is usually done to minimise reflection of rays too, so rather than reflecting the rays they scatter when they hit the hull.
Satellites can ‘see’ all of the points of transmission that they are trying to pick up. Sometimes this is outside of their range, but on a good day with the right background material (salt water is a good reflector) they can pick up more than intended.
Stealth aircraft use several different means to be hard to detect. Their surface is structured in a way that radar waves are only reflected in 4 directions, and then use a flightplan that avoids sending a reflection in the direction of a known enemy radar station. They also absorb as much radiation as possible through special materials and a fine structure of different materials under the surface.
And it’s a lot different to find a signal that is designed to be found in a noisy background compared to basically a tiny noise spike in a noisy background
Think about driving your car late at night. You see a car way off in the distance. You can see its headlight brightly, but your head lights are only illuminating the road just in front of you. Your lights appear just as bright to the other driver, in order to see that car if its lights were off it needs to reflect enough light back at you for you to see, and it is only being hit with a fraction of the light your headlamps produce, since most of it doesn’t hit the other car. This is kinda the same with radar. The signal has to be sent out from the radar dish and they are looking for the tiny reflection back. A stealth aircraft isn’t designed to not interact with radar, it does. It’s just shaped in a way that most of the radar it reflects goes up and away from the source.
Edit: typos
Because stealth aircraft like the F-117 are designed so they reflect the radar signal away, at a completely different angle.
The F-117 still receives incoming radar it’s just that the radar reflection is never seen by the enemy radar set.
The F-117 does this by being constructed from flat surfaces that reflect the radar in one direction only. Curved surfaces would reflect radar in all directions.
Technically no aircraft is 100% invisible. They minimise their radar signature. Some have the same radar signature as a seagull. As soon as the aircraft opens bomb doors or lowers undercarriage or even carries external stores like the F-35 then the radar signature becomes less stealthy more observable
Stealth aircraft are specially designed to reflect radar signals in the wrong direction, and absorb some of it too (Meaning the few signals that are reflected back will be much weaker). Most modern military radars can be adjusted to detect stealth aircraft, the problem is that it significantly increases the chances of false positives as the noise floor is much lower. So things like birds start showing up as objects on the radar.
Satellite phones only listen on a specific frequency. So they do not need to search for tiny dots on a radar return, they just tune in on whatever satellite they’re programmed to.
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