I was watching a youtube video about the b2 this morning. It mentions that while it’s not completely invisible to radar, it only has a cross section about the size of a bee. It says that radars have to fine tune their displays to only show larger objects or else it would be too cluttered.
I guess my question is, why can’t they tune their displays to only show objects moving faster than ~ 300 mph?
In: Physics
Radars work by blasting out a radio pulse at a specific frequency that then bounces off of something and comes back. The radar knows when it sent the pulse, and knows when it heard the much much fainter return, and then calculates a relative location based off the time of travel of the pulse, and the angle it was looking.
Stealth or low observable is all about minimizing the radar returns. They do it through a lot of very technical and secret means but it basically boils down to shaping the aircraft to either scatter, absorb or redirect radar return energy away from the radar that is looking for it.
Different radars work at different frequencies based on what they are trying to do. Low frequency radars with huge wavelengths go very far and can see things coming from a very long way away but they don’t have as much resolution and they can’t get very precise locations. These are early warning radars because they alert the military that someone is coming. but it’s ambiguous what that thing is.
sam radars and fighter radars operate in higher frequencies with smaller wavelengths that can see very accurately but not nearly as far and give a precise enough quality track to guide a weapon.
stealth (more accurately Low Observable) technology necessarily has to be optimized against a specific frequency ranges based on what its trying to evade. different wavelengths of the pulses mean they will bounce off different parts of the aircraft, so although a B2 or F-22 will be stealthy across all spectrums it will be much stealthier in one specific spectrum. how it is designed is mostly based on the mission its expected to do and the threat it is expected to face. generally LO is more focused against the radars that can guide weapons because if they cant shoot you it doesn’t really matter if they detect you far out.
LO is designed to make sure that as much if the return as possible will not
bounce back at the radar. and the tiny amount that gets through will fall below the noise floor below which then radar cant see it. a doppler filter to see anything above 300 knots could work but now you have blinded the radar to anything slower and it is still going to be blinded by all the other much louder returns of other airspace users. its kinda like trying to see the light of a match when you have the sun right behind it. because of how faint the return is the aircraft would have to get very close before the radar could see it, effectively shortening the radar range.
also… i can make my relative closure shrink by not flying straight at the radar. i could be going 400 knots but if its at an angle to you your doppler radar would show much lower closure and id fall through the detection floor.
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