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US Army Developing Encrypted Radar Waveform (thestack.com)
An anonymous reader writes: The U.S. army is working on an innovative technology for masking radar emissions in contested territory and environments with heavily congested radio bands. Effective radar system performance is critical in military operations, yet remains a challenge in locations under attack or in areas of high traffic density. Army researchers have now developed a noise-encrypted radar waveform called Advanced Pulse Compression Noise (APCN), which can be tuned in real-time to allow users to adjust radar performance depending on their surroundings. Research scientist, Mark Govoni explained: 'Having the ability to transmit a radar waveform that's continually changing, one that never repeats itself, and looks like noise, is extremely difficult to intercept....and remains anonymous to radar detectors.'
It's not just frequency hopping.
Radars have a pattern called Staggered PRF Frame, which is a repeating pattern. and this, along with frequency, pulse width and PRI is used to identify a radar.
We already have frequency agile radars. We can identify them because the other characteristics are still constant.
If you make the frame look like random noise then it just looks like clutter. VERY hard to spot.
This is important because you don't just waste HARMs firing at random clutter, and you certainly don't want to accidentally fire on an unexpected friendly.
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If a spread spectrum signal is below the noise floor, there's no way of telling that it's even there unless you know the pattern.
Even signals below the noise are detectable since any signal will raise the noise level somewhat. So if the noise level is higher at a specific direction for no natural reason occams razor would give that it's something there. And since it's now known that a radar technology exists with this kind of pattern it is detectable. It may take some time to detect it, but it's not impossible.
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