PLAN Anti-ship/surface missiles

nlalyst said:

Don't forget that we are discussing the Type 517M radar here, not the Nebo-M. The former has just 4 antennas in a row, while the Nebo-M has 22 antennas. The Nebo-M is credited with an impressive 0.5 degree accuracy, although it is unclear exactly how it achieves this as its mainlobe beam is going to be around 5 degrees wide. If it uses monopulse, then its power-aperture will drop to 25% significantly impairing its detection range. But for the sake of argument, let's assume that's still sufficient to detect the LRASM at 30km range. Scaling to 517M, azimuth accuracy will be 22/4 * 0.5 = 2.75 degrees. Can you redo your calculation with this figure?

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The number and size of antennas should just affect the total power output, number of beams and 3D tracking.
I don't see how it should affect the angular accuracy of each individual beam in the vertical plane.

nlalyst said:

How did you get 7 degrees? In you example above, if the error is 838m doesn't that mean that you should draw a circle of radius 838m, as the area of uncertainty?

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Yes, the LRASM could be anywhere in a circle with a radius of 419m. But since you know it is a sea skimmer, I'm assuming a line across the horizon.

nlalyst said:

It would help if you specify the speed that you used for HHQ-9. Given the short range of the engagement, it will likely be close to its top speed: 2000 m/s?

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Mach 4.2 as listed.

nlalyst said:

No, you can't do that. First you need to figure out what it is that you detected. That's called an OODA loop.

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It's a simplified assumption assuming zero time required.
But by all means, go ahead and add some OODA loop.
You still end up with 3-4 engagements before the 13km engagement start on CMO.

nlalyst said:

When you redo your calculations, don't forget to take into account that the Type 517M is a rotating radar and that your signal updates are some 6s apart. In those 6s, a maneuvering LRASM can cover at least 1,5-1,8km.

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The simplest thing would be to make the VHF radar directional for terminal tracking, like we see with the E-2D
It's a software change after all.

nlalyst said:

@AndrewS
One more thing: Type 517 is a 2D radar. It can't tell you the altitude of the target.

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Do you really need to the know the exact height of a sea skimming missile? We're literally talking about <10metres

AndrewS said:

The number and size of antennas should just affect the total power output, number of beams and 3D tracking.
I don't see how it should affect the angular accuracy of each individual beam in the vertical plane.

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The Nebo-M is an AESA radar. In AESA radars, the beamwidth per axis is inversely proportional to the number of elements along that axis.

The Knife Rest radar, in design very similar to the Type 517, had a beamwidth of 21 degrees:

AndrewS said:

Yes, the LRASM could be anywhere in a circle with a radius of 419m. But since you know it is a sea skimmer, I'm assuming a line across the horizon.

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Think about it: if the error is 100m, that means it can be a 100m off to the left, a 100m, off to the right, a 100m off to the top, etc.

AndrewS said:

Do you really need to the know the exact height of a sea skimming missile? We're literally talking about <10metres

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If you have a 2D radar, how would you know it is a sea skimming missile? It could just as well be cruising at 15km.

nlalyst said:

The Nebo-M is an AESA radar. In AESA radars, the beamwidth per axis is inversely proportional to the number of elements along that axis.

The Knife Rest radar, in design very similar to the Type 517, had a beamwidth of 21 degrees:

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Think about it: if the error is 100m, that means it can be a 100m off to the left, a 100m, off to the right, a 100m off to the top, etc.


If you have a 2D radar, how would you know it is a sea skimming missile? It could just as well be cruising at 15km.

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For the last, if you got a Yagi antenna, signal strength is strongest on bore sight with the antenna. As the signal goes off bore, it gradually diminishes.

With two Yagi antenna sets one above the other, if the object is high, the higher Yagi gets a stronger signal relative to the lower Yagi. If the object is lower, the lower Yagi gets a stronger signal strength than the higher Yagi. Only if the object is equidistant in height between the two Yagi, are the signal strength on the two Yagi equal.

With four Yagi, you are measuring signal strength across the Yagi in both X and Y axis. Higher and lower Yagi for the height, left and right Yagi for the azimuth.

The strength of the signal can tell you from what direction the signal is coming from relative to the bore sight of the Yagi. From this its possible to form a line that traces to the source. But the signal to Yagi A will be different to Yagi B, Yagi C and Yagi D. Each will have a different bearing to the source. From where all these lines would intersect, this is where the source is. Based on the return echo you can get the range, and from there on the height of the source.

With the new "Fly Swatter" array, they use loop antennas instead of Yagi. Loops have higher gain than Yagis, but they work the opposite, with boresight being null and strongest at the sides. Would be interesting to see the research papers behind this.

For other 2D radars, the ones like you see that have an oval parabolic dish, they use a different technique call height multipathing. This one is more relevant to radars like the Type 364.

nlalyst said:

The Nebo-M is an AESA radar. In AESA radars, the beamwidth per axis is inversely proportional to the number of elements along that axis.

The Knife Rest radar, in design very similar to the Type 517, had a beamwidth of 21 degrees:

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At the end of the day, the official specification list for the Type-517 says <1%.
That is worst than the larger NEBO which is listed as <0.5%
So it sounds credible.

Plus you're grasping when you compare against a 1950s era P-10 radar
For one thing, we now have very accurate digital clocks and computers which reduces errors tremendously.
Back then they were relying on tubes and had zero compute power.

nlalyst said:

Think about it: if the error is 100m, that means it can be a 100m off to the left, a 100m, off to the right, a 100m off to the top, etc.

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That 200m error is within the tolerances of the SAM X-Band radar and the missile kinematics.

AndrewS said:

At the end of the day, the official specification list for the Type-517 says <1%.
That is worst than the larger NEBO which is listed as <0.5%
So it sounds credible.

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It doesn't sound credible. The only "specification" I saw was on Wikipedia. Find me a similarly configured VHF radar that has less than <1 degree accuracy.

The Type 517 is a 2D radar. Its search beam is probably over 10 degrees wide. It rotates at a slow update rate. It's practically useless as a target acquisition radar. But that's understandable, since it's an early warning radar after-all.

nlalyst said:

It doesn't sound credible. The only "specification" I saw was on Wikipedia. Find me a similarly configured VHF radar that has less than <1 degree accuracy.

The Type 517 is a 2D radar. Its search beam is probably over 10 degrees wide. It rotates at a slow update rate. It's practically useless as a target acquisition radar. But that's understandable, since it's an early warning radar after-all.

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And the wikipedia page takes you to the manufacturer's page with the sales specification with an angular error of <1%

Plus reprogramming the radar to have a targeting mode is a software update.

AndrewS said:

And the wikipedia page takes you to the manufacturer's page with the sales specification with an angular error of <1%

Plus reprogramming the radar to have a targeting mode is a software update.

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All i found was a photo of a power point slide. The beam-width is particularly unconvincing. A much larger P-18 radar has a beamwidth of 6 degrees:

You cannot magically convert a 2D early warning radar into a targeting radar through a software update.

AndrewS said:

If the HQ-9B has an Active Radar Seeker, logically it has to be able to receive mid-course guidance.

It's interesting to note that swarms of LRASMs don't currently exist.
LRASM has only recently been introduced, so only about 100 exist today.
And the plan is to only buy 48 LRASMs per year, until hypersonic missiles are ready.

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There is a stock in 4 digits as of now, they bought upper hundreds for several years.
Current small-batch purchases are basically a sustainer.

Are you guys talking about the same LRASM as mentioned here?

contract volumes for various fiscal years throughout its lifetime so far are not very high at all.