Stealth vs ECM

[Charge]

You got something mixed there Boz.

"Emissions from your plane announce your presence, but measuring your exact location and speed for the purpose of guided armament is not easy. Normally it takes triangulation from several displaced receivers to do it and it is still not very fast or accurate."

You emitting radar radiation is no different from a system that lights you with radiation (except that your emission has more power) and a missile homing on you e.g. beam-rider missiles. Also SHRIKE and HARM were meant to do just that, home on radar emission. I guess the new AARGM is still more powerful in homing. The problem with employing this kind of missiles is always the same: what if the enemy shuts down his radar? Homing on a ground based cold radar is easy using INS/GPS if you get the initial reading but in the air it is impossible, but the fact remains, if you have your radar on you can be tracked and the accuracy depends on the antenna system on the receiving end.

"If you want to hide your presence, the plane has to fly in complete electronic silence. This means no radio, no radar, no active ECM, no data-links."

You could also rank them while your at it.

1. Radar (Hey here I am!) (Power is in kilowatts)
2. ECM (Hey, I'm somewhere in this direction!) (Power is in kilowatts)
3. Datalink (https://www.rockwellcollins.com/sitecore/content/Data/Products/Communications_and_Networks/Data_Links/Joint_Tactical_Information_Distribution_System.aspx) (MIDS has the same power rating, 200W)
4. Radio (Hey, Im around!) (Power is probably a couple of hundred watts)

Datalink and radio are probably not much different except that with radio you can choose when to reply (and emit power). Datalink is mainly on one direction but I suppose the system sends some data back to announce it has received data. Thus the radiation is not entirely dependent of the pilot in the fighter. But the operating mode of radio and datalink makes them very hard to track. If you know the frequencies you can tell that something is going on but where and what is more difficult to figure out.

-C+

[bozon]

You got something mixed there Boz.

"Emissions from your plane announce your presence, but measuring your exact location and speed for the purpose of guided armament is not easy. Normally it takes triangulation from several displaced receivers to do it and it is still not very fast or accurate."

You emitting radar radiation is no different from a system that lights you with radiation (except that your emission has more power) and a missile homing on you e.g. beam-rider missiles. Also SHRIKE and HARM were meant to do just that, home on radar emission. I guess the new AARGM is still more powerful in homing. The problem with employing this kind of missiles is always the same: what if the enemy shuts down his radar? Homing on a ground based cold radar is easy using INS/GPS if you get the initial reading but in the air it is impossible, but the fact remains, if you have your radar on you can be tracked and the accuracy depends on the antenna system on the receiving end.

I was refering to all emissions in general. However, even the radar does not give your location with sufficient accuracy to guide weapons to you. Anti radar missiles such as HARM have a low angular resolution - they just get close enough to the target till the low resolution is sufficient... They also repeatedly measure and correct the calculated location of the target as they fly, thus require a certain flight path to acquire the target with sufficient accuracy to follow and get close enough. Also, remember that ground radars are always at altitude zero AGL. If you know the direction in 3D space and know where the ground is, you know the range. No so in the air.

This will not do to intercept a flying target. To track your position as if you are tracked by a radar they need multiple antennas that read the direction to you and then triangulate. This is quite clumsy and used as intel but not to actively track you. The radar on the plane can jump frequencies and is not so easy to get a good triangulation on with a high update rate. So yes, they know you are there, they know roughly where you are, but then they still have to acquire you by other means attached to a weapon system in order to do anything about it.

[GScholz]

First of all it isn't correct...

The radar still needs to form a beam - which is done by multiple sources working on the same frequencies on different phases - it is the plane physics (see interference).

That's the older PESA radars with the single microwave source and a series of delays to drive the array. In the AESA, each element is driven at a different frequency, even within a single pulse, so there is no high-power signal at any given frequency. The radar unit knows which frequencies were broadcast, and amplifies and combines only those return signals, thereby reconstructing a single powerful echo on reception. The target is unaware of which frequencies are active and has no strong signal making detection on radar warning receivers very difficult.

[Charge]

I stumbled upon a seeker type 9B-1032 which suggests that Russia may have a passive radar homing A to A seeker.

-C+

[artik]

That's the older PESA radars with the single microwave source and a series of delays to drive the array. In the AESA, each element is driven at a different frequency, even within a single pulse, so there is no high-power signal at any given frequency.

It has nothing to do with PESA it has to do with physics and waves.

For example lets have to coherent sources of radio waves of the wavelength 5 cm.

If I turn only one of them than the signal would be distributed equally at 360 degrees. Now I put 2 such sources at the distance of 2.5cm radiating coherently. Now at the direction perpendicular to these two sources the waves would combine and you have a signal twice its strength and in a direction parallel to these sources the signal of one source would be nullified by another because they would be at inverse phase (due to 1/2 wave length distance)

So basically in front of them you get signal twice stronger and at 90% on sides of this simple antenna you get none of the signal and at 45 degrees you have something between them.

More sources you combine the more significant effect becomes - i.e. you create a narrower beam - that goes in specific direction such that you can have a resolution of few degrees and use it to detect the targets.

If each element operates on its own different frequency - you can't create a beam - the different frequencies do not interfere - basically instead of creating a strong concentrated flashlight that radiates in specific direction you get a lamp that illuminates at 360 degrees.

It is just a basic physics of wave propagation.

AESA is not that much different from PESA - the difference is that you can create several directed beams using different frequencies using the same radar instead of using single transmitter and adding delays in the signal...

[GScholz]

I don't make the darn things, I just listen to the people who do. Most of what they say goes over my head, but as far as I've understood it they use advanced digital beamforming to produce agile synthetic wideband waveforms (and ultra low sidelobes). I.e. a waveform that combines many different frequencies that through harmony or disharmony forms the beam. This allows each element or small groups of elements to operate at different frequencies thus spreading the transmitted energy across a wide band of frequencies. Add pseudo-random noise algorithms to the chirp and you get something that is just noise to any RWR that doesn't know exactly what to look for. At least that's how I understand it.

[cegull]

Seems like the Dehaviland mosquito was an early stealth fighter/bomber being made out wood.  It's cover has always been that Britain was running out of strategic metals for building planes and therefore had to use wood, however it had a smaller radar signature for its size.  It was one of the few planes that could be sent into enemy territory by itself.   

[bozon]

Seems like the Dehaviland mosquito was an early stealth fighter/bomber being made out wood.  It's cover has always been that Britain was running out of strategic metals for building planes and therefore had to use wood, however it had a smaller radar signature for its size.  It was one of the few planes that could be sent into enemy territory by itself.    

That is a myth. The mossie shows just fine on radar. "All wood" refers to the fuselage and wings. The engines, cables, landing gears, electronics, and like a million nails had plenty of metal in them.

Birds show on radar btw, even those without lead pellets in their body.

[Puma44]

That is a myth. The mossie shows just fine on radar. "All wood" refers to the fuselage and wings. The engines, cables, landing gears, electronics, and like a million nails had plenty of metal in them.

Birds show on radar btw, even those without lead pellets in their body.

Not to mention the props.  Huge radar reflectors.

[Zimme83]

That is a myth. The mossie shows just fine on radar. "All wood" refers to the fuselage and wings. The engines, cables, landing gears, electronics, and like a million nails had plenty of metal in them.

Birds show on radar btw, even those without lead pellets in their body.

The first German radars had a wavelength measured in meters so even the engines of the moss where too small to reflect the radar signal and it was therefore invicible on radar. However the german switched to smaller wavelengths that could detect the Moss pretty soon.

But there are other examples of ww2 stealth aircrafts: http://en.wikipedia.org/wiki/Horten_Ho_229#Stealth_technology

"RCS testing showed that a hypothetical Ho 229 approaching the English coast from France flying at 885 kilometres per hour (550 mph) at 15–30 metres (49–98 ft) above the water would have been visible at a distance of 80% that of a Bf 109. This implies a frontal RCS of only 40% that of a Bf 109 at the Chain Home frequencies. The most visible parts of the aircraft were the jet inlets and the cockpit, but caused no return through smaller dimensions than the CH wavelength. Given the high-speed capabilities of the aircraft it would have given the British defences just two and a half minutes to respond, which would not have been enough time. It is believed that, if deployed in quantity, the Ho 229 could have changed the course of the war"

Btw almost all modern fighters (in the west atleast) has a lot of stealth features, like the design of the air intake etc. Planes like Gripen, EF and Rafale are not as extreme as the F-22 but their rcs is much smaller than the rcs of their predecessors.