[REPORTED]Radar Elevation Coverage

Not sure if my understanding is correct or if there is an actual bug, so I am posting it to cross check with others before reporting it.

I measured in the simulation the radar elevation coverage for various ranges and bars in the F-16 and F-18, checking the number on top and bottom which represents the maximum and mininum altitudes covered at 20nm, 40nm and 80nm.

[TABLE=head]Aircraft|Bars | 20nm | 40nm | 80nm

F-16 | 1 bar | 1 | 1 | 1

F-16 | 2 bar | 9 | 18 | 36

F-16 | 4 bar | 28 | 56 | 99

F-18 | 1 bar | 1 | 1 | 1

F-18 | 2 bar | 6 | 11 | 22

F-18 | 4 bar | 16 | 32 | 64

F-18 | 6 bar | 28 | 56 | 99

[/TABLE]

First thing that struck me is that, in 1 bar scan for both the 16 and 18, the elevation caret displays a single number and does not change in value regardless of distance. Shouldn't it be increasing in coverage the farther from the aircraft?

The only public reference I found on the APG-68 beamwidth is a PDF from the University of Tenessee which states 3.25 deg for azimuth and 4.55 deg for elevation. I assume the beam is oval-shaped as it follows inversely the shape of the antenna. Therefore at 20nm the beamwidth would be aprox. 9655 feet, which is close to the value that the simulation actually exhibits for the 2 bar at 20nm. Therefore I would expect to see the coverage for the 1 bar scan be the same as the 2 bar scan is presently.

Given that F-18 APG-73 antenna is circular, I would assume its beam in elevation is 3.2deg as literature describes, and therefore at 20nm its coverage would be aprox. 6700 feet. Again, in the simulation this is the value displayed for a 2 bar scan, so I believe these values are correct but should be in 1 bar instead.

Now for the 2 bar scan things are more complicated because there should be some overlap between the bars, so it wouldn't be just the double of 1 bar scan. I couldn't find information for the F-16. For the F-18 there is a CNATRA PDF which shows 10k feet of coverage at 20nm for 2 bar scan, which implies an overlap of 50% between the bars, assuming that 1 bar would be 6700 feet. If this is true, then at 20nm 4 bar should be 17k feet and 6 bar should be 24k feet.

Applying the same overlap between bars to the F-16, it should have 14k feet at 2 bars/20nm and so on.

I calculated what the values *should* be in the table below:

[TABLE=head]Aircraft|Bars | 20nm | 40nm | 80nm

F-16 | 1 bar | 9 | 19 | 38

F-16 | 2 bar | 14 | 28 | 57

F-16 | 4 bar | 24 | 48 | 96

F-18 | 1 bar | 7 | 14 | 28

F-18 | 2 bar | 10 | 21 | 42

F-18 | 4 bar | 17 | 35 | 70

F-18 | 6 bar | 24 | 49 | 98

[/TABLE]

And here are the differences between my calculations and the simulation. Note the huge increase in coverage in 1 bar, moderate increase in 2 bar for F-16 and 2/4 bar for the Hornet, and slight decrease in 4 bar for the F-16 and 6 bar for the Hornet.

[TABLE=head]Aircraft|Bars | 20nm | 40nm | 80nm

F-16 | 1 bar | +8 | +18 | +37

F-16 | 2 bar | +5 | +10 | +21

F-16 | 4 bar | -4 | -8 | -3

F-18 | 1 bar | +6 | +13 | +27

F-18 | 2 bar | +4 | +10 | +20

F-18 | 4 bar | +1 | +3 | +6

F-18 | 6 bar | -4 | -7 | -1

[/TABLE]

Now some other factors to consider:

I did not test the radar actual detection coverage, I just checked the numbers in the radar scope itself. It could be that the numbers are wrong but the coverage is working, but I never noticed picking up contacts outside those numbers so I doubt it is the case. But it should be tested.

There could be a fundamental error in my understanding, for which I ask the community for help in pointing out. I double checked the numbers and the theory and they seem to match.

There could be other factors that change the radar coverage - for example, the overlap between the bars could be different between 2 bar vs 4 bar vs 6 bar. I haven't found any info that indicates this, but lack of info does not mean lack of existence.

If this checks out, then other aircraft which implements air to air like the F-14 and Mirage could suffer also from this problem. I would verify them once / if these calculations turn out to be correct.

So what do you guys think?

Great information, I wonder if these figures match the information ED is using for the radar simulation.

Typically elevation bars are separated by 1/2 the antenna's elevation beamwidth. Though they are sometimes made to be just slightly closer.

See my example below

Thanks Beamscanner, always like your posts on stuff like this.

Typically elevation bars are separated by 1/2 the antenna's elevation beamwidth. Though they are sometimes made to be just slightly closer.

 

See my example below

Great, it checks out with my calculations and the CNATRA document then.

I've revised the initial post to correct for rounding (rounding down to thousands of feet instead of rouding to nearest) and a typo (I said before it was 25% overlap between bars, should be 50%).

After more searching of the internet I've also found an old HAF F-16 manual which contains elevation figures that match what I've got, however I am not sure if ED could use it as a source. However I will submit it now as a bug report for both the F-16 and F-18.

Excellent research done here. I always have been wondering about the 1 bar coverage, but probably it's just the displayed number that's off.

Great, it checks out with my calculations and the CNATRA document then.

 

I've revised the initial post to correct for rounding (rounding down to thousands of feet instead of rouding to nearest) and a typo (I said before it was 25% overlap between bars, should be 50%).

 

After more searching of the internet I've also found an old HAF F-16 manual which contains elevation figures that match what I've got, however I am not sure if ED could use it as a source. However I will submit it now as a bug report for both the F-16 and F-18.

I am fairly confident they do use the HAF manual as a source, because of mistakes such as stating the comm switch has IFF functions and TMS left = expanded data on radar page which is not correct for USAF CM vipers (they ended up correcting themselves and now TMS left = IFF interrogate).