Following a long discussion on the relative ranges of fighter radars and RWRs in long-range engagements in the ‘Dassault Rafale #14 – News & Discussion’ thread, a forum member rightly suggested that this discussion was off-topic and should be moved to its own thread. Several other members then expressed an interest in having a dedicated EW thread,, so I promised to start one after I had completed some urgent work and a long-delayed computer rebuild over the Easter break.
Both tasks are now finally completed (my expectation that reinstalling and configuring all my software could be done in three to four days proved somewhat inaccurate!), so here is the promised thread.
The first subject must be to finish the radar v. RWR discussion.
As they used to say in the old B&W cinema serials that I enjoyed as a kid…
THE STORY SO FAR…
(This will spare people from the task of flipping back to the earlier thread.)
This whole thing started in the ‘Dassault Rafale #14 – News & Discussion’ thread when a possible long-range Rafale versus Su-35 engagement was discussed, including the use of both active radar and the exploitation of threat data for an RWR.
Kovey wrote in posting 590:
“What is extremly simplistic is ignoring the fact that a EW system will detect your radar emission 2 times further away than your radar effective range,”
Hopsalot disagreed in posting 621, saying “My primary point is that it is not a given that a RWR will always detect a radar before the radar is able to track its target. That may be the more common outcome, but it is not a given.”
In his posting 626, BlueApple argued that at long range, the detection range of an RWR would greatly exceed that of an active radar, and some potential values of signal levels to show what he meant.
Reponding in posting 637, Hopsalot suggested conditions in which a radar might detect its target before the RWR detects the radar.
”Yes the RWR has some substantial advantages if you limit yourself to a superficial look at the equations, but the radar also possesses significant advantages and in actual practice it is not a given that a RWR will detect the radar first. Even in situations where the RWR does detect the radar first, it may not do so at an appreciably greater range than the radar is capable of tracking its target.”
My posting 645 referred back to Blue Apple’s discussion of signal levels in a long-range engagement:
“Although real-world signal levels may be a bit different from his ballpark figures, the underlying balance remains the same. At long ranges, the RWR will always win.”
As evidence for the RWR’s advantage at most tactical ranges, in posting 658, I cited two passages from the Third edition (published in 2008) of Merrill Skolnick’s ‘Radar Handbook’ – one of the basic reference texts for the radar engineer.
“Range advantage due to one-way propagation with respect to two-way propagation allows radar interception at farther range than own platform detection.”
And…
“It is noted that the RWR detection performance is inversely proportional to [R squared] rather than to [R to the power 4] of the radar target detection equation. For this reason, the RWR can detect a radiating radar at distances far beyond those of radar’s own target detection capability.”
Hopsalot responded in posting 659
“You claimed that based on the math/physics the RWR always had an insurmountable advantage. I showed you that that was not the case.”
In practice, I had not made such a claim. That “always had” seems to be his invention. In my posting 673 quoted above, I specifically stated that the RWR’s advantage was at long range. And long range was what we were talking about – a hypothetical engagement between a Rafale and an Su-35.
I challenged Hopsalot to produce evidence to back up his opinions, and in posting 622 he linked to three documents:
http://www.dtic.mil/dtic/tr/fulltext/u2/a246315.pdf
http://www.saabgroup.com/Global/Docu…NG%20print.pdf
http://ieeetmc.net/r5/dallas/aes/IEE…ov04-Wiley.pdf
And that summary of the saga brings us up to date.
So what do Hopalot’s links say? Do they document conditions in which a radar-equipped fighter will see an enemy fighter and that enemy fighter’s RWR will not see the radar?
Alas, they do not.
The first paper cited was a 1991 paper “Interception of LPI radar signals” by Jim Lee of the Defence Research Establishment, Ottawa.
Page 11 of this document sets out what is being discussed.
“The case of a LPI radar versus EW receivers is illustrated by considering three functions of a radar in the areas of (a) search (b) ASM RF seeker and (c) navigation.
The three different types of EW intercept receivers as discussed in Sections 2.2.1 to 2.2.3 are assumed to be operating on a shipborne platform.”
This is talking about naval warfare, and is a long way from the world of air-to-air combat!
Page 23 of Lee’s paper cited an example of an LPI radar:
“Philips in Sweden and Signaal in the Netherlands have developed the “quiet” navigation radars PILOT and SCOUT for covert operations…PILOT uses a frequency modulated continuous wave (FMCW) transmitter with low peak power (typically 1 Watt).”
One watt of power may be adequate very when you are mapping terrain and located surface ships with radar cross sections in the order of 5,000 – 100,000 sq m a few tens of kilometres distant, but what was originally being discussed was an enemy fighter (with an RCS in the 10 sq m class or less) at long range.
Page 43 of Lee’s paper talks about the limitations of LPI radars:
“It has been shown that LPI operation is most easily achieved at close ranges only. In the search function, the range is usually quite large and the target size can be small. As a result, it is very difficult to design a radar LPI against conventional EW receivers when the mainbeam is intercepted.”
And that last sentence sums up the problem. In a fighter versus fighter engagement, the fighter that opts to use radar will be sweeping its main beam though a volume of space in order to try to locate its target. Intercepted energy from that main beam will betray the radar’s presence to an enemy RWR.
On page 44, Lee goes on to discuss possible ESM receiver configurations that have been examined “in this report for shipborne applications”, and notes that these have “shown some promise in terms of providing the sensitivity and capability in an environment where both conventional and LPI signals are present.”
So “some promise” of anti-LPI capability was already available two decades ago, when Lee’s paper was written.
The second document cited was a leaflet for the Saab PILOT – a short-range LPI shipboard navigation radar mentioned in Lee’s paper.
The third document is an undated presentation on “The Future of EW and Modern Radar Signals” by Richard G. Wiley from Research Associates of Syracuse, a well-known maker of elint and ESM systems.
One slide titled “Deployed LPI Radars (Last updated in 1998)” lists:
Scout: over 130 deployed (per MSSC)
Squire: Development being completed.
Page: Production expected in 2002 (MSSC)
Pilot: less than 50 deployed (CelsiusTech)
Hard: (Ericsson)
MICOM: Laboratory only
FGAN: OLPI, Laboratory only
I have details of several of these radars. All are short-range systems.
HARD is an X-band early-warning radar with a range of about 15 km against a fighter-sized target. But even this level of performance required 65 W of peak RF power compared with the 1 w quoted for PILOT.
Squire is a J-band ground-surveillance radar with up to 1 W of power, and the ability to track boats and heavy vehicles out to 24 km or helicopters at 14 km.
Page is a portable air-surveillance radar with a 20 W output and a maximum range of 20 km.
Another slide in Wiley’s presentation is titled “Example for Existing Designs” and cited the following conditions as an example of radar versus ESM.
• RCS =1 sq meter
• Rx Ant Gain =1, Sidelobe Tx Ant. Gain=1
• ESM Rx 20 dB less sensitive than Radar Rx
• Then the Sidelobes of the Radar can be detected at a range of over 30 times the range at which the radar can detect a target
• Main beam detection over 1000 times Radar Range
Given who his employers are, I think we can assume that Mr Wiley knows what he is talking about when he cites such ranges for main-beam and sidelobe detection.
Sign In
April 6, 2013 at 3:09 pm