Countermeasure against anti raditation misslie

[Grand Danois]

Pulled this from the (in)famous Wikipedia. May provide some further input.

Low probability of intercept

A low probabililty of intercept radar (LPIR) is designed to be difficult to detect by passive radar detection equipment (such as a radar warning receiver - RWR) while it is searching for or tracking a target. This characteristic is desirable because it allows finding and tracking an opponent without alerting them to the radar's presence.

Ways of reducing the profile of a radar include using wider frequency bandwidth (wideband), frequency hopping, using a frequency-modulated continuous-wave signal, and using only the minimum power required for the task. Using pulse compression also reduces the probability of detection, since the peak transmitted power is lower while the range and resolution is the same.

Constructing a radar so as to emit minimal side and back lobes may also reduce the probability of interception when it is not pointing at the radar warning receiver. However, when the radar is sweeping a large volume of space for targets, it is likely that the main lobe will repeatedly be pointing at the RWR. Modern phased array radars not only control their side lobes, they also use very thin, fast moving beams of energy in complicated search patterns. This technique may be enough to confuse the RWR so it does not recognize the radar as a threat, even if the signal itself is detected. All military EM emitters, including fighter aircraft, naval ships, and missile systems are designed for reduced electromagnetic profiles for improved stealth.

In addition to stealth considerations, reducing side and back lobes is desirable as it makes the radar more difficult to characterise. This can increase the difficulty in determining which type it is (concealing information about the carrying platform) and make it much harder to jam.

Systems which feature LPI include modern AESA radars such as that on the F/A-18E/F Super Hornet and the electronically steered phased array on the S-300PMU-2.

Thales Defence Deutschland GmbH in Kiel has designed a LPI radar system for naval vessels which operates in combination with a pulse radar. For open operation the vessel is running the pulse radar. The boat will be identified by ESM systems (fingerprint of boat). For secret missions it is switched to LPI radar. It works in FMCW mode with min. 1mW in 24 NM .The boat remains invisible for ESM systems. The so called SPHINX radar systems is supported by a pressuretight Microstrip Antenna MSA with CsC feature for simutianously sea&air observation. References: Greece Navy, South Korean Navy

http://en.wikipedia.org/wiki/Low_probability_of_intercept

 

[Totoro]

I don't think LPI is so much a function of the radar array as it is of the software (and hardware to go with it) that governs that radar. Yes, phased arrays do offer some unique qualities - like the mentioned small side lobes and fast scanning (that's applicable for both PESA and AESA) but ultimately it comes down to software. It is a guaranteed thing that today's/tomorrow's RWRs will be tested on various kinds of arrays, and 'trained' to recognize patterns unique to phased arrays, like very fast scanning, just like older RWRs were designed t recognize different patterns, typical for mechanical radars. Given the same level of technology on both sides, i don't see how there can be a true stealth radar with undetectable emissions.

 

[crobato]

I agree. The thing about LPI is that it assumes that the radar designer knows very well how RWRs work, and I mean RWRs that are already a known quantity, or whose detection algorthyms you are familiar with. Usually the same country as the one that makes the LPI radar itself.

The thing is, you don't really know what is going on inside another country's RWR, or what its algorhythms are. You are basically reduced to a set of assumptions, which won't be tested directly until you are in the heat of battle.

The analogy is like knowing the map of a minefield. If you know where the trip points are, you can avoid it. But if the map is unknown, its a whole different ballgame. You are reduced to assumptions, and "cross your fingers hope it will work".

 

[Ozzy Blizzard]

Thats a dangerous assumption for LO aircraft like the F22. What if the enemy's RWR has picked them up and they think their undetected, could get a nasty suprise. all the stealth in the world wont help you if they can see your radar.

 

[crobato]

LPI works when the other guy thinks you're not using it but you actually are. The worst thing to happen is to blab about it in public in an attempt to market an arrogant sense of technical superiority. But now that everyone knows you're going to use LPI techniques, the next generation of RWRs are going to be clued to look for LPI signals, while current ones are going to have have their detection algorthyms updated.