APG-77 development and features

[viperzerof-2]

IEEE paper on the development of the APG-77 and some of its features. I’m not aware of this being common knowledge. Hope it’s interesting.

[hornetfinn]

Very, very interesting to read viperzerof-2, thank you!

There are a lot of very interesting tidbits in this document. For example:

In the area of survivability, the APG-77’s antenna design supports the F-22’s stealthy RCS thus reducing the enemy’s ability to detect and track the F-22. Low probability of intercept (LPI) techniques have been incorporated into all aspects of the radar functional waveform design limiting the ability of the threat systems to identify and exploit F-22 emissions, Low RCS and LPI implementations give the pilot increased survivability supporting the “First Look” advantage.

So there is no dedicated LPI modes as often claimed, but the radar is LPI design in every way.

The electronically scanning antenna configuration options were grouped into the active and passive categories. Both types of concepts were evaluated and aircraft constraints such as volume, weight, & prime power were defined for each within the context of the fixed long range detection requirements. At the higher detection ranges required in the F-22, the active electronically scanning array (ESA) configuration required significantly less volume, weight and prime power. The passive ESA configuration exceeded air vehicle volume and prime power allocations and nearly doubled the weight achievable in the active ESA design. Cost estimates for both were comparable but the active ESA involved higher risk in producibility while in general
achieved the target detection range performance within the F-22 platform constraints. Additional benefits in the active ESA were identified in the area of wider transmit bandwidth and in the “graceful” degradation to performance offered with faled individual modules versus the traveling wave tube single failure possibility in the passive design.

F-22 with PESA would've been interesting but quite a bit less capable. Good thing that AESA design was chosen.

[hornetfinn]

I also think that this paragraph about future trends are rather interesting although not very surprising:

The trend for future avionics systems is toward more capability in less space. Receiver functionality will continue to progress toward the aperture level with the first down convert at the array being the next likely step. Extremely stable crystal technology will be needed to support small target detection requirements anticipated in the future. Low volume, efficient power supplies will be in demand to support high fidelity power requirements in advanced low noise avionics systems. High density distributed power supply approaches are likely applications at the array level with each array subunit powered by it’s own power supply. “Tile” architecture based antenna designs will move the ESA technology away from the “brick” approach used in the F-22 design toward innovative ESA approaches which will be needed to support “thinner”, more conformal arrays, Smarter array designs will be required to support “self healing” features which extend the mamtenance free life of the active array. Aperture and radome integration will require continued attention in order to bring the arrays closer to the inner mold line of the aircraft. Conformal multifaceted aperture technology will continue to advance in order to meet increased field of regard requirements brought on by integrated EWhadar systems. Combined system approaches will bring electronic warfare and radar systems under one system hardware configuration pushing bandwidth limits in microwave components and apertures.

[charlielima223]

Thanks for the read viper. It didnt make too much sense to my knuckle dragger brain but I pretty much got the gist of it after I read a few parts a couple times over.

Very, very interesting to read viperzerof-2, thank you!

There are a lot of very interesting tidbits in this document. For example:

In the area of survivability, the APG-77’s antenna design supports the F-22’s stealthy RCS thus reducing the enemy’s ability to detect and track the F-22. Low probability of intercept (LPI) techniques have been incorporated into all aspects of the radar functional waveform design limiting the ability of the threat systems to identify and exploit F-22 emissions, Low RCS and LPI implementations give the pilot increased survivability supporting the “First Look” advantage.

So there is no dedicated LPI modes as often claimed, but the radar is LPI design in every way.

The electronically scanning antenna configuration options were grouped into the active and passive categories. Both types of concepts were evaluated and aircraft constraints such as volume, weight, & prime power were defined for each within the context of the fixed long range detection requirements. At the higher detection ranges required in the F-22, the active electronically scanning array (ESA) configuration required significantly less volume, weight and prime power. The passive ESA configuration exceeded air vehicle volume and prime power allocations and nearly doubled the weight achievable in the active ESA design. Cost estimates for both were comparable but the active ESA involved higher risk in producibility while in general
achieved the target detection range performance within the F-22 platform constraints. Additional benefits in the active ESA were identified in the area of wider transmit bandwidth and in the “graceful” degradation to performance offered with faled individual modules versus the traveling wave tube single failure possibility in the passive design.

F-22 with PESA would've been interesting but quite a bit less capable. Good thing that AESA design was chosen.

Sounds like in order for the PESA to have the same amount of capability/performance as the AESA would require a larger radar. I've always made a SWAG that this is the reason why modern Russian Flankers require such a physically large radar.

[hornetfinn]

Sounds like in order for the PESA to have the same amount of capability/performance as the AESA would require a larger radar. I've always made a SWAG that this is the reason why modern Russian Flankers require such a physically large radar.

Yes and that's only to have equal detection range using 1990's technology and AESA technology has improved tremendously since then. PESA radars today are better than they were 20-30 years ago but that's nothing compared to how much AESA technology has improved. Of course AESA tech had other significant advantages over PESA technology even then. They had much better LPI capabilities through much wider bandwidth, higher duty cycle, better power management, better frequency agility and capability to use several simultaneous beams. They also had multi-role capabilities like use as ESM/EW antenna or data link antenna. So it offered better RF stealth and non-radar capabilities. Nowadays the difference in these areas is even bigger with latest technology.

I think you are correct about Russian Flankers. N011M Bars radar in Su-30 weighs something like 650 kg (1431 lbs) whereas AN/APG-77 weighs 524 lbs (or 238 kg)... That's ridiculous difference. Irbis-E is lighter than Bars but still very heavy in comparison to APG-77. Of course PESA radar using Western/US technology would've likely been significantly smaller/lighter but still far more than using AESA technology. According to French Wikipedia and other French sources I could find, RBE2 PESA in earlier Rafales weighs about 270 kg... So even it is heavier than AN/APG-77. Of course there might be some differences in calculating weighs but I think it's safe to say that AN/APG-77 is very light radar. Of course not having traditional back-end also helps it compared to more traditional configurations.

[viperzerof-2]

Sounds like in order for the PESA to have the same amount of capability/performance as the AESA would require a larger radar. I've always made a SWAG that this is the reason why modern Russian Flankers require such a physically large radar.

Yes and that's only to have equal detection range using 1990's technology and AESA technology has improved tremendously since then. PESA radars today are better than they were 20-30 years ago but that's nothing compared to how much AESA technology has improved. Of course AESA tech had other significant advantages over PESA technology even then. They had much better LPI capabilities through much wider bandwidth, higher duty cycle, better power management, better frequency agility and capability to use several simultaneous beams. They also had multi-role capabilities like use as ESM/EW antenna or data link antenna. So it offered better RF stealth and non-radar capabilities. Nowadays the difference in these areas is even bigger with latest technology.

I think you are correct about Russian Flankers. N011M Bars radar in Su-30 weighs something like 650 kg (1431 lbs) whereas AN/APG-77 weighs 524 lbs (or 238 kg)... That's ridiculous difference. Irbis-E is lighter than Bars but still very heavy in comparison to APG-77. Of course PESA radar using Western/US technology would've likely been significantly smaller/lighter but still far more than using AESA technology. According to French Wikipedia and other French sources I could find, RBE2 PESA in earlier Rafales weighs about 270 kg... So even it is heavier than AN/APG-77. Of course there might be some differences in calculating weighs but I think it's safe to say that AN/APG-77 is very light radar. Of course not having traditional back-end also helps it compared to more traditional configurations.

RBE2 is a bit heavier then RDY 240kg but much heavier then J/APG-1 150kg which is roughly in the same class and actually three years older. RBE2 AESA which apparently maintains the backend modes and scan algorithms of the PESA weighs 290kg go figure.

[Scorpion82]

Intersting for me is the lack of dedicated Aircombat Modes (ACM). The radar will probably adapt search and track i.a.w. the Tactical Globe concept, i.e. selection of the gun or a Sidewinder may automatically optimise the search and target tracking logic to fit the weapon envelope. The fine thing about ESA radars is that they can scan pretty fast, covering a large area. The even finer thing about an AESA is that it can continueously track a target, while doing other things in parallel thanks to multiple beam forming.

Concerning the PESA the study already states that a PESA design would have weighed twice as much. On a design like Bars, or Irbis you have to take into account the sheer size of the antenna, as well as the mechanical gimbal included in the design for FoR extension and performance improvement over a wider range of angles by keeping the antenna pointed, at least more closely, to where the target is compared to fixed antenna designs. For that reason the F-22 was designed with cheek array provisions in mind. Others are approaching the problem with mechanical devices to point the AESA antenna (Captor-E or ES-05A Raven).

In a PESA configuration you still need the traditional TWT based transmitter, wave guides. These LRIs account a lot for the space consumption and weight compared to an AESA solution which essentially consists of a power supply, antenna, receiver and processor only. You may partition the equipment differently though.

[disconnectedradical]

Sounds like in order for the PESA to have the same amount of capability/performance as the AESA would require a larger radar. I've always made a SWAG that this is the reason why modern Russian Flankers require such a physically large radar.

Yes and that's only to have equal detection range using 1990's technology and AESA technology has improved tremendously since then. PESA radars today are better than they were 20-30 years ago but that's nothing compared to how much AESA technology has improved. Of course AESA tech had other significant advantages over PESA technology even then. They had much better LPI capabilities through much wider bandwidth, higher duty cycle, better power management, better frequency agility and capability to use several simultaneous beams. They also had multi-role capabilities like use as ESM/EW antenna or data link antenna. So it offered better RF stealth and non-radar capabilities. Nowadays the difference in these areas is even bigger with latest technology.

I think you are correct about Russian Flankers. N011M Bars radar in Su-30 weighs something like 650 kg (1431 lbs) whereas AN/APG-77 weighs 524 lbs (or 238 kg)... That's ridiculous difference. Irbis-E is lighter than Bars but still very heavy in comparison to APG-77. Of course PESA radar using Western/US technology would've likely been significantly smaller/lighter but still far more than using AESA technology. According to French Wikipedia and other French sources I could find, RBE2 PESA in earlier Rafales weighs about 270 kg... So even it is heavier than AN/APG-77. Of course there might be some differences in calculating weighs but I think it's safe to say that AN/APG-77 is very light radar. Of course not having traditional back-end also helps it compared to more traditional configurations.

To circle back on this, I don't know if this is an apples to apples comparison, because the AN/APG-77 doesn't have a dedicated backend, but uses the F-22's CIP that also handles other sensors, because the F-22's avionics are so integrated. So I don't know what that weight includes, which is why I don't think it's useful to compare them, because it's not a radar you can just drop in another aircraft.

What's interesting is that the paper discusses the benefits of a tile rather than the brick/notch T/R modules on the AN/APG-77 because it's thinner which potentially allows the array to be conformal instead of being in just a flat array. Even though from a pure performance perspective, the notched T/R modules are better.

From this 2001 USAF acquisition document, the expected power of T/R modules of APG-77, APG-79, and APG-80 era are 2 watts average power and 10 watts peak power.
https://web.archive.org/web/20120920222 ... 391893.pdf

[zero-one]

So there is no dedicated LPI modes as often claimed, but the radar is LPI design in every way.

Question about LPI in general. How is it performed exactly. I've read all kinds of ways
i.e. focusing the waves into a narrow beam to avoid side lobe detection
rapid changes in frequencies to make it harder to track,
lowering power output in a certain way.

There are hints that these LPI modes will limit or reduce the radar's capability, like they won't be able to produce a targeting track when in this mode, or the number of targets that can be tracked is reduced, range is reduced, etc.

Are any of these true?

[sprstdlyscottsmn]

To put it simply, it is advanced signals processing. It has been a constant evolution since at least the F-106. It is the ability to generate a signal that is sufficiently complex that the enemy ESM systems do not recognize it as a radar pulse. Because the system generated it, it can process the returns.

AESA has reduced sidelobes, which helps.
Rapid Frequency changes go back to the F-106.
Lowering power output applies once a track has been established so that even as range gets closer the enemy actually receives less energy for its ESM systems as the transmitter radar only needs to receive the same amount of energy.

[hornetfinn]

So there is no dedicated LPI modes as often claimed, but the radar is LPI design in every way.

Question about LPI in general. How is it performed exactly. I've read all kinds of ways
i.e. focusing the waves into a narrow beam to avoid side lobe detection
rapid changes in frequencies to make it harder to track,
lowering power output in a certain way.

There are hints that these LPI modes will limit or reduce the radar's capability, like they won't be able to produce a targeting track when in this mode, or the number of targets that can be tracked is reduced, range is reduced, etc.

Are any of these true?

I think we have gone through this several times, but basically LPI are generally set of features and techniques used and not modes for a radar. These documents describe LPI features and techniques very well:

DETECTION AND JAMMING LOW PROBABILITY OF INTERCEPT (LPI) RADARS:
https://core.ac.uk/download/pdf/36696271.pdf

LPI waveforms for AESA radar:
https://www.diva-portal.org/smash/get/diva2:1443827/FULLTEXT01.pdf

Most of those techniques actually improve range, especially when there is some interference like jamming, chaff or clutter present.

Basically the signal can be very strong if you know what to listen to (like the LPI radar itself does), but would be very much like background noise to everybody else. The signal is spread over wide bandwidth and coded with complex and preferably (pseudo-)random way. There isn't some huge spike in spectrum at all like with older radars.

[Scorpion82]

To circle back on this, I don't know if this is an apples to apples comparison, because the AN/APG-77 doesn't have a dedicated backend, but uses the F-22's CIP that also handles other sensors, because the F-22's avionics are so integrated. So I don't know what that weight includes, which is why I don't think it's useful to compare them, because it's not a radar you can just drop in another aircraft.

If you read the doc posted in the OP you'll see that the radar consists of the array incl. controller, support electronics, receiver and power supply. Only the processing is offloaded to the CIP. So these elements form the radar set.

[spad_s.xiii]

If anyone like to know more about LPI radar, detection and CM, I'd recommend this book, which I think is very good (Detecting and Classifying Low Probability of Intercept Radar, by Philip E. Pace): https://a.co/d/j9lhjQH
You won't immediately become an EW expert after reading it, but you will know more than most aeronautical enthusiasts.