J-20 5th Gen Fighter Thread IV (Closed to posting)

[Insignius]

Oh, yes. I overread that angular degree. Anyway, vertical denotes dbsm values without mistake, so the question is now at what band these values are.

 

[no_name]

Are we sure it's wavelength and not an angular measurement? The graph labels that axis as degrees.

And I'm pretty sure the measure is only for the canard itself. The description only mentions seeing corner, and It's not unusual for small changes in geometry to generate large differences in RCS.

Plus one needs to remember that even a -16 dbsm return would be representative of the real thing, just the rcs performance of the geometry. The real thing would still have RAM, especially on the edges.

The horizontal axis denotes phi degrees, which would be varying angle on the horizontal plane. I would guess they used the same frequency as fighter radars. But this still does not tell us a lot - like the position the canard is it for example.

The wiggles in the plots are due to multipath effects. So whereas before in the middle of the plot you have significant contribution to RCS from that sharp corner, now you have two less sharp ones and they together gives back less return than that single one, and because there are two components of similar value, you get alternative phase additions/cancellations as you move around the horizontal plane.

 

[vesicles]

Oh, yes. I overread that angular degree. Anyway, vertical denotes dbsm values without mistake, so the question is now at what band these values are.

yeah, we need the complete paper...

 

[no_name]

You Still Cannot See A Thing!

I am not sure but I think they may have shaved the edges here circled in red also:

They also seems to be of a lighter grey colour - placement positions for back looking sensor/PAR?

Second look seems like it is just different colour.

Also the centre part in between the nozzles changed too?

 

[latenlazy]

The horizontal axis denotes phi degrees, which would be varying angle on the horizontal plane. I would guess they used the same frequency as fighter radars. But this still does not tell us a lot - like the position the canard is it for example.

The wiggles in the plots are due to multipath effects. So whereas before in the middle of the plot you have significant contribution to RCS from that sharp corner, now you have two less sharp ones and they together gives back less return than that single one, and because there are two components of similar value, you get alternative phase additions/cancellations as you move around the horizontal plane.

That's kinda what I thought was going on when I looked at the graph (without as much of the technical understanding). Thanks for the explanation.

 

[T-U-P]

Oh, yes. I overread that angular degree. Anyway, vertical denotes dbsm values without mistake, so the question is now at what band these values are.

In aircraft terms phi would be the roll/bank angle of the plane.

 

[no_name]

I think though, that the phi here is for theta-phi coordinate system that they are using to measure received signal.

Theta traces out vertical semicircle. phi traces out the horizontal 360 degree circle, together they describe any point on a spherical measurement surface enclosing the test object at a certain set distance.

Sometimes the result is displayed as a horizontal circle plot and vertical circle plot. You get those for antenna radiation pattern sheets.

So in this plot I would say it is implied that theta is 90 degrees(from the pos z axis pointing vertically).

 

[latenlazy]

I think though, that the phi here is for theta-phi coordinate system that they are using to measure received signal.

Theta traces out vertical semicircle. phi traces out the horizontal 360 degree circle, together they describe any point on a spherical test surface enclosing the test object.

Sometime the result is displayed as a horizontal circle plot and vertical circle plot. You get those for antenna radiation pattern sheets.

So in this plot I would say it is implied that theta is 90 degrees(from the top).

It might make more sense if theta is 0 degrees. After all, that's probably the vertical angle they're most interested in and where the clipped corners have the biggest impact.

 

[no_name]

It might make more sense if theta is 0 degrees. After all, that's probably the angles they're most interested and where the clipped corners have the biggest impact.

So you mean looking at the canard from directly above?
Or are you thinking of theta as going from -90 to 90 degrees? - because they go from 0 to 180 top to bottom according to convention, so horizontal plane would lie theta 90 degrees.

 

[davidwangqi]

Phi should be the azimuthal angle which here I assume stands for the horizontal incidence/reflection only. The result must be based on a single piece of canard only due to the asymmetric curves. Interesting thing is for -5 degree < phi< 0 degree which means other side of the clipped corner, the RCS improvement is still very noticeable.

BTW, the hided part by watermarks is 3GHz, so S-band.

In aircraft terms phi would be the roll/bank angle of the plane.