Designers of the B-2 Spirit stealth bomber say that they used radar-absorbing surfaces and a weird shape to outsmart radar systems.
However, the more complicated and more disturbing answer is that the much-ballyhooed stealth design works only against a certain class of radar, and that the planes can be detected by newer radar systems. As a result, the bombers now “work” only when surrounded by radar-jamming planes.
This is nothing new. The original “radar-proof” aircraft had a similar problem. The U-2 spy aircraft of the 1950s were essentially gliders made of plastic and plywood that were powered by a jet engine.
They were designed to be small and light enough to cruise for long periods of time at very high altitudes (80,000 feet) that were beyond the range of anti-aircraft fire. However, after several flights, another unexpected benefit showed up: the U-2s weren’t being picked up by Soviet radar.
For more than four years, U-2s remained virtually unchallenged in Soviet skies. That invulnerability, however, came to an end after the USSR upgraded both its radar and its antiaircraft weaponry, and in May 1960, the Russians shot one down.
Pilot Gary Powers ejected and was captured, creating an embarrassing international incident for the United States. And so it goes with new advances in weaponry: it doesn’t take long before someone figures out how to beat it, sometimes accidentally.
For example, the illusory invisibility of the stealth system took a big hit in Yugoslavia in 1999 when a bomber was shot down by Serbian troops using an antiquated, low-frequency radar system that wasn’t fooled by its high-tech trickery.
Now most new radar systems use a mix of high and low frequencies, rendering the stealth technology increasingly obsolete.
This isnt quite correct. The Russians could easily detect the U2 from the outset (much to the dismay of it’s builders – Skunkworks/CIA)
I also dont believe they had upgraded their missiles to shoot down a U2, it was down a poor decision to re-flying the same route as in a previous mission so the Russians were able to figure out where the U2 was heading and time the firing of a barrage of missiles to close enough to the U2 and take it out.
The stealth fighter was designed in 1979 so for it to be (almost) beating radar from 1999 is still very impressive.
Take a look at the Skunk works book, very interesting stuff.