Stealth, Radars and Discussions on 5th Generation Technology

p2prada

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The term 'smart skin' have been thrown around quite carelessly. No idea on how is it supposed to be 'smart'. No idea on which character of the radar pulse is this 'smart skin' supposed to act against. The more I read about it the more skeptical I become about it. It is not just about countering phase array systems, if I can successfully negate the capabilities of a phase array system, I can easily negate lesser capable radar systems out there.
I don't mean this will make an aircraft more stealthy by negating the enemy radar waves. When I say smart skin I mean sensors embedded under the skin of the aircraft, these are positioned in such a way so as to defeat the LPI of an AESA. These sensors are receivers and will tune into any beam falling on it. In other words, this is a radar warning receiver, RWR.

What I mean is will such a high degree of awareness render existing systems, including AESA Obsolete??
 

gambit

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I don't mean this will make an aircraft more stealthy by negating the enemy radar waves. When I say smart skin I mean sensors embedded under the skin of the aircraft, these are positioned in such a way so as to defeat the LPI of an AESA. These sensors are receivers and will tune into any beam falling on it. In other words, this is a radar warning receiver, RWR.

What I mean is will such a high degree of awareness render existing systems, including AESA Obsolete??
Low Probability of Intercept (LPI) is a more a mode of operation than a distinct radar type, although there are some hardware involve. The word 'intercept' here mean that the signal is recognized by the radar warning receiver system (RWR) as a scanning transmitted signal and not as noise or a spike above the clutter region.

If we look at a typical spectrum analyzer scope there will be a constant background noise, or 'hiss' if this is converted to an audio signal. In LPI mode, and we will assume the LPI transmitter to be an 'aggressor' type, the aggressor transmitter will transmit a pulse that is either with the same signal strength as this background radiation (hiss) or just a spike above it. The victim usually does not know the specific frequency the aggressor will employ at any time. That is why RWR sets are usually broadband. Even if the aggressor signal spiked above background noise, unless there is a sequence of pulses with the same characteristics from pulse to pulse, the RWR set will dismiss this spike as nothing more than an anomaly, which by itself is nothing unusual. Spikes happens often.

For the aggressor, one pulse is not enough to acquire any significant information about the target. But if the aggressor transmit another pulse with the exact same pulse signature as before, then the RWR could recognize it as an attempt to acquire information, hence the word 'intercept'. So instead of transmitting another pulse with the same pulse signature, the aggressor will transmit a pulse with slightly different characteristics, such as a different freq or amplitude or phase. As long as the aggressor remember what was employed when, it will be able to mislead the victim into believing that no one is attempting to scan it, hence the phrasing 'low probability'.

The downside to this approach, for the aggressor, is that because the signal strength is so low, either within clutter region or just slightly above it, any target information require multiple attempts of verification. Pulse energy do get lost in transit, the longer the transit time, the less energy arrive at the target and even less energy that bounced off that target. This is called 'atmospheric attenuation'. Most of the 'stuff' that sap the pulse's energy is simple moisture, next is microscopic dust.

But there is a capability that is unique to the AESA system that no PESA can do -- subarray partitioning.



Essentially, what subarray partitioning does is to create several smaller AESA beams from the main AESA antenna assembly. It is a software based feature. In the image above, ( a ) is one beam and ( c ) has nine distinct beams. See that? You can count the other two configurations for yourself.

This is what make an AESA so dangerous for the victim. In LPI mode, the aggressor can transmit nine simultaneous pulses with each pulse different in signature than the others. A couple or more pulses may spike above background noise level to provide the aggressor confirmation of target presence and basic characteristics. The rest will provide tracking information. Or instead of all nine subarrays against the victim, still in LPI mode, the aggressor may use only four subarrays against a victim, three in volume search just in case the victim has companions, one subarray standing by to act as a jammer, and the last subarray act as a secure data link.

The victim may have 'smart skin' but all that does is to give him improved coverage over blade antennas that is typical of RWR systems today.

This is what an F-16 RWR antenna set look like...

Randtron Antenna Systems RWR Antennas

Install more blade antennas and it would accomplish the same thing as the 'smart skin' but at the expense of increased drag. So really the 'smart skin' benefits lies more in aerodynamics than from certainty of interception of aggressor radar signals. Even the classical concave dish or slotted planar array can perform LPI functions. All the aggressor has to do is fix the antenna in the direction of the target, assuming the victim's presence is established, and transmit away. As long as the pulses are sufficiently different from one another and remains largely within the clutter region, it will be difficult for the victim to confirm attempts at detection and take defensive measures.
 

AJSINGH

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That barely makes sense, again.
what is it you dont get
i said that there is systems onboard F-35 which is know as C4ISR that give f-35 battlefield awarness such as incomming hostile missile ,and where friend and foe are present .
 

p2prada

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If we look at a typical spectrum analyzer scope there will be a constant background noise, or 'hiss' if this is converted to an audio signal. In LPI mode, and we will assume the LPI transmitter to be an 'aggressor' type, the aggressor transmitter will transmit a pulse that is either with the same signal strength as this background radiation (hiss) or just a spike above it. The victim usually does not know the specific frequency the aggressor will employ at any time. That is why RWR sets are usually broadband. Even if the aggressor signal spiked above background noise, unless there is a sequence of pulses with the same characteristics from pulse to pulse, the RWR set will dismiss this spike as nothing more than an anomaly, which by itself is nothing unusual. Spikes happens often.
The hiss can be heard when we tune into the radio too.

For the aggressor, one pulse is not enough to acquire any significant information about the target. But if the aggressor transmit another pulse with the exact same pulse signature as before, then the RWR could recognize it as an attempt to acquire information, hence the word 'intercept'. So instead of transmitting another pulse with the same pulse signature, the aggressor will transmit a pulse with slightly different characteristics, such as a different freq or amplitude or phase. As long as the aggressor remember what was employed when, it will be able to mislead the victim into believing that no one is attempting to scan it, hence the phrasing 'low probability'.
And that is handled by frequency hopping etc, or in layman terms ECCM.

But there is a capability that is unique to the AESA system that no PESA can do -- subarray partitioning.



Essentially, what subarray partitioning does is to create several smaller AESA beams from the main AESA antenna assembly. It is a software based feature. In the image above, ( a ) is one beam and ( c ) has nine distinct beams. See that? You can count the other two configurations for yourself.


With a large number of T/R modules, the partitioning will far exceed 9. And if the requirement is to track 64 targets at once, then how many such partitions do you expect an AESA to have?
 

p2prada

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what is it you dont get
i said that there is systems onboard F-35 which is know as C4ISR that give f-35 battlefield awarness such as incomming hostile missile ,and where friend and foe are present .
Your answer can be given to a politician and not to a technician.

It's like going to a doctor cause you are sick and he tells you you are sick without any other information. Get my point.

EDIT: There is no system called C4ISR. It is just a term which stands for Command, Control, Communication, Computer, Intelligence, Surveillance, and Reconnaissance.
 

AJSINGH

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Your answer can be given to a politician and not to a technician.

It's like going to a doctor cause you are sick and he tells you you are sick without any other information. Get my point.

EDIT: There is no system called C4ISR. It is just a term which stands for Command, Control, Communication, Computer, Intelligence, Surveillance, and Reconnaissance.
thank you for pointing it out . yeh i did not read what i was writing but i found what you are looking for now
F-35 Distributed Aperture System (EO DAS)
Northrop Grumman has developed the only 360 degree, spherical situational awareness system in the electro-optical distributed aperture system (DAS). The DAS surrounds the aircraft with a protective sphere of situational awareness. It warns the pilot of incoming aircraft and missile threats as well as providing day/night vision, fire control capability and precision tracking of wingmen/friendly aircraft for tactical maneuvering.

Designated the AN/AAQ-37, and comprising six electro-optical sensors, the full EO DAS will enhance the F-35's survivability and operational effectiveness by warning the pilot of incoming aircraft and missile threats, providing day/night vision and supporting the navigation function of the F-35's forward-looking infrared sensor.

The DAS provides:

Missile detection and tracking
Launch point detection
Situational awareness IRST & cueing
Weapons support
Day/night navigation
In addition to developing the EO DAS, Northrop Grumman Electronic Systems is supplying the F-35's AN/APG-81 advanced electronically scanned array (AESA) fire-control radar. The AESA radar is designed to enable the pilot to effectively engage air and ground targets at long range, while also providing outstanding situational awareness.
here is the link to the website
F-35 Distributed Aperture System (EO DAS)
 

p2prada

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thank you for pointing it out . yeh i did not read what i was writing but i found what you are looking for now
F-35 Distributed Aperture System (EO DAS)
Northrop Grumman has developed the only 360 degree, spherical situational awareness system in the electro-optical distributed aperture system (DAS). The DAS surrounds the aircraft with a protective sphere of situational awareness. It warns the pilot of incoming aircraft and missile threats as well as providing day/night vision, fire control capability and precision tracking of wingmen/friendly aircraft for tactical maneuvering.

Designated the AN/AAQ-37, and comprising six electro-optical sensors, the full EO DAS will enhance the F-35's survivability and operational effectiveness by warning the pilot of incoming aircraft and missile threats, providing day/night vision and supporting the navigation function of the F-35's forward-looking infrared sensor.

The DAS provides:

Missile detection and tracking
Launch point detection
Situational awareness IRST & cueing
Weapons support
Day/night navigation
In addition to developing the EO DAS, Northrop Grumman Electronic Systems is supplying the F-35's AN/APG-81 advanced electronically scanned array (AESA) fire-control radar. The AESA radar is designed to enable the pilot to effectively engage air and ground targets at long range, while also providing outstanding situational awareness.
here is the link to the website
F-35 Distributed Aperture System (EO DAS)
Thank You. But, this wasn't the answer I was looking for. Gambit has already answered my question.
 

ppgj

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@gambit sir
am asking this in a strictly american context.
in the light of AESA radars funtioning as jammers, are the exclusive jamming pods like ALQ-99 will become redundant in a forseeable future?
power may be an issue for now. but as better engines come out and their output keeps going up,will they be able to power the AESAs to the extent they can act as active jammers also?
AESAs themselves as time goes on in research will start using less power compared to their consumption as of now.
 

gambit

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So now you have an idea of the versatility of an AESA system and why it is the default 'want' of every military.

With a large number of T/R modules, the partitioning will far exceed 9. And if the requirement is to track 64 targets at once, then how many such partitions do you expect an AESA to have?
Your question is best answered by understanding how the classical radar systems work in dealing with multiple targets.

As the antenna mechanically sweeps in volume search mode, if it detect any return, the system will remember the approximate locations of those returns. On the next sweep back, keep in mind that the antenna is sweeping back and forth, the system will momentarily change freqs at those locations. Higher freqs equal to improved target resolutions. Then as the antenna move away from those positions, the system switches back to volume search freqs again. The process is so fast that it give the impression that the system is doing several things at once. But it is a false or pseudo-multitasking capability.

With subarray partitioning in an AESA system, we have a true multi-tasker available. Keep in mind that there is a difference between antenna and array, the antenna contain the array. Say we divide the main array into two subarrays. We can have one subarray continue to perform nothing but volume search in the entire area in front of us and the other subarray does nothing but extremely fast switch its main beam from one target to the next. Because the two arrays are operating at different freqs, they will not interfere with each other. Neither subarray is multi-tasking, not even the array that is tracking multiple targets since all it does is move its main beam from one target to the next.

But what if the many targets are widely spread out? We can assign one subarray to one sector and the other subarray to the other sector, each performing that pseudo-multitasking of switching between volume search and target tracking. The advantage with a phase array system, PESA or AESA, is that because of the extremely fast beam movement, this pseudo-multitasking capability is much faster than with the classical mechanically motivated antenna. The downside with subarray partitioning is that because array size is proportionate to power output, the more subarrays we create, the less power output per array. The sum of all individual subarrays equal to original power output when the antenna was one array, of course.

With a PESA system, we remove the motors that move the antenna and move the single main beam, extremely fast, of course. With an AESA system, not only did we removed the motors, with subarray partitioning, we have multiple main beams to do as we please. The Russians installed motors with their ESA systems. That is not a bad idea. It give the system additional coverage thru mechanical mean. But with any mechanical system, there is an increased risk of lock-ups, stress, etc...etc...Take your chances.

There is no definitive figure to your question as the hypothetical situation of tracking 64 targets depends on the quality of the array choreography program, which cannot place any demands that exceed the quality of the hardware, which contains the T/R elements and how they were manufactured, the packaging of the related computers, the power supply, the shielding, etc...etc...

There are many strategies in writing array choreography programs. Each has advantages and disadvantages. We cannot demand the pilot to pick them out. He will be busy fighting for his life and for the greatest need of the conflict -- win the war. For example...Say we demand the pilot to create two subarrays, one for volume search and one to track 10 targets. But the nature of air combat is that nothing is static, not even the slow moving weather balloons and winds can carry them at a couple hundreds km/h, so what if 5 targets move beyond the scan limit of the tracking subarray? Do we program the system to automatically switch the two subarrays into pseudo-multitasking to keep track of all 10 targets? Or do tell the pilot to throw a switch or two to make it so? If you can imagine the arguments, pro and con, automatic or manual, JUST FOR YOURSELF, now see how difficult it can be when many people have their own opinions just on how to deal with 10 targets with two subarrays while the system itself is capable of being far more than two subarrays.

Subarray partitioning and array choreography softwares are cans of worms, from technical issues to combat tactics, that have created a lot of animosities between people across many disciplines. It is wise to have a critical mind when coming across claims of accomplishments or capabilities from any manufacturor, even from US, or especially from the Russians and the Chinese.

:coffee_spray:
 

gambit

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@gambit sir
am asking this in a strictly american context.
in the light of AESA radars funtioning as jammers, are the exclusive jamming pods like ALQ-99 will become redundant in a forseeable future?
power may be an issue for now. but as better engines come out and their output keeps going up,will they be able to power the AESAs to the extent they can act as active jammers also?
AESAs themselves as time goes on in research will start using less power compared to their consumption as of now.
No...Dedicated ECM systems like jamming pods will not be obsoleted by the ECM capability of an AESA system. At least I do not see such obsolescent within the next decade. When an AESA array, main or sub, perform an ECM function, it is largely directional, so power supply is not an issue, but because the array, no matter its function, directly affect power output, then the smaller the array, the less the power output. A larger power supply simply a greater reserve. ECM pods have greater coverage area when needed so for them power supply or reserve is crucial. Of course, when conformal AESA arrays are installed, meaning we have mastered their use beyond the current planar configuration, then may be the time for ECM pods will be over.
 

A.V.

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A must read before debating on j-20 stealth features ........
 

A.V.

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For those who talk about stealth technology without understanding please refer to this thread for knowledge :-----

BUMPED
 

ersakthivel

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So there may be ways to intercept stealth fighters in future. that makes the playing field level and focuses things back to aerodynamics, and good old number game with cost effective fighter platforms.
 
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power_monger

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America has choosen to invest too much into Steal technologies. They have taken a high risk by going by single strength point of stealth in F-35. With advancements in signal processing every passing year, i think this is a dangerous strategy.
 

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