Band pass radome use on fighters

Vanessa1402

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Apart from pure stealth fighters such as F-22, F-35, Su-57, J-20 Do normal fighters such as Eurofighter, F-18 E/F and Rafale have band pass radome?
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Ronny

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Trident

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Do you have a source which states unequivocally that the Rafale doesn't? There was a Jane's IDR article a while ago where Dassault stated they did not plan to take full advantage of the wide bandwidth capabilities of AESA in RBE2-AA because doing so would require a radome redesign. The point of comparison was specifically the more-than-a-radar approach on the Super Hornet (which, as Ronny states, has a separate removable screen). The radome limiting radar bandwidth is kind of a big clue that it is a FSS design, I'd think.
 

overscan (PaulMM)

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It wouldn't be surprising if the radome on Rafale was FSS. Both Rafale and Typhoon tried to minimise the major RCS contributors, though neither is "stealthy".
 

icyplanetnhc (Steve)

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FSS radomes should be standard on stealth fighters. Even so, they have their radar antennas tilted away from the frontal axis in the event that hostile frequencies happen to be at the correct bands.
 

sferrin

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I wonder if the B-1B has one. They made quite an effort to reduce RCS.
 

Vanessa1402

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Do you have a source which states unequivocally that the Rafale doesn't? There was a Jane's IDR article a while ago where Dassault stated they did not plan to take full advantage of the wide bandwidth capabilities of AESA in RBE2-AA because doing so would require a radome redesign. The point of comparison was specifically the more-than-a-radar approach on the Super Hornet (which, as Ronny states, has a separate removable screen). The radome limiting radar bandwidth is kind of a big clue that it is a FSS design, I'd think.
I haven't read that article, can you link it here?
btw,I can't find any source that state directly Rafale doesn't have FSS radome. But I can't find any source that state it has a FSS radome either. In fact, Dassault brochure only seem to list Saw tooth, S-duct, RAM as RCS reduction feature on Rafale. I looked up the radome manufacturer of Rafale, but they didn't mention anything about FSS or bandpass radome either, so I conclude that Rafale doesn't use FSS
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Vanessa1402

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It wouldn't be surprising if the radome on Rafale was FSS. Both Rafale and Typhoon tried to minimise the major RCS contributors, though neither is "stealthy".
While it would make a lot more sense for Rafale to have FSS, evidences seem to suggest otherwise. Also afaik, F-16 doesn't have FSS radome, eventhough, it undergo RCS reduction with Have glass, Have glass II and Have glass V (I could be wrong on this but it seem like the inlet of F-16 is not coated with Have glass RAM either, I don't know why)
 

overscan (PaulMM)

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Perhaps Rafale's RBE2 was less conspicuous on radar than the mechanically scanning CAPTOR. It will reflect strongly only dead ahead while CAPTOR could be a reflector at any angle in the front hemisphere.
 

Trident

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I haven't read that article, can you link it here?


Page 11. Perhaps knowing the French technical term for FSS or bandpass would help the Google hit rate. Unfortunately, having learned it at school, (what remains of) my French vocabulary is the polar opposite of my Russian (which consists practically entirely of technical terms)...

In fact, Dassault brochure only seem to list Saw tooth, S-duct, RAM as RCS reduction feature on Rafale.

It doesn't explicitly mention the conducive canopy coating either, yet it's clearly present. Being a Dassault presentation, it may only refer to those RCS reduction measures under Dassault's direct control, not those supplied in finished form by others.

While it would make a lot more sense for Rafale to have FSS, evidences seem to suggest otherwise.

Classic case of absence of evidence not equating to evidence of absence, methinks.
 
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Trident

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Perhaps Rafale's RBE2 was less conspicuous on radar than the mechanically scanning CAPTOR. It will reflect strongly only dead ahead while CAPTOR could be a reflector at any angle in the front hemisphere.

I'd argue it's the other way round actually - aircraft with LO ambitions which do not have FSS radomes tend to use canted radar faces if the system has a fixed phased array. Super Hornet and B-1B come to mind.
 

mkellytx

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I wonder if the B-1B has one. They made quite an effort to reduce RCS.
IIRC the Bone primarily got theirs from the angle of the antennae and that it was a PESA. Can't seem to recall anything about bandpass radomes on the attack radar.
 

Vanessa1402

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Perhaps Rafale's RBE2 was less conspicuous on radar than the mechanically scanning CAPTOR. It will reflect strongly only dead ahead while CAPTOR could be a reflector at any angle in the front hemisphere.

I'd argue it's the other way round actually - aircraft with LO ambitions which do not have FSS radomes tend to use canted radar faces if the system has a fixed phased array. Super Hornet and B-1B come to mind.
VLO fighters seem to apply both method, FSS radome and tilting their radar
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Vanessa1402

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I haven't read that article, can you link it here?


Page 11. Perhaps knowing the French technical term for FSS or bandpass would help the Google hit rate. Unfortunately, having learned it at school, (what remains of) my French vocabulary is the polar opposite of my Russian (which consists practically entirely of technical terms)...

In fact, Dassault brochure only seem to list Saw tooth, S-duct, RAM as RCS reduction feature on Rafale.

It doesn't explicitly mention the conducive canopy coating either, yet it's clearly present. Being a Dassault presentation, it may only refer to those RCS reduction measures under Dassault's direct control, not those supplied in finished form by others.

I tried searching for the term in French but couldn't find anything. The radome manufacturer of Rafale radome also only claim that their radome is very transparent
 

Trident

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VLO fighters seem to apply both method, FSS radome and tilting their radar

Yes, once you go beyond Eurocanard/SH levels of RCS reduction you apparently have to use every trick in the book and it is no longer an either/or option.
 

Vanessa1402

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@ALL on a side note, does anyone know the resting position of missile radar seeker before they are launched?. Do they point forward or slightly tilted?. In other words, when missiles are still on the rail, do their seeker point like this:
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Or like this:
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overscan (PaulMM)

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All conventional radomes are narrowband. They are designed to work correctly with best transmission characteristics at a given wavelength e.g. 9GHz matching the radar. You can't change the radar frequency too far from this without designing a new radome. This isn't the same as FSS (frequency selective) radomes, which actively block frequencies outside of a desired range.

A wideband radome can be used across a wide range of frequencies like 1 - 18 GHz or something. LPI AESA radars use spread-spectrum techniques and so tend to work across a much wider range of frequencies.
 

Ronny

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All conventional radomes are narrowband. They are designed to work correctly with best transmission characteristics at a given wavelength e.g. 9GHz matching the radar. You can't change the radar frequency too far from this without designing a new radome. This isn't the same as FSS (frequency selective) radomes, which actively block frequencies outside of a desired range.

A wideband radome can be used across a wide range of frequencies like 1 - 18 GHz or something. LPI AESA radars use spread-spectrum techniques and so tend to work across a much wider range of frequencies.
Isn't normal radome made from material which are transparent to radiowave like kelva or fiber glass (aka non conductor) ? Why would it has narrow band limit?
 

overscan (PaulMM)

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Isn't normal radome made from material which are transparent to radiowave like kelva or fiber glass (aka non conductor) ? Why would it has narrow band limit?

It really isn't that simple. Yes, they are made from essentially radar transparent materials, but they are still designed to have best characteristics at a design frequency / wavelength and radar signals outside that might get bent, partially reflected, attenuated etc.


TYPES / CLASSES / STYLES

Radomes for use on flight vehicles, surface vehicles and fixed ground installations are classified into various categories according to MIL-R-7705B. Categories are determined by the specific radome use and wall construction. Customer satisfaction is met by the following,

Type’s definitions

Type I:
low frequency radomes at or below 2 GHz.
Type II: Directional guidance radomes having specified directional accuracy and requirements. Bore sight error (BSE), bore sight error slope (BSES), antenna pattern distortion and antenna side lobe degradation.
Type III: narrowband radomes with an operational bandwidth less than 10%.
Type IV: multiple frequency band radomes used at two or more narrow frequency band.
Type V: broadband radomes generally providing an operational bandwidth between 0.100GHz and 0.667GHz
Type VI: very broadband radomes that provide and operational bandwidth greater than 0.667GHz.

Style definitions

Radome styles are defined according to the dielectric wall construction. There are 5 basic styles.
Style A: Half wave wall solid (monolithic).
Style B: Thin wall monolithic with a wall thickness equal to or less than 0.1 wavelengths at the highest operating frequency.
Style C:
A-Sandwich multi-layered wall. Consisting of three layers two high density skins and a low density core. The dielectric constant of the skins is greater than the dielectric constant of the core material. 0.25 wavelengths.
Style D: Multi layered wall having 5 or more dielectric layers. Odd number of high density layers and an even number of low density core layers. As the number of layers is increased, the broadband frequency performance is improved.
Style E: Other radome wall constructions not fitting into the above style definitions. Including the B-Sandwich consisting of two low density skins and a high density core. Dielectric constant of the skins is less than the dielectric constant of the core.

RADOME CHARACTERISTICS

It has been well-known for some time that the presence of a radome can affect gain, beam width, side lobe level, and the direction of the bore sight, or pointing direction of a radar antenna. The radome characteristics are classified in to Electrical Characteristics , Mechanical Characteristics

Electrical Characteristics

The electrical-performance characteristics are quantified in terms of transmission loss, beam deflection, pattern distortion and reflected power.

A. Transmission Loss
The transmission loss is a measure of energy loss due to reflection and absorption as a result of transmission of the signal through the radome. Faulty repair procedures can create regions of transmission loss not present in the original radome.

B. Beam Deflection
Beam deflection, also known as bore sight error, is the shift of the main-lobe electrical axis due to the presence of the radome.

C. Pattern Distortion
Pattern distortion due to the presence of an incorrectly repaired radome can cause changes in the mainlobe beam widths, null depths and the structure of the side lobes.

D. Reflected Power
Reflected power can cause degradation of the pattern and raise side lobe levels. It can also cause frequency pulling of a magnetron.
 
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Vanessa1402

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I haven't read that article, can you link it here?


Page 11. Perhaps knowing the French technical term for FSS or bandpass would help the Google hit rate. Unfortunately, having learned it at school, (what remains of) my French vocabulary is the polar opposite of my Russian (which consists practically entirely of technical terms)...

From Overscan and Ronny discussion above, we can safely conclude that Rafale doesn't have Bandpass radome. It has a narrow band radome like F-16
 

Ronny

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I haven't read that article, can you link it here?


Page 11. Perhaps knowing the French technical term for FSS or bandpass would help the Google hit rate. Unfortunately, having learned it at school, (what remains of) my French vocabulary is the polar opposite of my Russian (which consists practically entirely of technical terms)...

From Overscan and Ronny discussion above, we can safely conclude that Rafale doesn't have Bandpass radome. It has a narrow band radome like F-16
The grid mesh used by Dassault aviation to compute the radiated pattern of the conformal antenna on Rafale also suggest that the radome is non conductive, so it must be transparent to RF wave.

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quellish

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Just because it is not conductive does not mean it is transparent to RF.
In this particular case it probably is, but it is not safe to assume a non conductive or dielectric material is RF transparent or does not alter the RF signal. Some dielectric materials will pass through a signal from one direction but reflect it from another, and absorb from another!
 

Ronny

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Just because it is not conductive does not mean it is transparent to RF.
In this particular case it probably is, but it is not safe to assume a non conductive or dielectric material is RF transparent or does not alter the RF signal. Some dielectric materials will pass through a signal from one direction but reflect it from another, and absorb from another!
If I recall correctly, the reflection of radiowave is due to the induced current generated when the wave hit a surface, so I don't see how a non conductor can reflect radio wave
 

Trident

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Non-reflective =/= transparent. And properties can be anisotropic, as mentioned.
 

Ronny

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And also radar wave must travel both way, in and out the radome, otherwise the radar doesn't work

properties can be anisotropic, as mentioned.
Yes some properties can be anisotropic, but a radar is not the same as a jammer. If you make radome absorb radar wave in one direction , it still affect the radar performance. So within the frequency that radar operate ,the radome can't interfere with the wave.
 
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steelpillow

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Just because it is not conductive does not mean it is transparent to RF.
In this particular case it probably is, but it is not safe to assume a non conductive or dielectric material is RF transparent or does not alter the RF signal. Some dielectric materials will pass through a signal from one direction but reflect it from another, and absorb from another!
If I recall correctly, the reflection of radiowave is due to the induced current generated when the wave hit a surface, so I don't see how a non conductor can reflect radio wave
What matters is the characteristic impedance of the surface. Any mismatch from the approx. 377 ohms impedance of free space (Z0) will result in a reflected wave; the greater the mismatch, the greater the amount reflected (I used to design reflectometers for measuring exactly this). Conductive surfaces have very low impedance and are therefore good at reflecting. Equally, some insulators with particular magnetic properties can have very high impedances and therefore, perhaps counter-intuitively, also return a significant reflection. The aim of a stealthy material is to match Z0 as closely as possible.
 
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