The F-22 and L-Band Radar

How vulnerable is the F-22 or any VLO aircraft to RCS degredation due to L-Band radar usage?

How effective is an L-Band radar in the leading edge of an aircraft (a la T-50)? Ground based L-Band?

Generally L-Band radars and other low frequency radars are not accurate enough to provide targeting or guidance to weapons. You still need a higher frequency radar for that.

That being said the proposed leading edge L-Band antennas have several problems:
1. They can only determine range and bearing, not height.
2. They can be detected long before detecting a F-22 (the same goes for any radar)
3. The next generation of AAMs are being designed with HARM functions to attack these types of targets (in the air and on the ground) long before the F-22 (or F-35) is detected.

Like Spudman said, the lower the frequency, the lower the angular resolution for a given antenna size. That's why all the low frequency early warning radars have those massive fence-like antennas in order to get reasonable accuracy. Conversely, thats why missile radars like the AMRAAM's operate at a very high frequency in order to fit the antenna in the missile.

Relatively small and conventionally configured airplanes like the F-22 have difficulty dealing with lower frequency radars because the wavelength of the radar's signal is pretty big relative to the size of the features of the airplane. There's no way around this unless you want to make a big airplane with long edges and no small features (like the B-2). Both the F-22 and the F-35 were designed to defeat the higher frequency radars found in fighters and missile seekers, rather than low frequency early warning radar.

As for the leading edge L-band radar in the PAK-FA, I highly doubt they will be very useful given their very small aperture size. You need a really big antenna to do low frequency stuff accurately, and from the standard radar equations and the released information on the PAK-FA, I don't think those radars will do anything ground breaking. What they will do is let every F-22 and F-35 that is listening know that there is a T-50 out there. The Russian's aren't stupid, and I'm sure they put them there for a reason, but I wouldn't believe what the internet is saying about how they render stealth useless...

Ground based L-band can get around the antenna size pretty easily, but they still lack the resolution to give a good weapons quality track on something. The best you will get is that you know something is out there and a general direction, but that's it. You still need to send some airplanes out there (with higher frequency radars) to do your killing, and those are what the F-22 and F-35 are stealthy against.

What do you think the Russians are putting the L-band radars in the wings for? Is it for marketing? Or could the radar provide a very rough location of a stealth aircraft so that the PAK-FA could know where to look?

Well, the SU-35's L-Band stuff was just a proposal from the MFG, IIRC.

Otherwise, something is better than nothing I suppose. It might just be misdirection too.

You guys are forgetting networking. One L-band source won't provide fantastic accuracy but what about multiple units networked together. Widely separated units will reduce the volume that a blip can be in dramatically. Cuing multiple x-band radars to a specific volume will increase the probability of detection and at the very least, even if only working individually, they can cue other platform sensors like IRST.

The standard response to that is they have to give away their position to do that. The real question is, if they can detect or localize all the stealthy birds in the process, does it matter.

jeffb wrote:You guys are forgetting networking. One L-band source won't provide fantastic accuracy but what about multiple units networked together. Widely separated units will reduce the volume that a blip can be in dramatically. Cuing multiple x-band radars to a specific volume will increase the probability of detection and at the very least, even if only working individually, they can cue other platform sensors like IRST.

The standard response to that is they have to give away their position to do that. The real question is, if they can detect or localize all the stealthy birds in the process, does it matter.

I'd think it wouldn't matter, since the systems would be taken down systematically on the first day of the war anyway. Being able to see your enemy without giving yourself away is better than lighting up a flashlight and having everyone know exactly where you are.

I was speaking to the L-band fitted interceptors in my post but I think the thing is, if any fixed installation doesn't have 20/20 vision (vs stealth/ucav/cruise) then it's vulnerable and one or another of those platforms will find away inside its defences and kill it. The advances(?) in point defence are aimed at stopping the leakers but of course they all come with their own limitations.

In the air though I think it doesn't really matter. Sure you may light yourself up like a christmas tree but if it lights up all the stealth birds out there at the same time then does that matter so much?

Jeffb-
I see where you are going, but you probably still can't target the stealth birds. If you get a location and firm direction (not to mention a firm count on number of stealth birds) you are still stuck waiting for your high band radar to get a weapons track. Meanwhile the stealth birds know you are there and that you are trying to track them. Basically you are now playing chicken; you know the stealth(s) are there and they know you are there.

The only problem is that most likely the stealth birds will get a weapons track on you before you get one on them. Then you have to maneuver to avoid the incoming threat(s), thus possibly loosing your L-band track, and now the stealth birds have the upper hand.

Also history indicates that it is likely there will be more F-22/F-35's than L-band equipped SU-35's and T-50's.

Sufa Viper

sufaviper wrote:Jeffb-
I see where you are going, but you probably still can't target the stealth birds. If you get a location and firm direction (not to mention a firm count on number of stealth birds) you are still stuck waiting for your high band radar to get a weapons track. Meanwhile the stealth birds know you are there and that you are trying to track them. Basically you are now playing chicken; you know the stealth(s) are there and they know you are there.

The only problem is that most likely the stealth birds will get a weapons track on you before you get one on them. Then you have to maneuver to avoid the incoming threat(s), thus possibly loosing your L-band track, and now the stealth birds have the upper hand.

Also history indicates that it is likely there will be more F-22/F-35's than L-band equipped SU-35's and T-50's.

Sufa Viper

I don't know Sufa, three or four firm directions will put a pretty small box around a target, even a vlo one assuming that L-band see them at all. I don't know that it's more likely that the x-band on the stealths will get a track before a bunch of l-bands will either, I think that would depend on the power output of the various radars. If the L-bands are powerful enough then it could be that they'll get the track first. But of course if they can get a track at all, at a respectable range then the 4th gens will have levelled the playing field considerably.

I agree that there are real questions about whether the L-band radars will ever be fitted in sufficient numbers to make a difference. They most likely scenario (I think) is that they'll outfit four or five aircraft per squadron with the kit and that those aircraft will then act like a distributed mini-awacs for the rest of the formation, passing any tracks around via the network. The other planes in the formation can then use those tracks to cue other sensors or even fire weapons and guide them to the track via data-link. Even if the box is pretty big that those weapons get fired into I doubt that a F-35 or F-22 driver will just sit and watch them close on his position without reacting. At that point things will start getting complicated.

Maj. Gumbrecht recently said EFs came as close to F22 as 20 miles in BVR setup.
I'd imagine that's uncomfortably close for an F22 pilot and within heart of envelope of most IRSTs and MRAAMs.
Stick IR head on MRAAM and you put F22 pilot in a trouble, almost as bad as the one nonVLO platform is in, with the difference F22s will almost always be outnumbered.
The problem is stealth planes are so expensive today, that they still prohibit owning numbers required to actually impose LO technical superiority...well, at least according to USGvt.'s cost reports on F22/35.

USAF can maintain nonVLO fleet to supplement its VLO fleet, but what about AFs that can't and go for a single (VLO) type?
Who'll supplement them?

You are assuming that they have the radars pack in close enough to provide that kind of overlap. From what I have seen that is simply not the case.

pants3204 wrote:How vulnerable is the F-22 or any VLO aircraft to RCS degredation due to L-Band radar usage?

How effective is an L-Band radar in the leading edge of an aircraft (a la T-50)? Ground based L-Band?

As mentioned by others, L-Band radar is good for search but not tracking and fire control. The antennas on them are large and cumbersome and won't be easily transported. The low resolution they would provide to the operator is detrimental to the tracking and ID function. These large sites will only give away their position to the Raptor and the F-22 could just reposition itself if it picks up an L-Band radar turning on. The F-22 should still be quite difficult to detect with this radar type and I believe it's been tested against L-Band during RCS testing. As a result of poor mobility and angular resolution relegating it to a ground-based static search radar, the raptor could use its Alr-94 to pick it up and get away from it.

Leading edge L-Band radars are poorly designed for height determination of aircraft so in that respect you can only get bearing and range which is a lot less useful when painting a SA picture of the battlefield.

If the L-Band radar doesn't have the ability to determine altitude, wouldn't that mean that it has to work in Doppler mode -- only detecting aircraft by their radial motion relative to the ground?
That would tend to imply that, if you know the direction of the radar, you could turn right angle to it an cause it to loose you.

All modern fighter radars work on the "pulse doppler" concept, where velocity is determined based on the frequency shift of the radar returns (like you said). This is useful because it lets you sort out moving targets in ground clutter by discounting the returns that have no frequency shift (ie the ground or something moving tangent to the radar). Going to the "notch" takes advantage of this by reducing the doppler shift to the point that the evader is lost in the ground return and doppler ambiguities. Long story short, yeah you can probably break a lock on an L-band azimuth only radar by notching, but the same thing works with most other radars too.