The mystery of the "Bandpass Radome"

[Dalai Lama]

It sounds like the same principle applied in sound engineering. I assume in this case, the radome material is equivalent to the "gates". Basically allowing certain frequencies to pass but attenuating frequencies it's designed to reject. What the material is... I've no idea...

 

[siegecrossbow]

I think it will be simpler than that...as in one way radome which only allows transmission but no reception....

Or filtering by wattage not frequency as that way it will be simpler...Radar signals upto certain watts are absorbed by the coating and scattered by the shape of the dome..Any waves above certain watts will still be scattered and absorbed but part of it will make it to the radar receiver...
The antenna will start with bursts of energy in selected directions and if targets picked .. it will continue to transmit high power concentrated radar waves in that direction instead of scattering waves all over the place.
Either that or a one way radome.....Dont know..just speculating like evrybody else.

Kinda like a oneway mirror except with radar waves instead of visible light?

I've done band-pass filtering of signals in my digital signal processing class. I wonder if the basic principles are similar. As long as the radar frequencies within the cutoff frequencies they can pass through. Enemy radar frequencies, which are presumable outside of the passband, would be filtered out by the material.

^^ Just wild guesses.

 

[Safriz]

Kinda like a oneway mirror except with radar waves instead of visible light?

I've done band-pass filtering of signals in my digital signal processing class. I wonder if the basic principles are similar. As long as the radar frequencies within the cutoff frequencies they can pass through. Enemy radar frequencies, which are presumable outside of the passband, would be filtered out by the material.

^^ Just wild guesses.

Exactly....like the mirror tint of your car's windows...you can look out but people cant look in?

There is only one problem with bandpass...It will make the F-22 radar limited and prone to jamming..as a "Listening" enemy jamming station will know the limited range of transmission by the F-22 radar and jam the spectrum...as it will be limited by the bandpass mechanism....It will only transmit within a certain range of frequency...
Plus the enemy will only have to listen to signals outside their own frequency spectrum and if they receive a radar signal outside their own frequency spectrum they will know for sure that its an F-22
On the other hand if its not bandpass,the spectrum can be much broader and difficult to trace and jam..

Another wild guess

 

[siegecrossbow]

Exactly....like the mirror tint of your car's windows...you can look out but people cant look in?

There is only one problem with bandpass...It will make the F-22 radar limited and prone to jamming..as a "Listening" enemy jamming station will know the limited range of transmission by the F-22 radar and jam the spectrum...as it will be limited by the bandpass mechanism....It will only transmit within a certain range of frequency...
Plus the enemy will only have to listen to signals outside their own frequency spectrum and if they receive a radar signal outside their own frequency spectrum they will know for sure that its an F-22
On the other hand if its not bandpass,the spectrum can be much broader and difficult to trace and jam..

Another wild guess

The F-22 keeps its radar closed for the majority of the mission. AWACs do most of the scouting until it is time for the raptors to go for the kill.

 

[Safriz]

extracts from website

F-22 Stealth

Radar absorbant materials, or RAM is applied sparingly on the F-22 airframe as opposed to the entire airframe on the F-117. This is because designers have incorporated curves on crucial surfaces and edges, which lessens the need for RAM. For example, new ceramic-matrix RAM is utilized on the engine exhaust nozzles to reduce radar and IR signatures, and a greater amount of wide-band structural RAM is used on the wing edges. The interesting shape of the radome on the F-22 reflects radar signals at all frequencies except the precise wavelengths emitted from the F-22. This can be attributed to the radome's low bandpass type.

 

[siegecrossbow]

extracts from website

F-22 Stealth

Radar absorbant materials, or RAM is applied sparingly on the F-22 airframe as opposed to the entire airframe on the F-117. This is because designers have incorporated curves on crucial surfaces and edges, which lessens the need for RAM. For example, new ceramic-matrix RAM is utilized on the engine exhaust nozzles to reduce radar and IR signatures, and a greater amount of wide-band structural RAM is used on the wing edges. The interesting shape of the radome on the F-22 reflects radar signals at all frequencies except the precise wavelengths emitted from the F-22. This can be attributed to the radome's low bandpass type.

THe passage seems to imply that the shaping of the radar dome is responsible for the the bandpass filtering. We can potentially deduce the frequency of F-22's radar if we understand more about how the process actually works.

 

[gambit]

Thanks for the info. It truly is a very exotic science, one little thought about. And I would guess that an F-22 radome (for example) is TOP SECRET in terms of materials and construction.

A very big leap from a fiberglass radome on an F-106!

Something else to consider - radars today are frequency agile, and might hop through many gigahertz, meaning the radome would have to be transparent throughout the range. I'll bet a cookie that these radomes are active in some sense - perhaps they apply a charge through a mesh, turning transparency ON and OFF in time with the radar pulses themselves.

Not quite 'active', but I know we are working on that front. Currently I am in the semicon manufacturing industry, specifically NAND, previously DRAM. The techniques we used to create these nanometer scale transistors and capacitors are being explored to create active absorbers.

If you do keyword search for 'ansoft frequency selective surfaces' where 'ansoft' is a software company, you will open up a pdf layman's guide to FSS. On slides 3 and 5 you will see various shapes of 2D structures that are 'printed' onto a resistive sheet. It is these structures that allow the bandpass/bandstop capability of these sheets. This is public information. However, it is the quality of manufacturing of these sheets, the precision of these structures, and the combinations of layers of these sheets that are felonious secrets. Radar absorbers works the same way. FSS are essentially absorbers but more sophisticated in design, then more complex and costly to manufacture.

In the ANSOFT presentation, slide 20 shows a typical 'woodpile' stacking of several sheets of different dielectric structures as how a combination of sheets can have a bandpass of one frequency but a bandstop of another frequency.

Another factor in these bandpass/bandstop capabilities is angle of incidence, meaning the angle of the impinging radar signals upon the radome, internally and externally. The nose of the F-22 is not shaped that way due to aerodynamics and RCS control measures alone. Believe it but a major factor of that shape is how adversary radar signals can impact the radome, how they behave on its surface, and how we can exploit that behavior to minimize leak through but maximize our transmission strength and our signal fidelity. In other words, we can have a certain sheet with certain 2D structures to influence an external surface wave on the radome while internally another sheet with different 2D structures will allow the maximum of our own seeking radar signals in terms of power and beam fidelity through the radome.

Bottom line is this: ALL radomes are essentially bandpass structures. For today, some are more sophisticated than others and the US has the far lead.

 

[gambit]

Exactly....like the mirror tint of your car's windows...you can look out but people cant look in?

There is only one problem with bandpass...It will make the F-22 radar limited and prone to jamming..as a "Listening" enemy jamming station will know the limited range of transmission by the F-22 radar and jam the spectrum...as it will be limited by the bandpass mechanism....It will only transmit within a certain range of frequency...
Plus the enemy will only have to listen to signals outside their own frequency spectrum and if they receive a radar signal outside their own frequency spectrum they will know for sure that its an F-22
On the other hand if its not bandpass,the spectrum can be much broader and difficult to trace and jam..

No, it does not.

Another wild guess

I do not.

 

[Safriz]

janes website says that the radar on F-22 is an X-band 8 to 12.5 Ghz radar so thats normal frequency range for any X-Band radar.....no seperate frequency spectrum for F-22.
articles.janes.com/articles/Janes-Radar-and-Electronic-Warfare-Systems/AN-APG-77-United-States.html
another website f22raptor.com(dont know if its reliable or not)
says that the radar antenna itself is low radar cross section..its divided in 2000 seperate small tranceivers arranged in three sections..middle facing forwars and two more facing starboard and port.and there are no.moving parts in the antenna.
such an antenna in itself will be stealth as it will scatter enemy radar waves in all different directions instead of reflecting them.
so the radome doesnt need to be too complicated anyway....or does it?
and here is northrop grummens own website describing the APG-77 radar and repeatedly attributing stealthiness to low radar cross section of the aesa antenna..says nothing about radome.
www.es.northropgrumman.com/solutions/f22aesaradar/

oh well different infos on different websites...

 

[Safriz]

just found this news article.
airforcetimes.com/mobile/index.php?storyUrl=http%3A%2F%2Fwww.airforcetimes.com%2Fnews%2F2011%2F03%2Fdefense-f22-raptor-absent-from-libya-ops-032211%2F
it says that the F-22 link 16 is limited to listen only and can transmit to other raptors only and cannot talk to NATO planes...also it says that F-22 is next to useless for ground attacks.
now after reading this article i am convinced that the deshgners may have sacrificed the functionality of radar by limiting bandwidth and drastically complicated the radome only for the sake of perfect stealth..althouth as argued above the radar antenna with many infividual transponders in three plsnes was slready stealtjfue yo bery low RCS...But desighners may have wanted to completely vonce it by incorporating bandpass....i was arguing against bandpass as IMO it will reduce the radars usability.
if i am wrong..i would like to be proved wrong..this is a speculative discussion after all.

 

[Chogy]

Some good information and educated guesses too, thanks Gambit and others.

I guess the thing that amazes me most is that it is true the Raptor doesn't have a monopoly on a frequency band. There is no specific special "Raptor-only" frequency like 12.87495664536 gigahertz. Since the Raptor is frequency agile, the radome needs to work over the same range.

The notion of receptor modules outside the radome is interesting and possible. With AESA technology, there is nothing to prevent the vertical stabs, for example, from being active emitting surfaces. More than one radar on the jet.

 

[OrionHunter]

Any engineers want to explain how this is done?

Are you aware that much of the F-22 is made in those ultra top secret black projects - Lockheed Martin's Skunk Works and Boeing's Phantom Works? Keeping this in mind, do you for a moment think that this top secret technology will be out in the public domain?

There is AI also that helps the pilot fly this toy! And anti gravity propulsion too that can be switched on at the flick of a button! The latter system is incorporated in the B-2 stealth bomber too and is therefore called 'The flying capacitor' that produces a 'gravity well' in front of the craft that allows unlimited range.

With all these super secret technologies aboard, is it any wonder that the F-22 costs a whopping $360 a piece (including R&D) and banned for export?

So, will we ever know how they do it? Not in the near future anyway. Till then, keep guessing!

Cheers!

 

[Safriz]

Are you aware that much of the F-22 is made in those ultra top secret black projects - Lockheed Martin's Skunk Works and Boeing's Phantom Works? Keeping this in mind, do you for a moment think that this top secret technology will be out in the public domain?

There is AI also that helps the pilot fly this toy! And anti gravity propulsion too that can be switched on at the flick of a button! The latter system is incorporated in the B-2 stealth bomber too and is therefore called 'The flying capacitor' that produces a 'gravity well' in front of the craft that allows unlimited range.

With all these super secret technologies aboard, is it any wonder that the F-22 costs a whopping $360 a piece (including R&D) and banned for export?

Cheers!

and F-22 can time warp and fire black holes.
now where should i bang my head.

 

[Safriz]

guess what i found on ebay.
Jet nose cone F-22 Jet fighter | eBay

 

[manojb]

guess what i found on ebay.
cgi.ebay.com/Jet-nose-cone-F-22-Jet-fighter-/220702006672

Good! some country can order that part and start building stealth plane based on that. work from nose end to rear end!!