J-20 5th Generation Fighter VII

latenlazy said:

Upper range capabilities don't determine lower range floors.

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They do show trends, however. Jamming antennas begin from certain sizes(to get to certain ranges and power levels), and show tendency to either grow, or pack more power in the previous size(GaN for example), or both.

Is it possible to pack weak jamming capability into comm-sized antenna?
I'd probably agree, why not. There are drone communications jammers this big.

Will it significantly affect contemporary radar? No (equations)
Does it make sense? No, point of having this system is nil, space, price and complexity is not nil. Necessary estate is in fact very limited.

Does it make sense on LO plane? x2 no, available jamming types will give a net negative survivability change, and for directional jamming - see above ...
Ultimately, rule 1 for LO plane - don't compromise your investment in LO.

Gloire_bb said:

They do show trends, however. Jamming antennas begin from certain sizes(to get to certain ranges and power levels), and show tendency to either grow, or pack more power in the previous size(GaN for example), or both.

Is it possible to pack weak jamming capability into comm-sized antenna?
I'd probably agree, why not. There are drone communications jammers this big.

Will it significantly affect contemporary radar? No (equations)
Does it make sense? No, point of having this system is nil, space, price and complexity is not nil. Necessary estate is in fact very limited.

Does it make sense on LO plane? x2 no, available jamming types will give a net negative survivability change, and for directional jamming - see above ...
Ultimately, rule 1 for LO plane - don't compromise your investment in LO.

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It’s hard to say how much the J-20 would be dependent on its radars acting as a primary jammer in an EW function when the radar has to handle multiple different tasks. It’s also not like jamming pods have honking huge antennas bigger than some of the antenna windows we see on the J-20’s surface. So once again antenna size isn’t a hard constraint on power. You can do pretty effective jamming via targeted beam steering rather than full blown saturation of the signals space. That’s how non dedicated EW platforms do their jamming functions in the first place. And targeted beam steering also happens to be how stealth aircraft can do jamming without giving themselves away to the whole environment. Not really that different from how an LPI radar function works.

Again no one is saying the J-20 can replace a growler level EW platform.

latenlazy said:

It’s hard to say how much the J-20 would be dependent on its radars acting as a primary jammer in an EW function when the radar has to handle multiple different tasks.

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That's the whole point of integtated architecture + AESA mix. Moreover, it's exactly the point where PESAs etc become hopelessly outdated - just like ESAs themselves did with mechanical scan some 20 years ago; probably even more decisively.
AESA can do all, simultaneously, through both splitting the array and polarisation. Provided you have enough processing power, of course.

Frankly speaking, that's the whole point of j-20 - together with its LO, supersonic performance, larger missiles, and connectivity.
Moreover, it's the point where it's comes first w/o doubt. Other advantages are ties with one competitor or another, this one is 'win'.

It’s also not like jamming pods have honking huge antennas bigger than some of the antenna windows we see on the J-20’s surface.

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But that's what they do. Huge - no, not yet (I see you Israel with your tricks!), but they're in fact significantly larger, often steerable, and are always placed in highly distinctive manner (b/c coverage). None match.
And we have in fact an example of 5th gen fighter with known such arrays.

You can do pretty effective jamming via targeted beam steering rather than full blown saturation of the signals space.

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But that's the problem - it's exactly that requires a powerful AESA array. You can't blind(shortsighten, slow down) ESA just by being elegant, it takes raw power, too. And this is size, more or less proportional to arrays we try to jam.

Gloire_bb said:

That's the whole point of integtated architecture + AESA mix. Moreover, it's exactly the point where PESAs etc become hopelessly outdated - just like ESAs themselves did with mechanical scan some 20 years ago; probably even more decisively.
AESA can do all, simultaneously, through both splitting the array and polarisation. Provided you have enough processing power, of course.

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You’re dividing emitter power too.

Gloire_bb said:

But that's what they do. Huge - no, not yet (I see you Israel with your tricks!), but they're in fact significantly larger, often steerable, and are always placed in highly distinctive manner (b/c coverage). None match.
And we have in fact an example of 5th gen fighter with known such arrays.

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These are not big antennas.

Gloire_bb said:

But that's the problem - it's exactly that requires a powerful AESA array. You can't blind(shortsighten, slow down) ESA just by being elegant, it takes raw power, too. And this is size, more or less proportional to arrays we try to jam.

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Jammer power is dictated by amplifier power (not antenna size!). You don’t need a large number of array elements to do effective jamming because you don’t need to match the complex waveforms of the radar you’re jamming to drown out the signal. Direct waveform cancellation is nice but really unnecessary. Simply creating enough noise to disrupt the ability for the radar receiver to untangle return signals effectively is more than enough, and what jammers are mostly configured to do.

latenlazy said:

These are not big antennas.

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(1)all things are relative - i.e. even ALQ-99(Vietnam era pod heritage!) arrays are very big compared to J-20/F-35 distributed appertures. There is simply more real estate to work with.
However, those arrays do perfectly match comms - pretty high bandwidth ones at that.

(2)Modern contemporary is NGJ, and its dedicated arrays are almost small fighter main array-sized - and steerable at that.

Jammer power is dictated by amplifier power (not antenna size!). You don’t need a large number of array elements to do effective jamming because you don’t need to match the complex waveforms of the radar you’re jamming to drown out the signal. Direct waveform cancellation is nice but really unnecessary. Simply creating enough noise to disrupt the ability for the radar receiver to untangle return signals effectively is more than enough, and what jammers are mostly configured to do.

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The problem is jamming AESAs, especially powerful ones. You need to both cover their frequency range, keep up with them on the fly, and do it with enough power to deny them butthrough.
Otherwise direct jamming will not be able to achieve neither detection/lock on delay no range dampening.

Gloire_bb said:

(1)all things are relative - i.e. even ALQ-99(Vietnam era pod heritage!) arrays are very big compared to J-20/F-35 distributed appertures. There is simply more real estate to work with.
However, those arrays do perfectly match comms - pretty high bandwidth ones at that.

2)Modern contemporary is NGJ, and its dedicated arrays are almost small fighter main array-sized - and steerable at that.

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The bumps under the wing root and the antennas on the tail boons, plus potential arrays or antennas hidden in the wing leading edge all aren’t very small. Besides the F-35 seemingly has no problem integrating dedicated EW antennas that aren’t massive. Once again, antenna size doesn’t matter here.


The jammer arrays and antennas don’t need to be NGJ sized to bring effective EW capabilities. NGJ is meant to top of the line capability. That’s not what we’re discussing here.

Gloire_bb said:

The problem is jamming AESAs, especially powerful ones. You need to both cover their frequency range, keep up with them on the fly, and do it with enough power to deny them butthrough.
Otherwise direct jamming will not be able to achieve neither detection/lock on delay no range dampening.

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Waveform interference is a lot more important than overall power if you’re trying to scramble return signals. You don’t need a total drown out of the emitter to get effective interference. Just interfere with the return signal. The receiver is an easier target than the emitter.

taxiya said:

That is only true below speed of sound where fan can accelerate air in front of it to a higher speed behind it. After the sound barrier, fan doesn't work.

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I think there's a bit of confusion here. All normal jet engines work at sub sonic speeds. While the aircraft can exceed speed of sound, the engine fan/compressor operates in the sub/transonic regime. It is the job of the engine intake (normally through a series of shock waves) to slow down the supersonic free stream so when it reaches the fan it is subsonic. Design of the intake is critical, how well it converts the speed of the free stream into a pressure increase at the compressor face (pressure recovery) directly impact performance of engine.

Generally, higher bypass better efficiency, but it achieves higher propulsive efficiency by reducing exhaust velocity. Propulsive efficiency is basically inversely proportional to exhaust velocity. However lower exhaust velocity means you can't go as fast.

Time for a new J-20 thread, here below:

J-20 5th Gen Fighter Thread VIII

New thread for J-20, as the old one was well over 700 pages. Old thread here: https://www.sinodefenceforum.com/t/j-20-5th-generation-fighter-vii.8678/page-784

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Continue discussions there