AN/APG-81 Detection

Cockpit, radar, helmet-mounted display, and other avionics
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blain

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Unread post26 Apr 2019, 20:52

The AN/APG-81 is a low probability of intercept radar.

I'm thinking that the F-35 can search and track targets without being detected. I'm more familiar with mechanically scanned radar modes. Fly in search mode and then lock up a target once you decide to engage and fire. The enemy fighter detects the lock and then the fight starts.

I haven't found much information on AESA radar modes for the AN/APG-77 or 81. It seems that there is an LPI and non LPI mode. Detection ranges are less in LPI mode but the fighter receives tracking data on all targets within range. When you decide to shoot you are designating targets instead of "locking" them up. You shoot your missiles. Your fighter provides targeting updates to the missiles. At some point the missile's radar goes active and tries to acquire and shoot down the target.

When does the enemy aircraft become aware that it is being targeted? As late as the AMRAAM going active? Can some ECM systems detect the datalink between the AMRAAM and the F-22/35?
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sprstdlyscottsmn

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Unread post26 Apr 2019, 21:00

blain wrote:I haven't found much information on AESA radar modes for the AN/APG-77 or 81. It seems that there is an LPI and non LPI mode. Detection ranges are less in LPI mode but the fighter receives tracking data on all targets within range. When you decide to shoot you are designating targets instead of "locking" them up. You shoot your missiles. Your fighter provides targeting updates to the missiles. At some point the missile's radar goes active and tries to acquire and shoot down the target.

When does the enemy aircraft become aware that it is being targeted? As late as the AMRAAM going active? Can some ECM systems detect the datalink between the AMRAAM and the F-22/35?

Take this that you wrote and ignore AESA radar, LPI, APG-77, and APG-81.

You just described TWS vs PDS/STT of mechanical radars. This has been around since the early 1970s. The RWR gets a "search" blip instead of a track blip, even when a target is designated. The difference with an AESA is that it operates so "randomly" that it's TWS functions can't even be detected by an RWR that is not built to the same spec as the radar itself.
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blain

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Unread post26 Apr 2019, 21:22

sprstdlyscottsmn wrote:
blain wrote:I haven't found much information on AESA radar modes for the AN/APG-77 or 81. It seems that there is an LPI and non LPI mode. Detection ranges are less in LPI mode but the fighter receives tracking data on all targets within range. When you decide to shoot you are designating targets instead of "locking" them up. You shoot your missiles. Your fighter provides targeting updates to the missiles. At some point the missile's radar goes active and tries to acquire and shoot down the target.

When does the enemy aircraft become aware that it is being targeted? As late as the AMRAAM going active? Can some ECM systems detect the datalink between the AMRAAM and the F-22/35?

Take this that you wrote and ignore AESA radar, LPI, APG-77, and APG-81.

You just described TWS vs PDS/STT of mechanical radars. This has been around since the early 1970s. The RWR gets a "search" blip instead of a track blip, even when a target is designated. The difference with an AESA is that it operates so "randomly" that it's TWS functions can't even be detected by an RWR that is not built to the same spec as the radar itself.


So I'm thinking unless the opponent has a very good ECM system the first detection of being attacked is when the AMRAAM goes active - explaining the lopsided engagements between 4th and 5th Jen fighters.
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blain

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Unread post26 Apr 2019, 21:59

Is this accurate? Or is he applying what he knows to an AESA radar?

http://fullafterburner.weebly.com/next- ... adar-modes
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SpudmanWP

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Unread post26 Apr 2019, 22:01

Here is an early APG-81 in action.

"The early bird gets the worm but the second mouse gets the cheese."
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blain

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Unread post26 Apr 2019, 22:45

I wonder if a lot of the functions are automated, especially with the ability to fuse information from onboard sensors and other platforms - other F-35s, 4th gen fighters, ISR centric platforms.

Does the ability to tailor T/R modules to different functions such as search, track, and targeting make the previous employment of radar modes obsolete?
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marauder2048

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Unread post26 Apr 2019, 22:57

blain wrote:
When does the enemy aircraft become aware that it is being targeted? As late as the AMRAAM going active? Can some ECM systems detect the datalink between the AMRAAM and the F-22/35?



Not sure about AMRAAM specifically but some of other modern missile datalinks (e.g. P3I) use as little
power as possible and rely on error correcting codes and a downlink to ask for a re-send
if the message is uncorrectable.
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sprstdlyscottsmn

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Unread post26 Apr 2019, 23:00

blain wrote:I wonder if a lot of the functions are automated, especially with the ability to fuse information from onboard sensors and other platforms - other F-35s, 4th gen fighters, ISR centric platforms.

Does the ability to tailor T/R modules to different functions such as search, track, and targeting make the previous employment of radar modes obsolete?

yes and yes
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Unread post27 Apr 2019, 01:33

'blain' said: "I wonder if a lot of the functions are automated, especially with the ability to fuse information from onboard sensors and other platforms - other F-35s, 4th gen fighters, ISR centric platforms...." Search the F-35 forum or just this sub forum using term FUSION. There have been endless threads in the past & recently about the 'F-35 Sensor Fusion'.

Here is a start F 35 Sensor Fusion and networking: viewtopic.php?f=62&t=28922

Seems the PDF has gone missing from this post but read on: viewtopic.php?f=62&t=28922&p=319007&hilit=zoom#p319007

I've searched the forum for this article without success - it seems to be a concise overview - YMMV (apologies if posted).
F-35 Data Fusion: How the Smartest Fighter Shares What it Sees
04 Sep 2018 Nick Zazulia

"The Lockheed Martin F-35 Lightning II’s calling card is being a mobile sensor package that can the effectiveness of an entire fleet — an entire military front — by sharing data and coordinating information such that the situational awareness of every warfighter present is increased exponentially....

...The first step is the fusion engine that takes the myriad data the F-35 collects with its different sensors and combines it into a holistic picture that can be fed to the pilot — or other combatants. Lockheed Martin fellow and Information Fusion Chief Scientist Thomas Frey provided an example of the process at June’s AIAA Aviation Forum in Atlanta.

If there are 35 aircraft near an F-35, the infrared sensor might pick up all of the nearby aircraft, but has no way to tell who is friend or foe, just the direction each one is in from heat signals. The electronic warfare systems can pick up 22 of them. Six are within the Doppler radar’s field of view, giving a clear picture of those six.

The F-35 also incorporates data from air- and ground-based allies to help sort out where friends are on the battlefield. Combining the angle or range data from multiple aircraft is especially useful, as the system will automatically triangulate a target’s geolocation from multiple sources who picked it up.

Once of all of that is incorporated, the fusion engine can combine it into one picture of the battlefield that it displays to the pilot, identifying the location and distance of all 35 targets and which are foes. The autonomous sensor manager assigns a percentage to how confident it is in each of its determinations.

At the same time, it’s constantly rechecking each of those determinations and sending its data into the networks for other aircraft to be doing the same thing. One important distinction is that the final map of information it comes up with after all that combination is referred to as Tier 3 data: incorporating everything the F-35 observed as well as everything it received from allies, what Frey calls “rumors.”

What the F-35 sends out to the network is only its Tier 1 data, though, or information it has observed and measured with its own sensors. That way, each jet is only feeding the network with first-hand, reliable information so the others, and the network as a whole, can be the source of new Tier 3 data without being muddied by compounding rumor data that may or may not have been reliable....

...“For MADL, you can best think of that as a way to extend one avionics system into multiple aircraft,” said Lockheed Martin's F-35 missions systems expert, Greg Lemons. “It’s designed around a four-ship flight group to be able to exchange the data that each aircraft sees, and for each airplane to take that data and fuse that into the information for the pilot.”" [BEST READ IT ALL AT THE SOURCE - more MADL & LINK 16 info]

Source: https://www.aviationtoday.com/2018/09/0 ... ta-fusion/
A4G Skyhawk: www.faaaa.asn.au/spazsinbad-a4g/ & www.youtube.com/channel/UCwqC_s6gcCVvG7NOge3qfAQ/videos?view_as=subscriber
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Unread post27 Apr 2019, 04:45

blain wrote:
sprstdlyscottsmn wrote:
blain wrote:I haven't found much information on AESA radar modes for the AN/APG-77 or 81. It seems that there is an LPI and non LPI mode. Detection ranges are less in LPI mode but the fighter receives tracking data on all targets within range. When you decide to shoot you are designating targets instead of "locking" them up. You shoot your missiles. Your fighter provides targeting updates to the missiles. At some point the missile's radar goes active and tries to acquire and shoot down the target.

When does the enemy aircraft become aware that it is being targeted? As late as the AMRAAM going active? Can some ECM systems detect the datalink between the AMRAAM and the F-22/35?

Take this that you wrote and ignore AESA radar, LPI, APG-77, and APG-81.

You just described TWS vs PDS/STT of mechanical radars. This has been around since the early 1970s. The RWR gets a "search" blip instead of a track blip, even when a target is designated. The difference with an AESA is that it operates so "randomly" that it's TWS functions can't even be detected by an RWR that is not built to the same spec as the radar itself.


So I'm thinking unless the opponent has a very good ECM system the first detection of being attacked is when the AMRAAM goes active - explaining the lopsided engagements between 4th and 5th Jen fighters.


Take that a step further, and realize that since an AESA is effectively a giant software defined radio, the APG-81 can probably make an RWR think it is being tracked by an AMRAAM's seeker whenever it wants to. Now you get to make the enemy RWR go off constantly like it is under siege from a Macross Missile Massacre, and the bad guy effectively has no warning when the actual missile is coming.
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Unread post02 May 2019, 14:05

blain wrote:The AN/APG-81 is a low probability of intercept radar.

I'm thinking that the F-35 can search and track targets without being detected. I'm more familiar with mechanically scanned radar modes. Fly in search mode and then lock up a target once you decide to engage and fire. The enemy fighter detects the lock and then the fight starts.

I haven't found much information on AESA radar modes for the AN/APG-77 or 81. It seems that there is an LPI and non LPI mode. Detection ranges are less in LPI mode but the fighter receives tracking data on all targets within range. When you decide to shoot you are designating targets instead of "locking" them up. You shoot your missiles. Your fighter provides targeting updates to the missiles. At some point the missile's radar goes active and tries to acquire and shoot down the target.

When does the enemy aircraft become aware that it is being targeted? As late as the AMRAAM going active? Can some ECM systems detect the datalink between the AMRAAM and the F-22/35?


I really doubt there are LPI and non-LPI modes in either of those radars. LPI is actually a set of features of the radar and those features actually improve almost every performance metric, including range. Some features probably have some minor negative effect on range, but most have positive effect. Before AESA radars became available, LPI features could only be had with very low powered radars with short range. I think this is why LPI is thought to be somehow detrimental to range. Even those early LPI radars had extremely good range for the power levels they used. They used milliwatts to watts of peak output power and could match the range performance of ordinary radar using kilowatts of peak output power.

Detecting the missile uplink is definitely possible, but those use very low power and many kinds of LPI techniques in the transmission. For example the power levels can be very low as the signal only needs to go from fighter to missile. Power management is also likely used which means that initially the transmissions are low powered and power is increased when the range between fighter and missile increases. Data link beams are directed towards the missile and it's rather unlikely that there would be enemy aircraft within the beam until the missile is very close to target. I doubt normal fighter EW suites can reliabl detect modern missile data links in real life situations, especially when done using AESA radars. Maybe some dedicated high performance ESM aircraft could do it with very sensitive receivers.

AESA (and some PESA) radars usually use Scan-While-Track technique instead of Track-While-Scan used in MSA (and some, especially older or rotating PESA) radars. SWT differs in that it uses dedicated tracking beams which prioritizes target tracking and use the interim periods to search for new targets. TWS does searching all the time and target tracking is done processing the detections made during search. SWT gives much better tracking capability and quality. Targets will not know the difference between those two modes as those tracking beams are just like search beams.

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