Almaz S-300: China's "Offensive" Air Defense

Are you referring to Frequency Modulated Continuous Wave illumination with FMCW? That is in no way has any connection with LPI. "Chirping" on CW should rather be a common technique in order to improve signal gain on CWI and it is a necessary part of CW in order to get range data in the same way you need the pulses for pulse radar. A seeker or fire control radar that uses CW should be using FM in order to get range data and improve signal gain and there is no need to advertise a common feature. Even though some people would like to class CW itself as some sort of LPI radar, its not, since CW is the most common basis for missile fire control illumination and has long been factored into RWRs long ago, as well as any range gathering method used herewith.



"Frequency modulated continuous wave (FMCW) radar is most com-
monly used to measure range R and range (radial) velocity of a target
[42, 43]."



"Range and velocity are detected through pulse delay ranging and the Doppler effect (pulse-Doppler), or through the frequency modulated continuous wave (FMCW) technique and range differentiation. "

Sorry, you are again using material as evidence without quite understanding what they mean. Nowhere does your evidence say that FMCW is commonly used. And the evidence you produce also clearly undermines your position. The problem is that you have severe misunderstandings about CW and its common usage. CW is commonly used for missile guidance, not FMCW. The quote you give "Frequency modulated continuous wave (FMCW) radar is most commonly used to measure range R and range (radial) velocity of a target[42, 43]." can cause a little misunderstanding to the less familiar, but what he probably means is that it's a common use of FMCW, not that FMCW is in common use. That's because the majority of radars measure range by sending radar pulses and measuring the time it takes to return. This is elementary, I'm surprised you'd need me to explain this? Now back to your source, notice here.

"CW radars have a very big advantage — very low peak power. As
the transmitted power can be below 1 W (many of them work with 1
mW power), they belong to the low probability of intercept (LPI) class
of radars, which can detect targets while they remain undetected."

Like I said, FMCW allows for low peak power, which is the parameter which determines ESM detection range. Reducing peak power is an established method to lower probablity of interception. Radar detection range depends on average power, which the FMCW maximises because it is a continuous wave (energy spread out over time). That is how it achieves such a low peak power which normal radars cannot achieve.

Em no. FMCW is also used in missile guidance, and especially in missile guidance even if you don't need range data. Simply said FMCW allows for better signal gain than pure CW, and that is essential for the tiny arrays in missile seekers. That alone would have justified the use of FMCW or "chirping" CW. And again, how would you know if the missile does not need range data. You cannot discount that the ground radars that would illuminate the targets would not need range data?

When something stops being an effective LPI---RWRs know all the forms of CW---is when the reciever knows what to look for. FMCW does not improve low probability of interception because it basically adds timed and spaced chirps (sawtooth shaped peaks of high power) into the CW waveform. These spaced peaks in effect, act like pulses that can be used to obtain range data. Anytime you add peaks, you are increasing probability of intercept. FMCW itself is an old and common technology and it has many civilian applications.

I'm sorry, but you are demonstrating quite clearly you have no idea what is it you are talking about. I do not know of any missile guidance which uses FMCW, though I do not discount the possibility that there are some which might use it. However, the vast majority uses CW and not FMCW, like the SARH Sparrow II, the ESSM etc.

You cannot discount that the ground radars that would illuminate the targets would not need range data?

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They get range by using the phase modulation technique, not frequency modulation as in FMCW. The search or target designation radar is not the one which uses CW, it is the target illumination radar, if SARH guidance is used.

When something stops being an effective LPI---RWRs know all the forms of CW---is when the reciever knows what to look for. FMCW does not improve low probability of interception because it basically adds timed and spaced chirps (sawtooth shaped peaks of high power) into the CW waveform. These spaced peaks in effect, act like pulses that can be used to obtain range data. Anytime you add peaks, you are increasing probability of intercept.

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I'm sorry, your basics here is so far gone I truly don't know where to start. I can only try to correct some parts but the basics you'll have to really pick up a textbook to understand. Chirps are not 'peaks', (whatever you mean by 'peaks'), they are signal changes in freq over time. It is not 'peaks' but peak power transmitted that is what ESMs utilise for detection. FMCW allows for reduction in peak power transmitted while still maintaining (as best as possible) average power transmitted. That's why FMCW radars like Scout can have low peak power outputs on the order of 1Q or below. Average power transmitted is the parameter which determines radar detection performance. To make it simpler for you to understand, what FMCW accomplishes is to make the transmitted peak signal so weak the ESM cannot pick it up. If peak power reduction doesn't constitute a legitimate LPI technique in your eyes, I don't know what can. I do know that radar engineers agree with me on this though.

FMCW itself is an old and common technology and it has many civilian applications.

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Certainly there's nothing mystical about it. But the drawbacks and the difficulties in obtaining range have limited its military use to specific niches.

So far I think I have repeated myself 3 times, so I will end it here. I guess it is up to you whether you wish to take my advice or not, but I certainly hope people here haven't been mislead.

Kongo said:

I'm sorry, but you are demonstrating quite clearly you have no idea what is it you are talking about. I do not know of any missile guidance which uses FMCW, though I do not discount the possibility that there are some which might use it. However, the vast majority uses CW and not FMCW, like the SARH Sparrow II, the ESSM etc.

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From what I know, the Nike Hercules, the S-200, uses it, as well as most SAM radars, which by the way, do need range information on the tracking unit. Often the term is Interrupted CWI. Aircraft radar also uses, starting from the earliest sets of the F-14 and the F-15.

ESSM uses it under the term Interrupted CWI.



Another system that uses it.



So does the Standards.



Aircraft system that uses it.



The term FMCW, FMICW or just ICW is used interchangeably but mean the same thing.

They get range by using the phase modulation technique, not frequency modulation as in FMCW. The search or target designation radar is not the one which uses CW, it is the target illumination radar, if SARH guidance is used.

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How so? Phase modulation isn't as widely used.

I'm sorry, your basics here is so far gone I truly don't know where to start. I can only try to correct some parts but the basics you'll have to really pick up a textbook to understand. Chirps are not 'peaks', (whatever you mean by 'peaks'), they are signal changes in freq over time. It is not 'peaks' but peak power transmitted that is what ESMs utilise for detection.

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They are frequency changes over time to be exact. Like sudden increases in frequency and these bursts of short frequency create compressed pulses. FMCW does not offer any decrease in terms of peak power over CW.

FMCW allows for reduction in peak power transmitted while still maintaining (as best as possible) average power transmitted. That's why FMCW radars like Scout can have low peak power outputs on the order of 1Q or below. Average power transmitted is the parameter which determines radar detection performance. To make it simpler for you to understand, what FMCW accomplishes is to make the transmitted peak signal so weak the ESM cannot pick it up. If peak power reduction doesn't constitute a legitimate LPI technique in your eyes, I don't know what can. I do know that radar engineers agree with me on this though.

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Excuse me but FMCW is used in a much broader term. It just seems to me that you just discovered FMCW newly with the context of LPI, when in fact, FMCW has been around nearly as long as CW is around, which was before Pulse Doppler. FMCW is simply, a way of getting range for CW.



FMCW can be used for LPI yes, but not all FMCW radars are intended to be LPI.

Scout uses FMCW not primarily as an LPI form, though the bonus is convenient, but for use as short range radars, FMCW does not have a minimum range like pulse doppler, gets less ambiguities, it works better at short range, resistant to ground clutter and therefore better to detect and track low flying objects. That's precisely why its used (in different terminologies) in most SAM systems.

Sorry, as I said, I'd rather not repeat myself further.

Look here page 1057. You decide if FMCW and ICW is the same.


Do read up more on the Scout, and decide for yourself what is the specific feature they use to achieve it's LPI nature.

Actually ICW and FMCW is very close, because both makes changes within the continuous wave through frequency changes and all are modulated CW and modulated CW is mainly for getting range data for CW. All my examples show the use of modulated CW that points to the missile also using range data as well as any improvements in signal gain. You are only showing the differences in wave forms. Look at the text again, and there is nothing there that says that one modulation technique is more LPI than the other. CW being low power comes from its property of being a continuous wave and not because of modulation properties. Stop making ads the foundation of physics.

Read again the text I posted from the PDF of that engineer. He talks about hypothetical ESM receiver which for the purposes of discussion is able to detect modulated CW emitters.

"The MIR forms a useful generic starting
point for the analysis of future ESM
capabilities because it does not require a
detailed knowledge of the receiver
architectures, but can treat them at a more
general level. For example, it is shown in
reference 1 that the MIR provides a good
estimate of the best-case sensitivity which a
scanning superhet. can achieve against an
agile modulated-CW emitter.
The sensitivity of the MIR is approximately
(2BRFBV), so for a radar with 100MHz
bandwidth and 4ms dwell time (a
bandwidth of 125Hz), the effective
bandwidth is about 160kHz, compared with
2GHz for the IFM-based receiver discussed
in table, and is indicative of the practical
limits of sensitivity of the intercept
receiver."

Then using this hypothetical receiver, he goes to to describe how far this receiver can detect the "baseline' radar, aka Pilot/Scout.

"This is about 20dB better than a current
“state of the art” channelized receiver and
would allow the free-space interception
range to be increased to 280km against the
main beam of the “baseline” radar whose
parameters are shown in table 1,"

So the radar that can only be detected from 25km using a baseline late 80's ESM receiver can now be detected at 280km using his hypothetical Matched Incoherent Receiver.

Here is where you don't *understand* the relationships of sidelobes.

"but the range against sidelobes 40dB below the
main beam would still be only 2.5km."

Meaning, even if you have the new receiver that can defeat the agile modulated CWI, there is no change in the detectability through its sidelobes.

"and the range would only be 8km if the
transmitter power could be reduced to
1mW. "

Which of course, he's talking only about the main lobe.

So even the main lobe at minimum power transmission still has a longer detect range than the side lobe of the radar operating at full power.

In other words, what I am pointing out with low sidelobes is a separate issue from waveforms and modulation techniques.

Actually ICW and FMCW is very close, because both makes changes within the continuous wave through frequency changes and all are modulated CW and modulated CW is mainly for getting range data for CW.

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No, they are fairly similar, but hardly the same, and so the terms ICW and FMCW are definitely not interchangeable as you tried to assert. Please refrain from further confusing readers.

Look at the text again, and there is nothing there that says that one modulation technique is more LPI than the other.

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Where have I said that one CW form is more LPI than the other?

CW being low power comes from its property of being a continuous wave and not because of modulation properties. Stop making ads the foundation of physics.

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I guess it is good that you finally admit FMCW is a LPI technique, but I am offended that you would try to make it sound as if I made the silly assertion that low peak power came from frequency modulation and not the signal being a continuous wave. Please point out where I have done so. If you are unable to do so, please have the decency as a moderator to apologise.

Read again the text I posted from the PDF of that engineer. He talks about hypothetical ESM receiver which for the purposes of discussion is able to detect modulated CW emitters.

"The MIR forms a useful generic starting
point for the analysis of future ESM
capabilities because it does not require a
detailed knowledge of the receiver
architectures, but can treat them at a more
general level. For example, it is shown in
reference 1 that the MIR provides a good
estimate of the best-case sensitivity which a
scanning superhet. can achieve against an
agile modulated-CW emitter.
The sensitivity of the MIR is approximately
(2BRFBV), so for a radar with 100MHz
bandwidth and 4ms dwell time (a
bandwidth of 125Hz), the effective
bandwidth is about 160kHz, compared with
2GHz for the IFM-based receiver discussed
in table, and is indicative of the practical
limits of sensitivity of the intercept
receiver."

Then using this hypothetical receiver, he goes to to describe how far this receiver can detect the "baseline' radar, aka Pilot/Scout.

"This is about 20dB better than a current
“state of the art” channelized receiver and
would allow the free-space interception
range to be increased to 280km against the
main beam of the “baseline” radar whose
parameters are shown in table 1,"

So the radar that can only be detected from 25km using a baseline late 80's ESM receiver can now be detected at 280km using his hypothetical Matched Incoherent Receiver.

Here is where you don't *understand* the relationships of sidelobes.

"but the range against sidelobes 40dB below the
main beam would still be only 2.5km."

Meaning, even if you have the new receiver that can defeat the agile modulated CWI, there is no change in the detectability through its sidelobes.

"and the range would only be 8km if the
transmitter power could be reduced to
1mW. "

Which of course, he's talking only about the main lobe.

So even the main lobe at minimum power transmission still has a longer detect range than the side lobe of the radar operating at full power.

In other words, what I am pointing out with low sidelobes is a separate issue from waveforms and modulation techniques.

Click to expand...

We have established that the use of FMCW is a fairly unique case among radars. Since the ability to pick up sidelobe emission is dependent on how much power is radiated from the sidelobes, and radars which use FMCW waveforms emit very low peak powers because of that, then it is not reasonable to use an example based on FMCW based radar to back up your position.

While I agree that sidelobe emissions are harder to pick up from new AESA designs, I don't really see that as an big impediment as far as the US is concerned. Sidelobes are reduced, but they are not eliminated. There are ways round the problem of trying to detect low sidelobes. To think that none exist would show that one's awareness of the state of the art is lacking.

Kongo said:

No, they are fairly similar, but hardly the same, and so the terms ICW and FMCW are definitely not interchangeable as you tried to assert. Please refrain from further confusing readers.

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They are for the same practical purpose, try to do the same thing, which is to break up the continuous wave into distinguishable segments.

Where have I said that one CW form is more LPI than the other?

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You seem to clearly imply it that for some reason, FMCW is more LPI than phase modulation or interrupted CW.

I guess it is good that you finally admit FMCW is a LPI technique, but I am offended that you would try to make it sound as if I made the silly assertion that low peak power came from frequency modulation and not the signal being a continuous wave. Please point out where I have done so. If you are unable to do so, please have the decency as a moderator to apologise.

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No. Don't put words into my mouth please. I never implied FMCW is an LPI technique. I clearly stated its nothing more than a modulation form for CW radars used to get ranged data.

We have established that the use of FMCW is a fairly unique case among radars.

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No you have not established that. Read the links I showed you again. It says its the most commonly used form of modulation used to obtain ranged data for CW. Pick up a dictionary and find out the meaning of the word "common". This is not to mention the many commercial forms of this radar. Just google it.

Since the ability to pick up sidelobe emission is dependent on how much power is radiated from the sidelobes, and radars which use FMCW waveforms emit very low peak powers because of that, then it is not reasonable to use an example based on FMCW based radar to back up your position.

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SIGH.

Read the text again. You don't seem to understand ANY OF THIS right from the beginning.

The PDF described a receiver that could pick up agile CW systems, so that the detection range against the system is now at 280km. And yet there is no change in the detectability from the sidelobes.

Do note that emitting low power is not a characteristic, its an option. You can read from the text that the example of the baseline radar wasn't operating at low, and its only at the bottom of the text that its set to low, with a detectability of the main lobe at 8km. The catch with using low power, which is why its an option, not a characteristic, is that don't expect to detect low RCS objects with it. For the FMCW system, and no different from any modulated CW system, to detect and track low RCS objects, your power has to go high.

While I agree that sidelobe emissions are harder to pick up from new AESA designs, I don't really see that as an big impediment as far as the US is concerned. Sidelobes are reduced, but they are not eliminated. There are ways round the problem of trying to detect low sidelobes. To think that none exist would show that one's awareness of the state of the art is lacking.

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Of course, this is already understood. What it only shows that this is now a matter of greys and uncertainty, not black or white or certain superiority that some people like to show.

Please do note that to be an ULSA, the strength of the sidelobe is one tenth to the thousandth of the main lobe.

They are for the same practical purpose, try to do the same thing, which is to break up the continuous wave into distinguishable segments.

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All radars have the same practical purpose, but just because they do doesn't make them intechangeable. It's surprising that you'd still try to spin your way out of this one, but I guess as a mod you are free to do as you wish. Feel free to everlook the differences which make them 2 similar but distinct waveforms.

You seem to clearly imply it that for some reason, FMCW is more LPI than phase modulation or interrupted CW.

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I'm disappointed in you. If you are unable to interpret clearly what I say because you are not well versed enough, that is not my fault. Please don't accuse me of saying things I didn't, and ridiculing me based on that. It's offensive.

No. Don't put words into my mouth please. I never implied FMCW is an LPI technique. I clearly stated its nothing more than a modulation form for CW radars used to get ranged data.

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It's quite hard to fathom that you'd actually acknowlege FMCW decreases peak power but deny that it's a LPI technique, despite many texts on LPI radars listing it as one. Perhaps what's stopping you from admiting it is because you have claimed outright earlier that FMCW is not a LPI technique?

No you have not established that. Read the links I showed you again. It says its the most commonly used form of modulation used to obtain ranged data for CW. Pick up a dictionary and find out the meaning of the word "common". This is not to mention the many commercial forms of this radar. Just google it.

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Again, goes to show how much you do not know. Try picking up Jane's Radar and electronic systems or some other radar textbooks. Most search radars are pulse doppler radars. Those radars which use uninterrupted continuous waves are comparatively fewer, and FMCW is only common among those which have ranging as a function. Which in the end means that FMCW radars are very few, limited to Scout, Pilot, Page and a few others.

SIGH.

Read the text again. You don't seem to understand ANY OF THIS right from the beginning.

The PDF described a receiver that could pick up agile CW systems, so that the detection range against the system is now at 280km. And yet there is no change in the detectability from the sidelobes.

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Detection range increases exponentially with increases in power transmitted. Because the FMCW radar's sidelobes are so low, this is at the very low end of the curve, hence the increase in ESM sensitivity isn't enough to compensate. In pulse doppler radars which form the majority of military radars however, to achieve the same range would require a much higher peak power output and a correspondingly higher sidelobe power output. Which is why FMCW radars are not a good example to prove your point. The paper AG Stove you brought out as 'evidence' is only an abstract. In a much more comprehensive paper which he, AL Hume and CJ Baker co-authored titled "Low probability of intercept radar strategies", it was clearly stated that "any free-space detection range is possible, given a sufficiently sensitive receiver." Even with lower sensitivity receivers, detection range can be increased with tradeoffs in detection time and detection probabilities. That is clearly shown in the paper, whereby using a dish antenna as opposed to a wide-beam antenna allows for an increase in sidelobe detection range from 2 to 50km at a cost of 1.7s in detection time and a decrease of 10% in terms of probability of intercept.

Do note that emitting low power is not a characteristic, its an option.

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Sure, emit nothing and you will be undetectable by any intercept receiver. Any fool knows that. What FMCW offers is much lower average power required than pulse doppler radars to achieve the ranges against a target (assuming all other factors remain equal) it can. That, you don't know.