Understanding Radar Signature Data

[obrien979]

I am struggling to understand the Radar Signature information for Aircraft. I am probably overthinking this and have missed the boat somewhere. Based on the photo attached, it appears that the F-117A has a lower radar picture then the newet F-22 Raptor. Meaning that it is more stealthier when up against A-D Band Radars and more likely to be seen using E-M Band Radars. Am I correct on this?

[Dragon029]

Radar signature is measured in dBsm, which is a decibel / logarithmic scale. To convert from decibel square metres to normal square metres, you use the formula:

area in square metre = 10 ^ (dBsm / 10)

Then to convert an area in square metres back into dBsm, you use the formula (where the log is using base 10):

area in dBsm = 10 x log(area in square metres)

Due to the nature of logarithms and powers, the more negative a value is in dBsm, the smaller an area it represents.

So according to that chart (which is going to be speculation or from an incomplete simulation keep in mind), the F-117A has an average radar signature of -14dBsm in radar bands A-D, which roughly equals 0.04m^2, and a radar signature of -24dBsm in radar bands E-M, which roughly equals 0.004m^2.

The F-22 meanwhile apparently has an average radar signature in the A-D bands of -20dBsm or 0.01m^2 (4x smaller than the F-117), and an average radar signature in the E-M bands of -30dBsm or 0.001m^2 (again 4x smaller than the F-117).

[obrien979]

ORIGINAL: Dragon029

Radar signature is measured in dBsm, which is a decibel / logarithmic scale. To convert from decibel square metres to normal square metres, you use the formula:

area in square metre = 10 ^ (dBsm / 10)

Then to convert an area in square metres back into dBsm, you use the formula (where the log is using base 10):

area in dBsm = 10 x log(area in square metres)

Due to the nature of logarithms and powers, the more negative a value is in dBsm, the smaller an area it represents.

So according to that chart (which is going to be speculation or from an incomplete simulation keep in mind), the F-117A has an average radar signature of -14dBsm in radar bands A-D, which roughly equals 0.04m^2, and a radar signature of -24dBsm in radar bands E-M, which roughly equals 0.004m^2.

The F-22 meanwhile apparently has an average radar signature in the A-D bands of -20dBsm or 0.01m^2 (4x smaller than the F-117), and an average radar signature in the E-M bands of -30dBsm or 0.001m^2 (again 4x smaller than the F-117).

Thank you for this outstanding explanation in Layman's terms. I think I have an understanding of this now. I suspected that the lower the negative value, the better its stealthiness. Time to put this new knowledge to test on some missions.

[c3k]

Or, in simpler terms, the more negative the value, the LESS energy gets reflected BACK to the radar antenna. You want a BIG REDUCTION in energy being reflected back to maintain stealth.

[SeaQueen]

Electrical engineers like to work in decibels (dB) rather than simpler to understand linearly scaled units. The reason is that when you measure things on a logarithmic scale (i.e. dB) small changes in the underlying quantity that don't matter much get washed out. In that sense, dBsm are actually a much more convenient way of measuring rcs.

Code: Select all

 rcs (m^2) | rcs (dBsm)
 ------------------------
 1000      | 30
 100       | 20
 10        | 10
 1         |  0
 0.1       | -10
 0.01      | -20
 0.001     | -30