Chinese Radar Developments - KLJ series and others

Jason_ said:

In most cases, the ability to sustain high power radar operation is limited by cooling not power generation. The fact that the J-10C radar is liquid cooled and housed in a redesigned forward fuselage implies that it should compare very favorably to the retrofitted AESAs on the Rafale or the F-16.

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Yeah this is good. Liquid cooling does indeed provide more cooling capacity than air cooled which limited to about 2-3 KW/sqm of antenna aperture. Rafale AESA however is also liquid cooled. The liquid cooling performance in other hand would be limited typically by the amount of fuel the aircraft can carry as that's the medium where the coolant solution will dump the heat.

Thus more fuel = more cooling potential.

In the other hand, air cooling is easier to implement, light and may have little impact to the aircraft's structure, thus why those AESA upgrades for legacy fighters are typically air cooled.

However the main driver of AESA performance would be number of TRM's as the performance gain, scales by cube of TRM. Radar that can pack more TRM's than the other will usually "win" in terms of performance. Radar with less number of TRM's when trying to match the performance of the radar with more TRM's will be "penalized" in cooling and power requirement and thus cost.

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Trying to compare J-10 AESA's with "other kids in the block" could start with comparing number of TRM's. Let's say, from a twitter poster i got 1200 TRM's for J-10B AESA, how does that compare to say an APG-79 with 1368. One can then use the 4th root law with cube of the TRM's. Using APG-79 as base.

Rfac=((1200/1368)^3)^(1/4)
Rfac=0.906

Basically the range of the J-10 AESA is 10% shorter than the APG-79. How about comparing with AN/APG-80 with 1020 TRM ? same method.

Rfac=((1200/1020)^3)^(1/4)
Rfac=1.13

Thus the J-10 AESA would have 13% range advantage over APG-80.

and how about Rafale ? It has TRM count of 838 according to photo although you will see people claiming 1000 TRM. If we stick to the google image it would be :

Rfac=((1200/838)^3)^(1/4)
Rfac=1.3

The 1200 TRM AESA will have 30% advantage in range. But hey how about element power ? Same methods. Let's say the French put TRM twice the power of the J-10's or a factor of 0.5 against the J-10.

Rfac=((1200/838)^3*(1/2))^(1/4)
Rfac=1.1

The French radar gained 20% (should be closer to 19% however) range but radar with larger amount of TRM still wins. In order to match or maybe reverse the gain from having more TRM's. The TRM power would need to be increased by factor of at least 3. This however will have direct impact on cooling, power requirement and cost of the TRM's.

Stealthflanker said:

Yeah this is good. Liquid cooling does indeed provide more cooling capacity than air cooled which limited to about 2-3 KW/sqm of antenna aperture. Rafale AESA however is also liquid cooled. The liquid cooling performance in other hand would be limited typically by the amount of fuel the aircraft can carry as that's the medium where the coolant solution will dump the heat.

Thus more fuel = more cooling potential.

In the other hand, air cooling is easier to implement, light and may have little impact to the aircraft's structure, thus why those AESA upgrades for legacy fighters are typically air cooled.

However the main driver of AESA performance would be number of TRM's as the performance gain, scales by cube of TRM. Radar that can pack more TRM's than the other will usually "win" in terms of performance. Radar with less number of TRM's when trying to match the performance of the radar with more TRM's will be "penalized" in cooling and power requirement and thus cost.

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Trying to compare J-10 AESA's with "other kids in the block" could start with comparing number of TRM's. Let's say, from a twitter poster i got 1200 TRM's for J-10B AESA, how does that compare to say an APG-79 with 1368. One can then use the 4th root law with cube of the TRM's. Using APG-79 as base.

Rfac=((1200/1368)^3)^(1/4)
Rfac=0.906

Basically the range of the J-10 AESA is 10% shorter than the APG-79. How about comparing with AN/APG-80 with 1020 TRM ? same method.

Rfac=((1200/1020)^3)^(1/4)
Rfac=1.13

Thus the J-10 AESA would have 13% range advantage over APG-80.

and how about Rafale ? It has TRM count of 838 according to photo although you will see people claiming 1000 TRM. If we stick to the google image it would be :

Rfac=((1200/838)^3)^(1/4)
Rfac=1.3

The 1200 TRM AESA will have 30% advantage in range. But hey how about element power ? Same methods. Let's say the French put TRM twice the power of the J-10's or a factor of 0.5 against the J-10.

Rfac=((1200/838)^3*(1/2))^(1/4)
Rfac=1.1

The French radar gained 20% (should be closer to 19% however) range but radar with larger amount of TRM still wins. In order to match or maybe reverse the gain from having more TRM's. The TRM power would need to be increased by factor of at least 3. This however will have direct impact on cooling, power requirement and cost of the TRM's.

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Not as simple as number of elements. Transmit power of each of the individual element matters too.

latenlazy said:

Not as simple as number of elements. Transmit power of each of the individual element matters too.

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Yes and as you see i took it into account too for the last part of my post where i said to match the advantage of 1200 TRM radar, the smaller 838 Rafale radar must have 3 times increase in power. So the rules of thumb would look as follows :

Rfac = ((Nx/Nref)^3*(Px/Pref))^(1/4)

Where the Px is your target/scaled radar's TRM power, Nx is your target/scaled radar's TRM number while variable with "ref" in it is the reference value or baseline value. Rfac here is range factor which you can multiply with your radar's reference range

Now let's have another example of usage. Both radars have 1200 TRM, each TRM have 10 Watts of power.

Running the equations :


Rfac = ((1200/1200)^3*(10/10))^(1/4)
Rfac = 1

Both radar are identical in performance. Now we want the scaled radar's TRM to have twice the power (20 Watts) Then the equation would look like this :

Rfac = ((1200/1200)^3*(20/10))^(1/4)
Rfac = 1.19

As you see increasing the TRM power by factor of 2 only yield 19% increase in range.

How about now we increase the number of elements by factor of 2 so the scaled radar have 2400 elements.

Rfac = ((2400/1200)^3*(10/10))^(1/4)
Rfac =1.68

As seen the AESA with more TRM have 68% more range despite the power of the TRM being the same.

Stealthflanker said:

Yes and as you see i took it into account too for the last part of my post where i said to match the advantage of 1200 TRM radar, the smaller 838 Rafale radar must have 3 times increase in power. So the rules of thumb would look as follows :

Rfac = ((Nx/Nref)^3*(Px/Pref))^(1/4)

Where the Px is your target/scaled radar's TRM power, Nx is your target/scaled radar's TRM number while variable with "ref" in it is the reference value or baseline value. Rfac here is range factor which you can multiply with your radar's reference range

Now let's have another example of usage. Both radars have 1200 TRM, each TRM have 10 Watts of power.

Running the equations :


Rfac = ((1200/1200)^3*(10/10))^(1/4)
Rfac = 1

Both radar are identical in performance. Now we want the scaled radar's TRM to have twice the power (20 Watts) Then the equation would look like this :

Rfac = ((1200/1200)^3*(20/10))^(1/4)
Rfac = 1.19

As you see increasing the TRM power by factor of 2 only yield 19% increase in range.

How about now we increase the number of elements by factor of 2 so the scaled radar have 2400 elements.

Rfac = ((2400/1200)^3*(10/10))^(1/4)
Rfac =1.68

As seen the AESA with more TRM have 68% more range despite the power of the TRM being the same.

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My (very) general understanding is that for range as defined by total transmit power your number of transmitters should have the same linear relationship to total transmit as the combined power of each emitter. In other words 20% increase in number of transmitters should be equivalent to 20% increase in transmit power of the transmitters themselves.

The other thing that isn’t being factored in here is your receiver sensitivity, which is dependent on factors like electronic noise floor and receiver gain. Furthermore with AESAs my understanding is that having multiple transmitter and receiver arrays can help discriminate much fainter returns by emitting multiple or complex beams and then comparing the signal returns from different parts of the array, which means computation power and algorithmic sophistication also matter.

Overall I’m not sure these heuristics are that helpful toward determining how different AESA radars compare with one another.

latenlazy said:

My (very) general understanding is that for range as defined by total transmit power your number of transmitters should have the same linear relationship to total transmit as the power of each emitter. In other words 20% increase in number of transmitters should be equivalent to 20% increase in transmit power of the transmitters themselves.

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So you mean i cannot use the individual number of transmitter but have to "clump it" into one ? e.g 2000 TRM with 5 Watt power.. then i should input 10000 Watt in the 4th root radar reference range equation ?

latenlazy said:

The other thing that isn’t being factored in here is your receiver sensitivity, which is dependent on factors like electronic noise floor and received sensitivity.

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You can add it yourself. As long as it's in radar range equation, you can use 4th root rules on it. One exception i see so far is wavelength which can give weird result. But for noise factor, you can have it. Like mentioned in "Introduction to Airborne Radar 2nd Edition" Other exception is loss factor which on the numerator is 1.

So the equation would be something like this with noise factor :

Rfac = ((Nx/Nref)^3*(Px/Pref)*(Fref/Fx))^(1/4)

Where F is the noise factor, Different to the previous variables Since noise is in the denominator of the radar range equation. The "Scaled" factor for which the radar you wish to compare is now also in denominator while the reference factor will be the numerator. Similar thing for the SNR or Do (Detectability factor).

Now back to baseline radar with same 1200 TRM and each TRM contributes 10 Watts we compare it with another identical radar but with some technological advancement which allows reduction of noise figure by factor of 2 Thus compared to baseline Radar the noise figure of the scaled radar is 0.5, now we can put it into the equation.

Rfac = ((1200/1200)^3*(10/10)*(1/0.5))^(1/4)

Rfac = 1.19

Thus the new radar with new low noise TRM will gain the same amount of advantage as increasing transmit power twice. Then how about the radar with lesser TRM ? Can it up the one with more TRM's by say reducing the noise by factor of 2 and also increase the power by factor of 2 ? With number of TRM halved.


Rfac = ((600/1200)^3*(20/10)*(1/0.5))^(1/4)

Rfac = 0.84

So the radar still handicapped in range by 16% BUT It's much better than simply halving the number of the TRM's

Rfac =((600/1200)^3*(10/10)*(1/1))^(1/4)

Rfac = 0.59

The radar without new more powerful TRM and lower noise have over 41% shorter range compared to the radar with more TRM's. Thus lowering the noise by factor of 2 while also increase the power by 2 yield 30% improvement for the 600 TRM radar.

But do one wish to up the one with 1200 TRM ? What if we could further reduce the noise level by factor of 4 and also have say a GaN module with 4 times the one having 1200 TRM ? We can express that too.

Rfac = ((600/1200)^3*(40/10)*(1/0.25))^(1/4)

Rfac = 1.19

Hey we did it. By lowering the noise power in the TRM by factor of 4 and also increase the transmit power by 4 times or 40 Watts. Our 600 TRM radar can now have 19% longer range compared to the one with 1200 TRM baseline.

latenlazy said:

Furthermore with AESAs my understanding is that having multiple transmitter and receiver arrays can help discriminate much fainter returns by emitting multiple or complex beams and then comparing the signal returns from different parts of the array, which means computation power and algorithmic sophistication also matter.

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Regarding multiple beams tho i wonder how that is actually performed ? Particularly without messing with the Array's radiation pattern.

latenlazy said:

Overall I’m not sure these heuristics are that helpful toward determining how different radars compare with one another.

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Well i wonder why ? because if you read references the Radar Range Equation remains the same regardless of radar types. While some variables like sophistication etc may not necessarily appear or relevant in range modeling.

I believe simple 4th root rules helps mainly in determining tradeoff in Radar designs and to compare radar in more sensible manner instead of relying on buzzwords which may not necessarily relevant to the discussion or difficult to visualize. the simple 4th root rules are widely used, you can check some references like George M Siouris's Radar Performance Modelling 2nd Edition or Stimson's Introduction to Airborne Radar 2nd and 3rd Edition.

Stealthflanker said:

So you mean i cannot use the individual number of transmitter but have to "clump it" into one ? e.g 2000 TRM with 5 Watt power.. then i should input 10000 Watt in the 4th root radar reference range equation ?

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Yes…because ultimately the range is determined by total transmit power. The number of elements are just a sub component for overall transmit power. A radar with the same number of elements but with 50% lower individual element transmit power will have 50% lower total transmit power. A radar with half the elements but double the individual element transmit power will have identical total transmit power.

Stealthflanker said:

You can add it yourself. As long as it's in radar range equation, you can use 4th root rules on it. One exception i see so far is wavelength which can give weird result. But for noise factor, you can have it. Like mentioned in "Introduction to Airborne Radar 2nd Edition" Other exception is loss factor which on the numerator is 1.

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My point is not every receiver has the same receiver sensitivity or gain performance. receiver performance matters as much as transmitter performance.

Stealthflanker said:

Regarding multiple beams tho i wonder how that is actually performed ? Particularly without messing with the Array's radiation pattern.

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The point is to “mess” with the radiation patterns, but also maybe use emission strategies like time delayed pulses between different elements. This might impact total single directional transmit power of the beam but generating these complex waveforms can also generate complex signal returns that can provide patterns that let you discriminate objects better even with weaker returns.

Stealthflanker said:

Well i wonder why ? because if you read references the Radar Range Equation remains the same regardless of radar types. While some variables like sophistication etc may not necessarily appear or relevant in range modeling.

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Stealthflanker said:

I believe simple 4th root rules helps mainly in determining tradeoff in Radar designs and to compare radar in more sensible manner instead of relying on buzzwords which may not necessarily relevant to the discussion or difficult to visualize. the simple 4th root rules are widely used, you can check some references like George M Siouris's Radar Performance Modelling 2nd Edition or Stimson's Introduction to Airborne Radar 2nd and 3rd Edition.

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The job of a radar isn’t to project a single beam out as far as possible, but to discriminate against far away objects. What I’m talking about aren’t “buzzwords”. They’re higher level considerations for how radars perform than single beam single reflection models. The whole point of modern AESAs is to employ signal processing power beyond simple single beam single reflection interactions. You can no more use these old references to understand ESA performance than you can use a handbook on 3G cellular signals to understand how 5G cellular signals work.

latenlazy said:

Yes…because ultimately the range is determined by total transmit power. The number
elements are just a sub component for overall transmit power.

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No. because if you see the 4th root rules or if you familiar with inverse square law. The most important thing is the factor. It doesnt matter whether it is 10 Watt or 10000 Watt.

Let's give another example but now with power only. We have an AESA with 1200 elements with 10 Watt power per element. We wants to increase the element power by twice. What's the range result ?

So the reference radar has 1200*10 Watts means 12000 Watt of power and then the scaled up AESA with 20 Watt elements, makes it 24000 Watt.

Now back to inverse square law.. we will have this :

Rfac = ((1200/1200)^3*(24000/12000))^(1/4)

Rfac = 1.19 or 19% gain.

and now let's just use the TRM power.

Rfac = ((1200/1200)^3*(20/10))^(1/4)

Rfac =1.19.

Because regardless you use the entire transmit power or the TRM power the scaling factor remains the same 2.

latenlazy said:

My point is not every receiver or overall radar system has the same sensitivity or gain performance.

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Yes and i show you how to take that into account, thus allowing you to see what's the effect of having less noise/more sensitivity. and you can see hypothetical scenario too on what designer could do to offset the advantage of a radar having more TRM.

latenlazy said:

The job of a radar isn’t to project a single beam out as far as possible, but to discriminate against far away objects.

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and this is already Job of a radar since its inception. and for that there are things like Narrow beamwidth, Pulse compression. That gives you good resolution, means you can separate a target from the other. If one desire imaging there is ISAR or SAR. Both of which can be done without AESA's and well covered in radar textbook.

latenlazy said:

What I’m talking about aren’t “buzzwords”. They’re higher level considerations for how radars perform than single beam single reflection models. The whole point of modern AESAs is to employ signal processing power beyond simple single beam single reflection interactions.

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As long as you cannot provide people with something they can see and imagine. I apologize that you are spewing nothing but high tech buzzwords. It's futile to say "Hey my radar has say a STAP algorithm it must be better than yours" Without being able to show what that STAP can do.

As for me I provided simple examples people can do with their own power or just copy paste the equation to google and see result and then can discuss more. If they ask my references i will happily provided it.

latenlazy said:

You can no more use these old references to understand ESA performance than you can use a handbook on 3G cellular signals to understand how 5G cellular signals work.

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Well considering that the book are covering the APG-77, 81 and phased array designs in general etc i would call it still recent. and they serve their purpose well. There are other books too like Introduction to RF Stealth 2nd edition but it talks more about Stealth, Still it has the good ol Radar Range Equation to model the radar.

Or maybe you can show me what is the recent example i can follow ?

Stealthflanker said:

No. because if you see the 4th root rules or if you familiar with inverse square law. The most important thing is the factor. It doesnt matter whether it is 10 Watt or 10000 Watt.

Let's give another example but now with power only. We have an AESA with 1200 elements with 10 Watt power per element. We wants to increase the element power by twice. What's the range result ?

So the reference radar has 1200*10 Watts means 12000 Watt of power and then the scaled up AESA with 20 Watt elements, makes it 24000 Watt.

Now back to inverse square law.. we will have this :

Rfac = ((1200/1200)^3*(24000/12000))^(1/4)

Rfac = 1.19 or 19% gain.

and now let's just use the TRM power.

Rfac = ((1200/1200)^3*(20/10))^(1/4)

Rfac =1.19.

Because regardless you use the entire transmit power or the TRM power the scaling factor remains the same 2.

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What’s the source for the equation you’re using? I’ve never seen a radar range equation that treated the number of transmit elements as its own individual variable.

Stealthflanker said:

As long as you cannot provide people with something they can see and imagine. I apologize that you are spewing nothing but high tech buzzwords. It's futile to say "Hey my radar has say a STAP algorithm it must be better than yours" Without being able to show what that STAP can do.

As for me I provided simple examples people can do with their own power or just copy paste the equation to google and see result and then can discuss more. If they ask my references i will happily provided it.

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I’m not trying to say one radar must be better than the other. I’m saying that there are too many other unknown factors outside the simple exercise you’re doing to know how two different radars compare. The “I provide simple examples” logic is like saying you can compare the performance of two different processors by the number of transistors it has. Simplification is not a virtue. It can often mislead more than clarify.

latenlazy said:

What’s the source for the equation you’re using? I’ve never seen a radar range equation that treated the number of transmit elements as its own individual variable.

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Radar Techniques using Array Antenna by Wulf-Dieter Wirth. Chapter 4 Page 76.

latenlazy said:

I’m saying that there are too many other unknown factors outside the simple exercise you’re doing to know how two different radars compare.

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It's as if "You should not discuss this it's too complex, you should just follow what i say" That's bad for discussion.

latenlazy said:

The “I provide simple examples” logic is like saying you can compare the performance of two different processors by the number of transistors it has. Simplification is not a virtue. It can often mislead more than clarify.

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Thus why discussion exist. and it can at least to some limit. Also as you see the AESA nowadays are trending to increase the number of TRM that can be packed into the antenna, which supports the cube relationship between AESA performance with TRM number.

Stealthflanker said:

Radar Techniques using Array Antenna by Wulf-Dieter Wirth. Chapter 4 Page 76.

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Had to find a different source of the equation, but I think I see where the problem is now. I think you’re using the below equation incorrectly. You are missing that N^3 includes whole array mean power. It’s the multiple of whole array mean power with transmitter count and receiver count. Individual module power is a separate variable outside whole array mean power.

Stealthflanker said:

It's as if "You should not discuss this it's too complex, you should just follow what i say" That's bad for discussion.

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I didn’t say “you not discuss this is too complex or you should just follow what I say”. Pointing out that an argument is too simple is not trying to shut down conversation or appealing to false authority. It’s simply taking note of potential sources of error.

Stealthflanker said:

Thus why discussion exist. and it can at least to some limit. Also as you see the AESA nowadays are trending to increase the number of TRM that can be packed into the antenna, which supports the cube relationship between AESA performance with TRM number.

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I never said more modules aren’t better than less, just that you can’t get a good sense of how two AESA radars perform relatively to one another omly by looking at module counts. Anyways refer to the correction I’m pointing out to how you’re using the equation.