PLAN Sovremenny DDG 136, 137, 138 & 139 Thread


nlalyst

Junior Member
Registered Member
I made a booboo in my calculation above.

SPG-62 avg illum power: 10kW, range 240km (pessimistic)
SPG-51 avg illum power: 4 kW

Sqrt(10/4)=1.58. Therefore, the pessimistic illumination range estimate for SPG-51 is 240km/1.58 = 151.9km
SPG-51 antenna diamter is 2.5m versus 2.29m for SPG-62. This gives a 19% advantage in gain, which should translate to 9% advantage in illumination range, which would get us very close to 90nm (167km).
 
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nlalyst

Junior Member
Registered Member
One more thing to add, with regards to the Fregat and frequency scan. The longer the distance between the radiator to another, the greater the angle the beam that can be phase shifted. Another factor that is difficult to measure but is important to how far the angle the beam can be phase shifted, is the length of the S or snake feed that you see on the sides. Without knowing the actual length of the S feed, a longer distance between each radiator means each sequential radiator gets a greater delay time.
Yes, but I don't think those are the only limitations with regard to beam angle. Increasing the physical spacing between the radiators will introduce grating lobes and lower the practical beam angle or scan FOV. On a phased array to get +/- 60 degree FOV you need at most 0.5 lambda spacing.

The SPS-48 goes even beyond that, as it can scan up to 69 degrees in elevation. Its linear arrays are stacked at double the density compared to Fregat and the sepertine feed appears longer (although in Fregat a part might be tucked behind the antenna?). Take a look at this photo. I counted about 94 linear arrays.
1920px-Radar_antennas_on_USS_Theodore_Roosevelt_CVN-71.jpg
 

Tam

Colonel
Registered Member
Yes, but I don't think those are the only limitations with regard to beam angle. Increasing the physical spacing between the radiators will introduce grating lobes and lower the practical beam angle or scan FOV. On a phased array to get +/- 60 degree FOV you need at most 0.5 lambda spacing.

The SPS-48 goes even beyond that, as it can scan up to 69 degrees in elevation. Its linear arrays are stacked at double the density compared to Fregat and the sepertine feed appears longer (although in Fregat a part might be tucked behind the antenna?). Take a look at this photo. I counted about 94 linear arrays.
1920px-Radar_antennas_on_USS_Theodore_Roosevelt_CVN-71.jpg


I neglected to mention that a frescan works differently from other phase array. The distance between radiators is a function of the maximum angle, the frequency and the highest degree of phase shift it can attain. So actual frequency is not greater than the distance of the radiators and would be less of that.

Radiators in frescan do not radiate simultaneously but is sequentially delayed and every radiator has a slightly different frequency caused by the sequential delay.

Lambda spacing is between elements within the same radiator.
 

Tam

Colonel
Registered Member
I made a booboo in my calculation above.

SPG-62 avg illum power: 10kW, range 240km (pessimistic)
SPG-51 avg illum power: 4 kW

Sqrt(10/4)=1.58. Therefore, the pessimistic illumination range estimate for SPG-51 is 240km/1.58 = 151.9km
SPG-51 antenna diamter is 2.5m versus 2.29m for SPG-62. This gives a 19% advantage in gain, which should translate to 9% advantage in illumination range, which would get us very close to 90nm (167km).

Not really. You have the declassified pdf at .mil that I showed you already.
 

Tam

Colonel
Registered Member
The mountain wasn't the point. You can inverse the picture: put the radar at sea-level and the threat at altitude. The point was to demonstrate what the tracking and illumination capabilities of the upgraded SPG-51D are. Tracking a sea-skimming missile is a lot more challenging than tracking an aircraft flying at 1km+ altitude. If the SPG-51D was credited to be able to track and illuminate sea-skimming missiles at ranges well beyond 45nm=83.34km, then it would do even better against aircraft whose RCS is 10-100 larger than the missile and who don't fly as low.



First, it is SPG-51D Mod 15 NTU that is installed on the ROC Kidd's. Second, the plots in that pdf are authors's simulations where he plugged in his estimation of radar parameters into the radar equation. Judging by the range he gave to the SM-2MR he must've been used the early variant of the missile. The same could then be said of the SPG-51 radar.

The SM-2MR Blk III on the ROC Kidd have a range of 90nm and the ship's Tartar combat system received the NTU upgrade in the 88-90.


In AEGIS ships, the SPG-62 illuminators are slaved to SPY-1. On the Kidd, the SPG-51 needs to be able to track the target in order to point the illumination beam correctly, which happens automatically since they share the same antenna. Thanks to inertial guidance of SM-2 missiles, the tracking/illumination can still be timeshared among a large number of missiles, although less than in AEGIS for the reason discussed above. For the initial part of the engagement, the SPS-48 track is sufficient (otherwise it couldn't time share).

You keep running into contradictions. We just saw in the example above that SPG-51D is capable of engaging small sea-skimming missiles at a distance of well beyond 45nm ( if positioned at a mountaintop). Against aircraft with RCS up to 100 larger it should theoretically be able to do triple that (quadratic root relation of range to RCS).

Your argument is basically that ROC's Kidd destroyer and F-16 fighter are mismatched to their anti-air weapons of choice and can't take advantage of the full capability of the SM-2MR Block IIIA missile and the AIM-120C-7 missile, respectively. On the other hand, you claim that the PRC's Sovremmeny destroyers and J-10 aircraft are perfectly matched to their weapon of choice. Please.


SPG-51D has enough illumination power. As discussed previously, it has a slightly larger antenna and 40% of the output RF power compared to SPG-62. Increasing power output by 60% will give you 26% more illumination range (square root relation). The latter's minimum illumination capability is 240km, which is the range of the SM-2ER Block IV missile, but is likely even more as it supports the longer range SM-6. Taking 240km as the baseline, we can derive the SPG-51D max illumination range to be 190km.

Finally, I guess you know that modern SAM's don't fly the shortest path from A to B? In fact, not flying the straight line to target is what gives them ultimately more range due to superior aerodynamics.


The picture isn't at scale, and you might as well assume the slant range of the SPG-51 to the target is maybe about 70km or less given the Tico's radar horizon might be around 30km.

SPS-48 problem is that it can only track what is in front of the array, not its back. Dual backing not only doubles the rate of update, it also covers double the volume.

Going back to the SPS-48, the length of its S feed also means it takes a relatively longer time for the signal to go from one end of the feed to the other. That increases the length of time to do a scan, which means slower vertical scan, so longer time between tracks. That's the point of some radars having shorter S-feeds.

With regards to the F-16 why did you switch the argument from AIM-7 to the AIM-120C7? ARH missiles can compensate for the distance because of the seeker's terminal range. Its your inertial+midphase+terminal range total. AIM-120 doesn't use the X-band CWI illuminator either. The X-band illuminator is special only for the ROC's APG-66 to make the radar compatible with the ROC's existing stock of Sparrows.

You keep on going back to the time sharing. It does not matter that much because you only have two illuminators. You cannot put too many missiles in the sky because missiles cannot loiter, and if a missile is "waiting" for the next target, it still consumes its fuel and it may end up in a position that is unfavorable for intercepting a new target when the position of the new target is discovered. And then you have an issue with the datalinks. These are not magic. Where and what's your antenna that is used to work for this? If its omnidirectional, you have a problem that enemy EW will discover the signal and jam it. If its omnidirectional, you won't have high gain and your range is limited. If the datalink is directional, in order to hide from enemy EW and gain range, where is the high gain antenna then? Usually the best place is to put it in the radar itself, so it shares the same dish. You don't have to sync a separate high gain antenna. However, putting it on the same dish means the missile will have to be in the same beamwidth of the radar to obtain that signal. Also with mechanical high gain antennas, that's one antenna per missile and it still needs to continually track the missile. How many datalinks can you see on the Kidd? This is another point of using a phase array and putting the datalink into it.

Once again, you keep on claiming despite the declassified .mil document that says otherwise. Oh you think the plot is made by calculations and not from actual testing? Where is your basis on that? Do you have any details on the NTU upgrade that suggest they changed the illumination transmitter from the 4kw?

You're making range calculations without taking account of the radar's antenna gain, target radar cross section and the missile's minimum receivable signal? Even if you reach that far, that's not the point. The point is the strength of the reflection from the target versus the size, gain, and the minimum receivable signal on the missile antenna that the missile will accept as a lock.
 
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nlalyst

Junior Member
Registered Member
Not really. You have the declassified pdf at .mil that I showed you already.
Can you point out what's wrong with those numbers/reasoning instead?

You keep waving that .mil pdf, but have you actually read the text of the thesis or did you just look at the pictures? If you did, then you would know that the student generated those plots by writing a program that plots the radar range curves based on a two-way radar equation, an assumed probability of detection, a generic noise figure for microwave receivers, etc. I'll even give you hint: it's equation 2.18. The parameters he plugged into the equation were just guesses: that's obvious from all the "Assume" statements he uses before listing the parameters without any references. Take a look at his results: he computed 46km as the maximum range for SPG-51 against a 1m2 target. At the same time, we've seen that the NTU SPG-51D can track a 0.1m2 sea-skimming target from well beyond 70km.

With regards to the F-16 why did you switch the argument from AIM-7 to the AIM-120C7? ARH missiles can compensate for the distance because of the seeker's terminal range. Its your inertial+midphase+terminal range total. AIM-120 doesn't use the X-band CWI illuminator either. The X-band illuminator is special only for the ROC's APG-66 to make the radar compatible with the ROC's existing stock of Sparrows.
I didn't. You did. My example from the beginning was the AIM-120C7, while you keep bringing in the AIM-7. The point was inertial midcourse guidance and whether the radar needs to track the missile or not. Remember?

You keep on going back to the time sharing. It does not matter that much because you only have two illuminators. You cannot put too many missiles in the sky because missiles cannot loiter, and if a missile is "waiting" for the next target, it still consumes its fuel and it may end up in a position that is unfavorable for intercepting a new target when the position of the new target is discovered.
The missiles will not have to wait for the target: they will be cued by the search radar into an intercept course. The combat system is programmed not to fire more missiles than it can handle. The number of inflight missiles will be limited by the time the SPG-51D needs to be dedicated for the homing and endgame phase per target. The further away the target is the longer this time will be, and the closer it is the shorter. However, this information is not available.
And then you have an issue with the datalinks. These are not magic. Where and what's your antenna that is used to work for this? If its omnidirectional, you have a problem that enemy EW will discover the signal and jam it. If its omnidirectional, you won't have high gain and your range is limited. If the datalink is directional, in order to hide from enemy EW and gain range, where is the high gain antenna then? Usually the best place is to put it in the radar itself, so it shares the same dish. You don't have to sync a separate high gain antenna. However, putting it on the same dish means the missile will have to be in the same beamwidth of the radar to obtain that signal. Also with mechanical high gain antennas, that's one antenna per missile and it still needs to continually track the missile. How many datalinks can you see on the Kidd? This is another point of using a phase array and putting the datalink into it.
I don't have this information, sorry. All I know is that ROC's ships use an X-band 2T uplink and a S-band downlink to communicate with the SM-2 missiles during midcourse guidance.
Once again, you keep on claiming despite the declassified .mil document that says otherwise. Oh you think the plot is made by calculations and not from actual testing? Where is your basis on that? Do you have any details on the NTU upgrade that suggest they changed the illumination transmitter from the 4kw?
I explained above. Clearly you didn't read the text but you hold on to it like it's the Bible. It's just a master thesis from 1984.

The NTU upgrade for the Kidd's happened 5 years later. The ships got the ultra long range SPS-48E S-band radar, the long range SPS-49 L-band radar and they upgraded the Tartar/SPG-51D to Mod 15 NTU Baseline to support SM-2 Blk IIIA missiles.
You're making range calculations without taking account of the radar's antenna gain, target radar cross section and the missile's minimum receivable signal? Even if you reach that far, that's not the point. The point is the strength of the reflection from the target versus the size, gain, and the minimum receivable signal on the missile antenna that the missile will accept as a lock.
I was making a relative estimate of the illuminator capability, not the radar, based on the capability of SPG-62: that way I don't need the target RCS nor the minimum receivable signal. They will scale accordingly. The seekers are the same in SM-2MR and SM-2ER, the latter just has a booster to push it further. The average power of SPG-62 and SPG-51 is published, as are their antenna dimensions. From the latter, the antenna gain can be computed. That's all the information that's needed. Why don't you run those numbers and show me what you get, instead of just throwing hurdles?

There's a separate question of whether the SPG-51D NTU C-band radar can track targets at that range. That was addressed by observing that it was capable of tracking a sea-skimming 0.1m2 target (cross section of Tomahawk missile) at well beyond 70km, so it should easily track a 10m2 (J-15) target at double that range.
 

nlalyst

Junior Member
Registered Member
And then you have an issue with the datalinks. These are not magic. Where and what's your antenna that is used to work for this? If its omnidirectional, you have a problem that enemy EW will discover the signal and jam it. If its omnidirectional, you won't have high gain and your range is limited. If the datalink is directional, in order to hide from enemy EW and gain range, where is the high gain antenna then?
I searched a bit more and found out that the Kidd destroyers received 4 AN/SYR-1 phased array units to handle S-band downlinks from SM-2MR missiles. This could also be the means by which the ship could track a missile and point the SPG-51 towards it to issue uplink updates if necessary, in addition to the missile's own idea of its position based on its INS unit that is sent back via the downlink. You can see them in the photo below:
1617366550300.png

In the first evolution of the 2T combat system to support SM-2s with inertial guidance, the uplink appears to be handled by the fire control radar, according to JHU APL digest:
1617368044600.png

The NTU added upgraded radars and radar data fusion via AN/SYS-2, to deal with fast moving anti-ship missiles. Here is an illustration of the test setup for the NTU, with an illustration of how uplink and donwlink are handled on a CG ship:
1617368426600.png

A bit of context on the AN/SYS-2:
1617367235100.png
 

Tam

Colonel
Registered Member

Can you point out what's wrong with those numbers/reasoning instead?

You keep waving that .mil pdf, but have you actually read the text of the thesis or did you just look at the pictures? If you did, then you would know that the student generated those plots by writing a program that plots the radar range curves based on a two-way radar equation, an assumed probability of detection, a generic noise figure for microwave receivers, etc. I'll even give you hint: it's equation 2.18. The parameters he plugged into the equation were just guesses: that's obvious from all the "Assume" statements he uses before listing the parameters without any references. Take a look at his results: he computed 46km as the maximum range for SPG-51 against a 1m2 target. At the same time, we've seen that the NTU SPG-51D can track a 0.1m2 sea-skimming target from well beyond 70km.


I didn't. You did. My example from the beginning was the AIM-120C7, while you keep bringing in the AIM-7. The point was inertial midcourse guidance and whether the radar needs to track the missile or not. Remember?


The missiles will not have to wait for the target: they will be cued by the search radar into an intercept course. The combat system is programmed not to fire more missiles than it can handle. The number of inflight missiles will be limited by the time the SPG-51D needs to be dedicated for the homing and endgame phase per target. The further away the target is the longer this time will be, and the closer it is the shorter. However, this information is not available.

I don't have this information, sorry. All I know is that ROC's ships use an X-band 2T uplink and a S-band downlink to communicate with the SM-2 missiles during midcourse guidance.

I explained above. Clearly you didn't read the text but you hold on to it like it's the Bible. It's just a master thesis from 1984.

The NTU upgrade for the Kidd's happened 5 years later. The ships got the ultra long range SPS-48E S-band radar, the long range SPS-49 L-band radar and they upgraded the Tartar/SPG-51D to Mod 15 NTU Baseline to support SM-2 Blk IIIA missiles.

I was making a relative estimate of the illuminator capability, not the radar, based on the capability of SPG-62: that way I don't need the target RCS nor the minimum receivable signal. They will scale accordingly. The seekers are the same in SM-2MR and SM-2ER, the latter just has a booster to push it further. The average power of SPG-62 and SPG-51 is published, as are their antenna dimensions. From the latter, the antenna gain can be computed. That's all the information that's needed. Why don't you run those numbers and show me what you get, instead of just throwing hurdles?

There's a separate question of whether the SPG-51D NTU C-band radar can track targets at that range. That was addressed by observing that it was capable of tracking a sea-skimming 0.1m2 target (cross section of Tomahawk missile) at well beyond 70km, so it should easily track a 10m2 (J-15) target at double that range.


We have not seen the NTU SPG-51D illuminate a 0.1m2 sea skimming target well beyond 70km. You added the 20nm on your own based on your assumption. You don't know what is the distance of the Tico is to the SPG-51, and I don't know where you get the 25 nm for the ship horizon. With the SPY-1, the radar horizon for such would be relatively low.

You suddenly made a jump to 0.1m2? Based on targeting the BQM-74, which is an old target drone with straight wings designed in the sixties, you are suddenly assuming that is meant to simulate a Tomahawk at 0.1m2. I am not sure how you can connect the Tomahawk to 0.1m2 either given its lack of stealth features and straight wings but that's another story.

Good enough on the SYS-2. That's the typical track combine.

Answering what pointed earlier. A direct path from A to B is the fastest way of interception and the highest PK. Sure you can take a more ballistic path high up and dive down, which extends range, but it can also potentially reduce the PK.

I am sure the SPG-51D with the C-band can track targets at 70km, that's not a problem.
 
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nlalyst

Junior Member
Registered Member
We have not seen the NTU SPG-51D illuminate a 0.1m2 sea skimming target well beyond 70km. You added the 20nm on your own based on your assumption. You don't know what is the distance of the Tico is to the SPG-51, and I don't know where you get the 25 nm for the ship horizon. With the SPY-1, the radar horizon for such would be relatively low.
The article said "well beyond the ship horizon, even when the ship is 25nm forward of the illuminator (SPG-51)".

I measured the SPY-1B on Ticonderoga to have a mean height of 19m. Therefore, a target at 10m altitude can be visible at up to 31km. Adding up the 25nm=46km claim from the article, gives us "well beyond" 77km.

You suddenly made a jump to 0.1m2? Based on targeting the BQM-74, which is an old target drone with straight wings designed in the sixties, you are suddenly assuming that is meant to simulate a Tomahawk at 0.1m2. I am not sure how you can connect the Tomahawk to 0.1m2 either given its lack of stealth features and straight wings but that's another story.
One source claimed 0.05m2 and another 0.22m2 RCS for the Tomahawk. The Tomahawk is also a significantly larger missile: it has double the frontal surface, double the length and almost four times the weight of the BQM-74.
 

Tam

Colonel
Registered Member
The article said "well beyond the ship horizon, even when the ship is 25nm forward of the illuminator (SPG-51)".

I measured the SPY-1B on Ticonderoga to have a mean height of 19m. Therefore, a target at 10m altitude can be visible at up to 31km. Adding up the 25nm=46km claim from the article, gives us "well beyond" 77km.


One source claimed 0.05m2 and another 0.22m2 RCS for the Tomahawk. The Tomahawk is also a significantly larger missile: it has double the frontal surface, double the length and almost four times the weight of the BQM-74.

That does not mean well beyond, it only means beyond.

If the object lacks RCS reduction features, its RCS isn't smaller than its physical cross section at the front. Both BQM-74 and the Tomahawk has RCS increasing features, such as the straight wings, 90 degree angle at the wing root, straight firewall behind the guidance system, straight rim where the radome connects, vertical rudder, cylindrical body and rounded head. BQM-74 was easily detected by old Iraqi radars.
 

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