"...What is the future of radar stealth? Two emerging technologies that may become used more widely are plasma stealth and active signal cancellation.
Remember how I said that radar wave cancellation works like noise-reducing headphones? The idea is that a wave of a certain profile, when mixed with a copy of that wave that is inverted or half a wavelength out of phase, is mostly cancelled out. Noise-reduction headphones work by “listening” to the ambient noise with a microphone, and then playing this noise to you but inverted and/or out-of phase, so that the noise it plays cancels out the real noise. Now, stealth aircraft skins are made of multiple layers, so that the radar waves bouncing off the internal layers are half a wavelength out of phase with (that is, an inverted form of) the waves that bounce off the surface. But what if an aircraft could sense the incoming radar wave and figure out what direction it’s coming from, figure out what the aircraft’s radar reflection wave would look like, and then emit an inverted / out-of-phase version of that wave? The first part – detecting the radar wave and where it’s coming from – is easy and already an important part of most combat aircraft’s defenses. The second part – figuring out what your reflection would look like to that radar and from that direction – is trickier but not impossible. The third part – emitting a radar burst that cancels out the original – is much harder, because this burst must stop as soon as the original burst ends, otherwise your plane is sending out radar waves that are not canceling anything out and so can act as a beacon, signaling enemy radars to your airplane’s presence and location. It is also extremely important that the emitted radar-canceling wave matches the naturally-reflected waves very well, otherwise instead of cancellation, you get MORE radar waves coming from your airplane. Because the direction, phase, and timing of the emitted radar waves must be very precise, this system is significantly more complicated than the noise-reduction headphones it mimics. However, there are unconfirmed rumors of such systems being in use on the Rafale (the latest French fighter jet) and on the B-2.
“Plasma stealth” is not as spectacular as it sounds. Basically, it has been found that ionized air does a good job of absorbing radar waves. I actually have personally worked with trying to ionize air flowing around an object, even a wing – in my case, though, this was done for the sake of aerodynamic advantages, not stealth. Still, the fact is, with the right electric field, air flowing over a surface can be ionized easily and with little power. All you need is a high-voltage electric field. (In my case, I used a high-voltage high-frequency alternating field between two conductive strips, one of them exposed on the surface and one of them hidden just under the surface no more than a couple millimeters away). The strong electric field ionizes the air that flows into it – pull electrons one way and atom nuclei the other way. But the field can be set up so that the ions don’t actually hit the electrodes (if the field’s frequency is high enough, for example, the ions just vibrate and don’t really move very far), so you only need really low currents – not much power at all. And you don’t have to ionize air right on the surface of the airplane: You could also have some air from the engine intake or exhaust be fed through a strong electric field somewhere inside the airplane, which would ionize this air, and then pump it out somewhere near the front of the airplane. From there, it would be blown back, bathing the airplane in a shroud of ionized air. Or some completely different ionization system could be used, I don’t know. But the point is, once you have ionized air around your airplane (something that is quite doable), it might be much harder to pick up by radar. Again, there is no evidence that such an idea is operational or that it is even being tested on real aircraft, but that doesn’t mean it’s not, and it might be in the future."
ето извадка из пресконфренции прес релиза нортропа по поводу будущее радалов малозачетных самолетов следующего поколения