J-20 5th Gen Fighter Thread IV (Closed to posting)

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Inst

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Except that most radomes, from what I've seen, don't have the radar antenna flush with the main fuselage but instead tend to jut out into the radome area.

It could be that the material is actually reflective, like a radar dish to concentrate beams into the antenna, or alternately it limits the radome area further as the antenna cannot make use of the back area; this helps to limit RCS, but indicates that the aperture size is reduced to only 5/6ths of the apparent radome for a Flanker-sized radar.
 

Deino

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Can anyone confirm from other Chinese forums - my online-translation is a bit murky ! - that J-20 '2015' has been transferred to the CFTE at Xi'an-Yanliang this morning ???

Deino
 

gambit

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Except that most radomes, from what I've seen, don't have the radar antenna flush with the main fuselage but instead tend to jut out into the radome area.
Not fuselage, but bulkhead. Behind the bulkhead are the main avionics compartments. The antenna is mounted on the bulkhead and protrudes into the radome volume. If the antenna is the mechanical sweep type, then the sweep angle limits determines how much is that protrusion, which in turn affects antenna dimension.

f15_apg63.jpg


For the F-15 example above, do you see how the antenna is swept ? Since radome volume is conical in shape, if you want true 180deg sweep angle, the antenna will need to go deeper into that volume, which will make the antenna dimension even smaller.

It could be that the material is actually reflective, like a radar dish to concentrate beams into the antenna, or alternately it limits the radome area further as the antenna cannot make use of the back area; this helps to limit RCS, but indicates that the aperture size is reduced to only 5/6ths of the apparent radome for a Flanker-sized radar.
I tried but have no idea what this mean. Sorry.
 

Inst

Captain
Thanks for the education, Gambit.

It could be that the material is actually reflective, like a radar dish to concentrate beams into the antenna, or alternately it limits the radome area further as the antenna cannot make use of the back area; this helps to limit RCS, but indicates that the aperture size is reduced to only 5/6ths of the apparent radome for a Flanker-sized radar.

What I mean is that there is a dish behind the AESA antenna, which is the discolored part of the radome, whose role is to try to reflect and focus radar waves back onto the antenna. I don't know if this is normal, or if this is stupid from a materials engineering point of view; this is just speculation.

The second part can be easily simplified; what I mean to guess is that the Chinese just slathered RAM on the part of the radome that was unused because their radar turned out to be bulkier and smaller than expected, so it jutted more into the radome.
 

Inst

Captain
For the F-15 example above, do you see how the antenna is swept ? Since radome volume is conical in shape, if you want true 180deg sweep angle, the antenna will need to go deeper into that volume, which will make the antenna dimension even smaller.

Yes, that's believable, but the question is, why does it seem that American AESA radars occupy less of the radome's theoretical aperture area than their Russian or Chinese PESA counterparts?
 
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