Is stealth fighter really invisible to radar?

It can be seen under any conditions, but it is only a question of the size of the reflection area. The reflection area is as large as a bird, which will be automatically filtered by radar filtering, so the radar interface will not be displayed. Actually, there is still a search.

Stealth fighter fuselage can't perfectly reduce the radar reflection area at every angle, usually the front and belly are the best, and the tail is the worst (this is the limitation of human science and technology, because it can perfectly avoid the shape of radar waves, or it doesn't conform to aerodynamics, it can't fly at all, or it can't stop once it flies with a rocket engine. )

(As for the online saying, "Have you ever seen a bird flying at supersonic speed?" This is really a joke. This kind of thing won't happen in reality. Air defense radar can sweep birds, but it will not show individual birds.

It doesn't really make much difference how high the radar flies (air defense radar is one or two hundred kilometers at a time, so how high can your fighter fly? Therefore, the extreme flying height of fighter is "face to face" for radar.

World War II paid attention to high-altitude and high-speed penetration, but air defense missiles developed rapidly. Humans have found that no matter how high and fast fighter planes fly, they can't beat missiles, so modern warfare pays attention to low-altitude penetration.

Yes, it is easier to avoid the radar when flying lower, because the radar is usually tilted for a larger airspace search range, which will lead to the problem that low altitude may become a blind spot, so fighters usually use low altitude penetration when entering enemy territory. Of course, this operation depends on the target. It is very useful for small countries without perfect air defense system. For a big country, it is possible to look up and down.

The air defense system of a military power is omni-directional, which can be seen from space to the ground for several kilometers. There is a big "peach pit" on the top of a hill in Baiyun Mountain, Guangzhou. This is an S-band low-altitude blind radar, which can detect "DJI" ...

Unless you can fly the plane at an altitude of 1 km from the ground, you will not be found by it, but will become "visible to the naked eye")