Radar questions

[wuzak]

My (limited) understanding of today's fighter radars is that they operate on the X-band frequency. Thus the stealth designs have evolved to combat that frequency band.

But can radars receive and process signals from outside their nominal frequency range? Can they receive L-band transmissions, for instance?

 

[meatloaf109]

Any system is restricted to the things that they are designed to do. So if the system is supposed to opperate on a certain frequency, that is where it is.
A.M. radio will not pick up F.M. and vice versa.
I was an electronics tech in a past life, and if you would like a more detailed explanation, P.M. me.

 

[Matt308]

Supposedly, first generation stealth (e.g., SR-71/F-117) is countered with a networked radar system wherein an emitter RF is received by multiple known location receivers (must be very precise measurements and dynamically updated). Processors then compute time reflections to triangulate location stealth airframe. More modern stealth is based upon not just reflection but absorption.

 

[wuzak]

Any system is restricted to the things that they are designed to do. So if the system is supposed to opperate on a certain frequency, that is where it is.
A.M. radio will not pick up F.M. and vice versa.
I was an electronics tech in a past life, and if you would like a more detailed explanation, P.M. me.

Ok, so an X-band radar set will only receive X-band radar signals, no matter the source? Similarly for other bands.

 

[wuzak]

Supposedly, first generation stealth (e.g., SR-71/F-117) is countered with a networked radar system wherein an emitter RF is received by multiple known location receivers (must be very precise measurements and dynamically updated). Processors then compute time reflections to triangulate location stealth airframe. More modern stealth is based upon not just reflection but absorption.

But reflection is still the biggest part?

 

[meatloaf109]

Not on the stealth systems as I understand them, they work on the idea that they "deflect" radar rather than "absorbing" or reflecting. If you can cause a duck to look like a mosquitoe, well, there it is.

 

[wuzak]

Not on the stealth systems as I understand them, they work on the idea that they "deflect" radar rather than "absorbing" or reflecting. If you can cause a duck to look like a mosquitoe, well, there it is.

That was the idea with the F-117 - deflect the radar signal rather than reflect it directly back. Much the same as now. Of course deflection is reflection off an oblique surface.

 

[wuzak]

Is Radar absorbing material wavelength dependent? That is, is RAM optimised for certain radar bands, or does it work for all?

 

[Matt308]

DC to light.

Just kidding. Optimized for certain bands.

 

[dobbie]

The 2nd generation includes what is known as "iron ball paint". It absorbs the radar frequencies which its tuned to and turns it into heat which is then absorbed by the airframe. As I understand it, its literally small metal balls mixed in with the paint, maybe something along the lines of metallic paint.

 

[wuzak]

Thanks guys.

 

[Wavelength]

If you can cause a duck to look like a mosquitoe, well, there it is.

That's the key to understanding it. If the return can be minimized enough, then signal to noise ratio required for detection and acquiring can not be attained except at extremely short range. This was the concept behind the Horten bomber of WWII. The existing Allied air warning radars could detect it, but but only from a very short range. At 400+ knots it was too late to do anything about it.

Stealth for ships didn't work so great. In tests the radar operator simply turned off his sea clutter filter and where there was a black hole in the sea clutter, there was the stealth ship.

 

[Gixxerman]

This was the concept behind the Horten bomber of WWII. The existing Allied air warning radars could detect it, but but only from a very short range. At 400+ knots it was too late to do anything about it.

This is more related to the WW2 section but I have to chip in here.
There are a lot of claims made about the stealth aspect of the Horten 9/229 and I think most of them don't really stand up to examination.

When Northrop The History Channel tested it on the radar pole against what would have been a contemporary British radar it gave 80% of the signal an Me (BF) 109 would have.
Given the Me (BF) 109 is about as un-stealthy a plane as possible I'd say a 20% reduction trying to cross a coastline bristling (thanks to the V1 campaign) with radar directed proximity fused AAA doesn't amount to a whole lot is not exactly a whole lot of use, even at 400mph or so.

It's also worth bearing in mind that the model that was tested was perfectly built, hardly the true standard of 1945 German manufacture.

Back OT

Wasn't very long wave radar (metric, WW2 German style? ) thought or claimed to be suitable at detecting the F117 type stealth?
I'm sure I read about the B2 visiting the UK for a show on one occasion being tracked by one of the British radars (although undoubtedly all the data was given over to help fill this - if true - 'blind-spot')?

 

[davparlr]

This is more related to the WW2 section but I have to chip in here.
There are a lot of claims made about the stealth aspect of the Horten 9/229 and I think most of them don't really stand up to examination.

When Northrop The History Channel tested it on the radar pole against what would have been a contemporary British radar it gave 80% of the signal an Me (BF) 109 would have.
Given the Me (BF) 109 is about as un-stealthy a plane as possible I'd say a 20% reduction trying to cross a coastline bristling (thanks to the V1 campaign) with radar directed proximity fused AAA doesn't amount to a whole lot is not exactly a whole lot of use, even at 400mph or so.

It's also worth bearing in mind that the model that was tested was perfectly built, hardly the true standard of 1945 German manufacture.

Any aircraft that has a direct view of jet engines are not going to be stealthy in that direction. The Horten design has engines placed very clearly in view to the front and rear, the most important directions. These are excellent radar reflectors.

Wasn't very long wave radar (metric, WW2 German style? ) thought or claimed to be suitable at detecting the F117 type stealth?
I'm sure I read about the B2 visiting the UK for a show on one occasion being tracked by one of the British radars (although undoubtedly all the data was given over to help fill this - if true - 'blind-spot')?

Long wave radar may be able to detect the presence of a stealth aircraft but the resolution is poor and directing a precision weapons system, whether aircraft or missile, to intercept range is problematic. While flying in commercial airspace, in a non wartime situation, the B-2 would never be configured for stealth operation, in fact, it is required to be able to be tracked.

 

[davparlr]

Stealth aircraft are designed to mitigate all types of known or projected sensors, including Rf (radar), IR (heat), audio (sound), EMI (electromagnetic interference radiation), and visual detection (primarily night missions for bombers).

 

[wuzak]

Long wave radar may be able to detect the presence of a stealth aircraft but the resolution is poor and directing a precision weapons system, whether aircraft or missile, to intercept range is problematic.

In the case of a missile surely it could be positioned withion its own seeker's range? Particularly IR missiles.

Also, wouldn't it aid the main attack radar in narrowing the search area?

 

[davparlr]

In the case of a missile surely it could be positioned withion its own seeker's range? Particularly IR missiles. Also, wouldn't it aid the main attack radar in narrowing the search area?

Missile Rf sensor (radar) are required to be quite small and therefore severely limited. If a missile is required to be within, say, 5 miles before lock-on of a non-stealthy platform, this range will be much less for a stealth aircraft, probably less than a mile. Again, stealth aircraft, particularly bombers, also address IR and typically have imbedded engines that are not directly visible by a sensor and are also more difficult to detect by missile borne sensors. Fighters have a larger problem. From the front they can be quite effective in signature suppression however, it is very difficult to suppress an afterburner plum in IR.

I don't know much about long wave radar but while I was working on the B-2 I was never aware of a concern for long wave radar and the engineers were aware of its capability. Those engineers were the best in the world in assaying present and future threats and designing countermeasures. I was a controls and displays worker, although I was involved in B-2 improvement programs, and never had a need to know in stealth technology so I never knew. So all my comments are conjecture.

Also, low signature magnifies the effectiveness of countermeasure such as electronic, expendables, decoys, etc. (I also knew nothing about that on the B-2) and makes that job much easier.

The only effective method of detecting an extremely stealthy that I know of is a highly complex netted radar/sensor system that is designed to detect deflected radar signals. This system would be very complex and expensive to implement.

Stealth and/or UCAVs will be a requirement in future battlefields