PLA AEW&C, SIGINT, EW and MPA thread


tphuang

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a new KJ-2000 caught on photo B-4041

I suspect there is also a B-4042
giving us the original #762 and then B-4040-4043
or maybe the original one got repainted.
 

Totoro

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So just how are we to know if planes do get repainted and renumbered or not? Theoretically, there could be as many as five kj2000, right? But what if not only the first one, #762 got renumbered but what if plaaf is purposefully repainting same two planes with B-40xx system? There's certainly a valid reason why they might want to try to do it if they have hangars large enough to accept multiple kj2000 which would then prove it impossible for US satellite recon to determine just how many are there. Not to mention that satellites are tracked and their coverage is far from 24/7, even for a small area.
 

tphuang

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Totoro said:
So just how are we to know if planes do get repainted and renumbered or not? Theoretically, there could be as many as five kj2000, right? But what if not only the first one, #762 got renumbered but what if plaaf is purposefully repainting same two planes with B-40xx system? There's certainly a valid reason why they might want to try to do it if they have hangars large enough to accept multiple kj2000 which would then prove it impossible for US satellite recon to determine just how many are there. Not to mention that satellites are tracked and their coverage is far from 24/7, even for a small area.
I guess the one way would be to compare the photos. Actually, I personally can't tell the difference between the KJ-2000 modified from A-50 and IL-76, but someone with a good set of eyes probably can.

As for 4 plane, this is something that I read on the Chinese forum from a guy called "spoiler dude" or something like that. He has quite a good reputation there. Basically, he said that there are 4 KJ-2000 joining service at the end of 2005 (following the original Phalcon plan I guess).
 

duskylim

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Dear TP:

Great new pic! Hopefully there will be more to come. BTW IIRC there were previous posts of the hangers for the KJ-2000 series where several aircraft were seen parked together...

As for the disk configuration of the rotodome, in the original Boeing Sentry (E-3 series) there is a large slotted planar array that is rotated slowly (at about 6 revs/min) by a hydraulic unit.

The array consists of a series of rectangular section beams that are stacked one on top of the other and are fed from waveguides. The longest beams are in the center of the array, with progressively shorter beams stacked above and below as you move away from the middle.

The rotodome itself is basically an aerodynamic fairing to cover the large slotted array. So its like a giant (albeit extremely flat oval-shaped) planar type slotted array antenna. Like what you would see in a typical fighter except of course much bigger and much more powerful.

The beam can be electronically steered through a limited angle although it relies on hydraulics to perform a 360 degree scan.

The KJ-2000 system stacks 3 shorter phased arrays in an equilateral triangle configuration with electronic beam steering. This eliminates the need to rotate the antenna assemble to scan.

The technology of the phased array allows for this. Because it relies on phase shifting, there is no output at an electronic scan of 90 degrees - the crests and troughs of the waves simply cancel out! The effective scan angle is about 60 degrees away from the perpendicular.

Hope this helps,

Best Regards,

Dusky Lim
 

Totoro

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almost all articles on esa i've read concur that there's visible degradation beyond 45 degrees from the axis, with 60 degrees being maximum that's useful, anything beyond makes the range/resolution drop very sharply. So question might be - why not put 4 arrays each covering the ideal 90 deg arc, instead of 3 arrays each covering 120 deg? Could it be that the price/weight/power usage is that much greater?

arj21 would make a very good (if not excellent! :D) awacs platform. (any not just awacs platform but that's another story) IF non US engines can be installed, as there's no way US would let GE engines on military version. I wonder if it'd be viable to go for russian ps-90 high bypass turbofan series, especially if they're already being used on il76. Anyone have that info? are the upcoming 30 il76 gonna be using d30kp like older il76 china has or are they gonna be using ps90a-76?
 

crobato

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If you have four arrays on a square, than three arrays in a triangle, guess what, measure the length of each array. You will notice it's shorter. A shorter array would mean less reception range. Ergo, lower detection ranges as a result.
 

Totoro

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Range would be lower beyond 45 deg off axis anyway. It's all nice and dandy, but i wish we had some equations showing just how much does high off bore angle beam steering does influence range, as well as how much range is gained by longer array area. I guess we can try interpolating from other radars but for that we'd need to know their power and clutter processing abilities. So one can compare benefits with costs. I guess plaaf concluded true 360 deg coverage is just not as important, seeing how kj200 lacks it and even kj2000 doest give same range across 360 deg view.
 

crobato

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That's because you can always fly and adjust your direction to put the target right into the radar's sweet spot. These planes do not travel in a straight line, you know.
 

Totoro

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I am not saying benefits of kj2000 array don't outweigh the costs, maybe they do. I was just observing the difference in logic between various awacs systems. I guess it will be interesting to see what logic will next gen US awacs use, when it gets a true ESA array.

also, a plane will always have to make some turns, it can't afford to position itself so target is in radar's sweet spot and just keep going on like that. There's a reason why awacs planes usually fly in 8 shaped paths. So with lack of 360 coverage one might have good coverage 95% of the time but there's always that bit while turning compromises the coverage. Granted, in practical real world terms it's very hard to take significant advantage of that but theoretically it's still possible. :D
 

tphuang

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Totoro said:
I am not saying benefits of kj2000 array don't outweigh the costs, maybe they do. I was just observing the difference in logic between various awacs systems. I guess it will be interesting to see what logic will next gen US awacs use, when it gets a true ESA array.

also, a plane will always have to make some turns, it can't afford to position itself so target is in radar's sweet spot and just keep going on like that. There's a reason why awacs planes usually fly in 8 shaped paths. So with lack of 360 coverage one might have good coverage 95% of the time but there's always that bit while turning compromises the coverage. Granted, in practical real world terms it's very hard to take significant advantage of that but theoretically it's still possible. :D
didn't we see a photo a while back, where the radome turned slightly? That could possibly cover some weak spots.
 

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