BAE Systems Inches Out In Public On Electronic Warfare

Cockpit, radar, helmet-mounted display, and other avionics
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popcorn

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Unread post19 Oct 2016, 12:09

See hornetfinn's thread re potential of AESA tech in a jamming role. Hard to believe that this would not have been exploited in the years since the patent was filed.

viewtopic.php?f=38&t=26802
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garrya

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Unread post19 Oct 2016, 12:11

There was another example regard standoff jamming problem , the jammer was 30km from radar , target RCS is 10 sqm , and burn through range is merely 2 km ( this jammer seem to have very good gain and transmitting power though)
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Unread post20 Oct 2016, 00:37

garrya wrote:But frequency range ( bandwidth) of a complex pulse would be much wider than 1 MHz though , is it not ?

Compressed pulse aside , bandwidth of a square pulse if a good range resolution is needed , actually pretty narrow ,around 1 MHz for 150 meters range resolution.
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Unread post20 Oct 2016, 10:58

^That seem reasonable enough , but also kind of weird, because then a short pulse with very high peak power would be harder to jam compared to a long compressed pulse with low peak power.
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Unread post20 Oct 2016, 12:12

garrya wrote:
hornetfinn wrote:4 GHz is actually a huge swath of bandwidth to jam. If we have 100 watts jammer, it would have only 0.025 Watts per MHz.

But frequency range ( bandwidth) of a complex pulse would be much wider than 1 MHz though , is it not ?


Not that much wider as eloise said and besides all modern military (and almost all commercial) radars (since 1950s) employ pulse compression (PC) technique which makes a huge difference in ECM resistance. Your example was using a very basic pulse radar with no PC at all.

garrya wrote:
hornetfinn wrote: That means the jammer ERP would actually be only 17 dBi instead of 53 dBi. That change would directly mean that burn through range would become about 16 km instead.

TBH iam not so good with number so can you elaborate a bit more ?
anyway, 16 km burn through range still seem extremely short for target with RCS = 10 m2 , that is well within range of IR sensor


100 Watts is 50 dBm and along with3 dBi Antenna that becomes 53 dBm. MHz is the basic unit used in these calculations and 100 Watts divided by 4000 (4 GHz) becomes 0.025 Watts which is how much jamming energy there is per MHz. That's equal to 14 dBm. With the 3 dBi antenna, that becomes 17 dBm to be used in these calculations.

Yes, 16 km BT range is very short, but that's only accounting for the jamming energy which is spread over such a large bandwidth. When you take into account pulse compression, doppler processing and other such methods, the whole thing changes drastically as radar gets huge performance improvements due to processing gain.

garrya wrote:
hornetfinn wrote:Another thing is that required J/S is only 2 dB for jamming to be effective. With modern radars the processing gain of complex coded waveforms is much higher and can easily be 30-40 dB (or even higher).

That a fair point but as far as i know , while angle jamming technique require very high J/S ratio to be effective , range jamming technique doesnt seem to need J/S ratio that high
Image


You may notice that range jamming techniques are only under Pulsed radar type. That means basic pulse radar without any of the techniques I mentioned. Pretty much all modern radars use monopulse technique which makes them very hard to jam with techniques that worked well against pulsed radars.

garrya wrote:
hornetfinn wrote:Since usually detection requires about 13 dB SNR, the required J/S would be 17 to 27 dB in this case. That would further increase the range to well over 100 km. 40 dB processing gain would bring this to 355 km or so.

I dont really get this part , can you elaborate ?


I meant processing gain of 30 to 40 dB where we subtract the required SNR for detection (13 dB is used often as rule of thumb for automatic detectors) which makes the required J/S 17 to 27 dB.

garrya wrote:
hornetfinn wrote: Radars also have higher antenna gain than 30 dBi. A typical fighter radar has antenna gain of 30-40 dBi and larger surveillance and ground based fire control radars can have even higher antenna gain.

I know that ground radar can have very high gain ( their size is practically unlimited after all ) , but i dont think average fighter radar ( aka APG-81 ) has higher gain than 30 dB given their size and operating frequency


You can easily calculate radar antenna gains with these formulas:
http://www.phys.hawaii.edu/~anita/new/p ... tennas.pdf

With 50 percent efficiency a 60 cm antenna of F-16 AN/APG-68 has gain of 32.55 dB in middle of X-band. For 91.4 cm dish for F-14 and F-15 we get antenna gain of 36.2 dB. I've seen figures of about 37 dB for F-14 antenna, which would suggest antenna efficiency of about 60 percent which is possible for planar array radar. AESA antennas can have efficiency of 70 to 80 percent and that would result in 1-2 dB higher antenna gain. With higher frequency gain increases and lower frequency gain decreases.
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Unread post20 Oct 2016, 13:13

hornetfinn wrote:100 Watts is 50 dBm and along with3 dBi Antenna that becomes 53 dBm. MHz is the basic unit used in these calculations and 100 Watts divided by 4000 (4 GHz) becomes 0.025 Watts which is how much jamming energy there is per MHz. That's equal to 14 dBm. With the 3 dBi antenna, that becomes 17 dBm to be used in these calculations.
Yes, 16 km BT range is very short

If the jamming power is 1 kW but J/S is 20 dB
what would be the Range burn through for our calculation ?

hornetfinn wrote:You may notice that range jamming techniques are only under Pulsed radar type. That means basic pulse radar without any of the techniques I mentioned. Pretty much all modern radars use monopulse technique which makes them very hard to jam with techniques that worked well against pulsed radars. .

AFAIK , monopulse technique is only for better angle tracking capabilities , range tracking should be unaffected , and even monopulse seem to be rather vulnerable to blinking jamming
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hornetfinn wrote:SinI meant processing gain of 30 to 40 dB where we subtract the required SNR for detection (13 dB is used often as rule of thumb for automatic detectors) which makes the required J/S 17 to 27 dB..

So basically , for example : if APG-81 detect a target at 100 km , the SNR has to be at least 13dB ? shouldn't more sensitive receiver and better processing power require smaller SNR ?

hornetfinn wrote:You can easily calculate radar antenna gains with these formulas:
http://www.phys.hawaii.edu/~anita/new/p ... tennas.pdf
With 50 percent efficiency a 60 cm antenna of F-16 AN/APG-68 has gain of 32.55 dB in middle of X-band. For 91.4 cm dish for F-14 and F-15 we get antenna gain of 36.2 dB. I've seen figures of about 37 dB for F-14 antenna, which would suggest antenna efficiency of about 60 percent which is possible for planar array radar. AESA antennas can have efficiency of 70 to 80 percent and that would result in 1-2 dB higher antenna gain. With higher frequency gain increases and lower frequency gain decreases.

Doesnt seem to be very significant to be fair
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Unread post20 Oct 2016, 14:05

garrya wrote:
hornetfinn wrote:100 Watts is 50 dBm and along with3 dBi Antenna that becomes 53 dBm. MHz is the basic unit used in these calculations and 100 Watts divided by 4000 (4 GHz) becomes 0.025 Watts which is how much jamming energy there is per MHz. That's equal to 14 dBm. With the 3 dBi antenna, that becomes 17 dBm to be used in these calculations.
Yes, 16 km BT range is very short

If the jamming power is 1 kW but J/S is 20 dB
what would be the Range burn through for our calculation ?

hornetfinn wrote:You may notice that range jamming techniques are only under Pulsed radar type. That means basic pulse radar without any of the techniques I mentioned. Pretty much all modern radars use monopulse technique which makes them very hard to jam with techniques that worked well against pulsed radars. .

AFAIK , monopulse technique is only for better angle tracking capabilities , range tracking should be unaffected , and even monopulse seem to be rather vulnerable to blinking jamming
Image

hornetfinn wrote:SinI meant processing gain of 30 to 40 dB where we subtract the required SNR for detection (13 dB is used often as rule of thumb for automatic detectors) which makes the required J/S 17 to 27 dB..

So basically , for example : if APG-81 detect a target at 100 km , the SNR has to be at least 13dB ? shouldn't more sensitive receiver and better processing power require smaller SNR ?

hornetfinn wrote:You can easily calculate radar antenna gains with these formulas:
http://www.phys.hawaii.edu/~anita/new/p ... tennas.pdf
With 50 percent efficiency a 60 cm antenna of F-16 AN/APG-68 has gain of 32.55 dB in middle of X-band. For 91.4 cm dish for F-14 and F-15 we get antenna gain of 36.2 dB. I've seen figures of about 37 dB for F-14 antenna, which would suggest antenna efficiency of about 60 percent which is possible for planar array radar. AESA antennas can have efficiency of 70 to 80 percent and that would result in 1-2 dB higher antenna gain. With higher frequency gain increases and lower frequency gain decreases.

Doesnt seem to be very significant to be fair


A 6 dBi improvement in antenna gain would give you something like double the range since you are improving total system gain by 12 dBi (+6 dBi on both transmit and receive).
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Unread post20 Oct 2016, 17:25

castlebravo wrote:A 6 dBi improvement in antenna gain would give you something like double the range since you are improving total system gain by 12 dBi (+6 dBi on both transmit and receive).

Gain on receiving phase here can probably be ignored because radar will receive jamming signals too
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Unread post20 Oct 2016, 20:23

There is one easier way to settle this debate, we should as gums if F-16 using ALQ-184 or any other jamming pod can get into the merge with F-15 without being engaged from BVR, then go from there
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Unread post21 Oct 2016, 09:01

eloise wrote:There is one easier way to settle this debate, we should as gums if F-16 using ALQ-184 or any other jamming pod can get into the merge with F-15 without being engaged from BVR, then go from there

35AoA and spazsinbad are also pilot AFAIK, maybe they can contribute their opinion
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Unread post21 Oct 2016, 09:17

garrya wrote:
hornetfinn wrote:100 Watts is 50 dBm and along with3 dBi Antenna that becomes 53 dBm. MHz is the basic unit used in these calculations and 100 Watts divided by 4000 (4 GHz) becomes 0.025 Watts which is how much jamming energy there is per MHz. That's equal to 14 dBm. With the 3 dBi antenna, that becomes 17 dBm to be used in these calculations.
Yes, 16 km BT range is very short

If the jamming power is 1 kW but J/S is 20 dB
what would be the Range burn through for our calculation ?


In that case the 20Log Rbt = 120 - 24 -71 + 10 + 2 = 37

Rbt = Antilog (37 / 20) = Antilog (1.85) = 70.8 km.

That's assuming the jammer jams the whole 4 GHz X-Band with 1 kW of power. If the jammer is exactly at the same frequency and bandwidth as the radar the range would be slightly less than 800 meters or about 1000 times shorter.

garrya wrote:
hornetfinn wrote:You may notice that range jamming techniques are only under Pulsed radar type. That means basic pulse radar without any of the techniques I mentioned. Pretty much all modern radars use monopulse technique which makes them very hard to jam with techniques that worked well against pulsed radars. .

AFAIK , monopulse technique is only for better angle tracking capabilities , range tracking should be unaffected , and even monopulse seem to be rather vulnerable to blinking jamming
Image


Range gate jamming techniques can be pretty easily be dealt with using variable PRF (jittering), monitoring the received signal strength, using leading edge tracking and very importantly using pulse to pulse frequency hopping. Range gate jamming techniques require that radar signal is replicated with high precision and very fast and that is very difficult with modern radars which incidentally also use all of the techniques mentioned. DRFM techniques can make ange gate jamming techniques effective but it's by no means any magic bullet. It might be able to break the radar track but modern AESAs can regain tracking very quickly, so the usefulness is somewhat questionable. Also if radar uses leading-edge tracking, even DRFM range gate jamming is not effective. Monopulse technique was developed for better angle tracking but it also protects against range gate jamming as the radar has more signal information to detect such jamming. It makes the jammer needing to be far more precise and subtle in operation to work.

Blinking jamming is formation jamming that requires two or more aircraft synchronously doing jamming at certain distance between each other and radar being certain simple type of mechanical tracking radar. It tries to overwhelm the angle tracking servo of the antenna as the radar moves the antenna from one jamming source to another. With modern systems it's basically only radar guided missiles that might be affected and even then it requires that missile seeker was designed without this in mind. Also if missile gets updates from outside, this method would have no effect.

garrya wrote:
hornetfinn wrote:SinI meant processing gain of 30 to 40 dB where we subtract the required SNR for detection (13 dB is used often as rule of thumb for automatic detectors) which makes the required J/S 17 to 27 dB..

So basically , for example : if APG-81 detect a target at 100 km , the SNR has to be at least 13dB ? shouldn't more sensitive receiver and better processing power require smaller SNR ?


That's just a rule of thumb and exact details depend on system. However, the SNR is a function of probability of detection and false alarm rate and these are universal. More sensitive receiver lowers the SNR degradation in the radar system but does not affect the required SNR itself. Better processing can affect the required SNR especially with multiple detections. 13 dB is a rule of thumb for a single pulse detection. Things can get pretty complicated with real world radar systems as they pretty much all employ pulse integration which can improve required SNR significantly.

garrya wrote:
hornetfinn wrote:You can easily calculate radar antenna gains with these formulas:
http://www.phys.hawaii.edu/~anita/new/p ... tennas.pdf
With 50 percent efficiency a 60 cm antenna of F-16 AN/APG-68 has gain of 32.55 dB in middle of X-band. For 91.4 cm dish for F-14 and F-15 we get antenna gain of 36.2 dB. I've seen figures of about 37 dB for F-14 antenna, which would suggest antenna efficiency of about 60 percent which is possible for planar array radar. AESA antennas can have efficiency of 70 to 80 percent and that would result in 1-2 dB higher antenna gain. With higher frequency gain increases and lower frequency gain decreases.

Doesnt seem to be very significant to be fair


Do you mean AESA antenna gain over MSA antenna? That's just one improvement and the difference alone means 15 to 30 percent increase in effective range. It doesn't mean that much for main lobe jamming resistance alone, but due to much lower sidelobes makes sidelobe jamming and detectability of radar much harder. Of course electronic scanning also makes the job of jammer much harder as there is no way of predicting when the main lobe will be directed towards it. Jammers can predict the time when they can do their work against MSA radars, but that's not possible with phased array radars unless they are really badly designed. Of course the difference also means that AESA radar will have 15 to 30 percent range advantage against MSA or PESA radars. And that's just with having better antenna gain. Then we have higher average power, lower losses, much wider total bandwidth, waveform agility and other such AESA advantages and suddenly all add up to huge advantages and threre is a lot of room for development in each of these areas still.

Going from 30 to say 36 dB antenna gain means that the BT range is doubled. Doesn't mean much if BT range is the original 251 meters, but is huge when BT is say 100 km for 30 dB antenna and 200 km for 36 dB antenna.
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Unread post21 Oct 2016, 11:01

hornetfinn wrote:In that case the 20Log Rbt = 120 - 24 -71 + 10 + 2 = 37

Rbt = Antilog (37 / 20) = Antilog (1.85) = 70.8 km.

That's assuming the jammer jams the whole 4 GHz X-Band with 1 kW of power. If the jammer is exactly at the same frequency and bandwidth as the radar the range would be slightly less than 800 meters or about 1000 times shorter.

burn through range square is proportional to RCS , so if the burn through distance against target with RCS = 10 m2 is 70.8 km , then the burn through distance against target with RCS =1 m2 is 20 km , hmm seem very short , that near visual range already
Image

hornetfinn wrote:Range gate jamming techniques can be pretty easily be dealt with using variable PRF (jittering), monitoring the received signal strength, using leading edge tracking and very importantly using pulse to pulse frequency hopping

Iam under the impression that PRF jittering and frequency hopping can be dealt with by spread out jamming power for the whole spectrum (barrage noise) ?
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Unread post21 Oct 2016, 13:11

garrya wrote:
hornetfinn wrote:In that case the 20Log Rbt = 120 - 24 -71 + 10 + 2 = 37

Rbt = Antilog (37 / 20) = Antilog (1.85) = 70.8 km.

That's assuming the jammer jams the whole 4 GHz X-Band with 1 kW of power. If the jammer is exactly at the same frequency and bandwidth as the radar the range would be slightly less than 800 meters or about 1000 times shorter.

burn through range square is proportional to RCS , so if the burn through distance against target with RCS = 10 m2 is 70.8 km , then the burn through distance against target with RCS =1 m2 is 20 km , hmm seem very short , that near visual range already
Image


That just shows how important RCS reduction is for reducing detectability and how it works with jamming. Of course that's still pretty far from realistic modern radar and jammer system. The example is just a very basic one. In real world radars have much bigger processing and antenna gains. Jammers on the other hand will try to use narrower bandwidths and combination of jamming techniques to counter that. Generally no realistic jammer is going to have that huge advantage against realistic radar system. Some WW2 radar types with one fixed frequency might be that easily jammed, but not more modern ones.

garrya wrote:
hornetfinn wrote:Range gate jamming techniques can be pretty easily be dealt with using variable PRF (jittering), monitoring the received signal strength, using leading edge tracking and very importantly using pulse to pulse frequency hopping

Iam under the impression that PRF jittering and frequency hopping can be dealt with by spread out jamming power for the whole spectrum (barrage noise) ?


Barrage noise jamming is pretty sure way of jamming everything if you have enough power. Problem however is that it requires a huge power advantage to really work against modern radars. That can be achieved by having huge amount of RF power which is bad because you become a very bright radar beacon for everybody. Besides, even a 1 square meter RCS fighter would require a huge amount of power (like Megawatts) to really be able to be effective at realistic ranges and that kind of power would be impossible to fit inside fighter aircraft. Even dedicated jammer aircraft can generate kilowatts of power.

Another way is to have highly directional jamming antennas which is good if you can direct the beam to right direction but bad if you can't (no effect if radar is not inside the jamming beam). Another good way is to have very smart jamming methods which lowers the power requirements and allows better response to radars. A really good way is to reduce your own RCS as that doesn't have any drawbacks for effectiveness like other methods. Having 100 times lower RCS is a really good thing without jamming and with jamming it's really great. You might notice that F-35 (and F-22 I'm sure) employ all of these methods and latest 4th gen fighters are trying to do their best in all areas. Of course 4th gen fighters can't beat the 30-50 dB RCS advantage F-35 and F-22 have due to their VLO stealth. That'd require having 100-10,000 times more jamming power or smarter jamming systems. Of course either is highly doubtful.
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Unread post21 Oct 2016, 15:03

hornetfinn wrote:In that case the 20Log Rbt = 120 - 24 -71 + 10 + 2 = 37
Rbt = Antilog (37 / 20) = Antilog (1.85) = 70.8 km.

That's assuming the jammer jams the whole 4 GHz X-Band with 1 kW of power. If the jammer is exactly at the same frequency and bandwidth as the radar the range would be slightly less than 800 meters or about 1000 times shorter.
That just shows how important RCS reduction is for reducing detectability and how it works with jamming. Of course that's still pretty far from realistic modern radar and jammer system. The example is just a very basic one. In real world radars have much bigger processing and antenna gains. Jammers on the other hand will try to use narrower bandwidths and combination of jamming techniques to counter that. Generally no realistic jammer is going to have that huge advantage against realistic radar system. Some WW2 radar types with one fixed frequency might be that easily jammed, but not more modern ones.
Barrage noise jamming is pretty sure way of jamming everything if you have enough power. Problem however is that it requires a huge power advantage to really work against modern radars. Besides, even a 1 square meter RCS fighter would require a huge amount of power (like Megawatts) to really be able to be effective at realistic ranges and that kind of power would be impossible to fit inside fighter aircraft. Even dedicated jammer aircraft can generate kilowatts of power.

Based on our original example , if we modify the number a tiny bit :
if the jammer power is 1 kW
jammer gain is 3dBi
radar power is 10 kW
radar gain = 30dBi
J/S ratio required is 20 dB
operating band width of radar is between 8-12 Ghz
assuming the kind of jamming used is barrage noise so factors like PRF jittering and frequency hopping , pulse compression can be ignored
the burn through distance would be 70 km if target RCS is 10 m2 , about 20 km if target RCS is 1 m2 and so on , i dont think much more power will be required because 20 km burn through distance seem good enough.
Then one thing iam not so clear about the original function ,when they give number for the jammer and radar effective radiated power , are those average power or peak ? , 10 kW average power for airborne fighter radar seem overly high , i would think about 2-3 kW top.
Moreover, iam thinking , since we know AESA radar can be used in jamming role , what if the legacy fighter just use its radar for jamming ( since obviously it wont be able to detect stealth aircraft by its radar anyway) ? then we have jammer gain and effective radiated power equal to radar ?????


hornetfinn wrote:That can be achieved by having huge amount of RF power which is bad because you become a very bright radar beacon for everybody.

to be fair though , the same thing can be said when aircraft using their radar , even though to lesser extent. I know that there are LPI radar and what not , but still , if the small GPS antenna in mobiles phone , JDAM can detect GPS signal from satellite hundred thounsand miles aways then i think modern RWR should do well again radar at distance 200 km or less.
hornetfinn wrote: Another good way is to have very smart jamming methods which lowers the power requirements and allows better response to radars. A really good way is to reduce your own RCS as that doesn't have any drawbacks for effectiveness like other methods. Having 100 times lower RCS is a really good thing without jamming and with jamming it's really great. You might notice that F-35 (and F-22 I'm sure) employ all of these methods and latest 4th gen fighters are trying to do their best in all areas. Of course 4th gen fighters can't beat the 30-50 dB RCS advantage F-35 and F-22 have due to their VLO stealth. That'd require having 100-10,000 times more jamming power or smarter jamming systems. Of course either is highly doubtful.

This is undeniable , ofcourse low RCS can bring unparalleled jamming advantages , i agree that legacy aircraft wont be able to compete with fifth gen in SEAD , the gap is too enormous. However, in air to air role , i am thinking that a 4 gen fighter , with powerful enough jammer can reduce fighter radar burn through distance down to near visual range ( since fighter radar isnt really that powerful after all ).While the jammer on stealth aircraft would still be alot more effective , it is irrelevance in this case because if the jammer on legacy aircraft can bring burn through distance down to let say 20-25 km , then even if the jammer on VLO platform can bring burn through distance down to 2 km , it still doesnt matter , because at those distance electro optic sensors should work quite well.
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Unread post22 Oct 2016, 10:02

To me that is key: it is not only stealth; it is the combination of the EOS and the radar to be able to build a comprehensive picture. In that engagement I talked about at Nellis, in Red Flag, the ability to be in a cockpit with a God’s-eye view of what is going on in the world was such an advantage over a fourth-generation fighter – and arguably one of the best fourth-generation fighters in existence, the F15. But even with a DRFM jamming pipe, we still had no chance in those particular engagements.

https://theaviationist.com/2013/06/19/f ... by-rafale/
If we were to believe the word of F-15 pilot who join exercise vs F-22 then jamming pod still doesnt help him get into visual range.
And GaN modules are said to have much wider bandwidth compare to GaAs modules so that will improve radar jamming resistance significantly in future.APG-81 will have GaN sooner or later but stealth cant be retrofitted to legacy aircraft .
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