Low Probability of Intercept (LPI) Radars

The Low Probability of Intercept (LPI) capability of the radar defeats conventional RWR/ESM systems,

each LPI pulse has considerably less amount of energy and may not fit normal modulation patterns, the target will have a difficult time detecting the aircraft" F-22 as example with AN/APG-77 radar "

I knew there are several steps for countering LPI,but for what level these steps had reached..?

Can LPI- AESA be effectively jammed ?

Open discussion.  

I couldn't answer you exactly here, because I'm now behind the time. I'm now some years out of military and I never worked with digital PESA or AESA radar, only with analogue mechanical one generation from eighties. But I think some things are the same.

You have to know, that radar signal, which go from emitter become weaker, before it reach target and than signal, which go back from target to receiver again become weaker. Ergo, if RWR detector is the same sensitive as is radar receiver, than could detect radar emissions in twice of radar range. It only depend in which frequencies it listen. The jammer is most effective, when its emitting in the same frequency is stronger, than signal, which radar send and come back from target. As I hear in past it was a big problem with OSA (SAM-8 ), that it was actually unjammable, because it have so high power radar, that jammers on planes could not overcome with noise the power of returning signal. But it need very skilled operators, who know to look in crude radar picture.

AESA and PESA radars have lower power signals, so old RWR detectors could not register them and ignore hem as noise. But newer RWR detectors sensitivities could be suited for those radars. Jammers could easily overcome with power of noise the power of returning signal, but AESA and PESA radars could easier change frequencies with frequency hoping, so the jamming noise is not in the proper frequency as returning signal and radar then easily ignore jamming noise in wrong frequency and see target. But in peace time all radars work only in peace time frequency without hoping. But I think modern radars with modern digital computers could quite effectively do with jamming in constant frequency with coding signals.

To be able to "detect" the "LPI" signal, some alogarithm has been developed , allowing extraction of signal parameters and demodulation of the signal , they're Wigner-Ville Distribution and Choi-Williams Distribution .

As for the hardware , today's digital receiver has been developed hmm in a level that allow Direct sampling of the RF signal and convert it to digital output.. which later analyzed and de-modulated.

There's a limit however in sampling rate that can be conducted ..but then i think it can be overcomed in the future .

by havok

Here is a Master Thesis about LPI Radar!

DETECTION AND JAMMING LOW PROBABILITY OF INTERCEPT (LPI) RADARS by Aytug Denk

It's very scientific, but it's worth to read it. Be warned around 120 pages!

It's like marcellogo wrote! The signal from LPI radar is still there, but it's difficult to filter the correct signal. LPI radar splits the power over broader wavelength, so at some point the signal merge with background noise and it's difficult to detect. LPI radar user will face the same problem, because the detection distance is really low in LPI mode! So you need fast computer power to bring all variables together to unmask a LPI radar.

Ah and by the way...
To make a radar more and more powerful is not good for the LPI mode, ok you can split the power over a broader wavelength, but the trick of the LPI mode is less power to be not detected! LPI radars can work in both modes conventional or in LPI mode. The videos, factsheet whatever of Murica stealth fanboys are mostly bullshit.

Azi wrote:Here is a Master Thesis about LPI Radar!

DETECTION AND JAMMING LOW PROBABILITY OF INTERCEPT (LPI) RADARS by Aytug Denk

It's very scientific, but it's worth to read it. Be warned around 120 pages!

It's like marcellogo wrote! The signal from LPI radar is still there, but it's difficult to filter the correct signal. LPI radar splits the power over broader wavelength, so at some point the signal merge with background noise and it's difficult to detect. LPI radar user will face the same problem, because the detection distance is really low in LPI mode! So you need fast computer power to bring all variables together to unmask a LPI radar.

Ah and by the way...
To make a radar more and more powerful is not good for the LPI mode, ok you can split the power over a broader wavelength, but the trick of the LPI mode is less power to be not detected! LPI radars can work in both modes conventional or in LPI mode. The videos, factsheet whatever of Murica stealth fanboys are mostly bullshit.

So you need the capacity of am Iphone 5 to found the LPI radar.

Say if the radar using 500 MHz to jump between frequencies then you need a cpu that can process 500-1000 MByte per sec, to find the radar signal and follow it.

it is easy to found small universal cpus from phones that can do 1-15 128 bit instruction on each byte of this data,and custom IC can do one magnitude more.

Of course an old, non SDR receiver can not find the transmitter.
But we are not in the stone age any more.