Hi,
About a year ago I read that Aesa can detect the number of blades on the jet engine----determing what kind of engine it is---thus what kind of aircraft and how many---even if they are flying real close---I lost that article somewhere---. What is your input on that! Thankyou.
While the superiority of even the basic ESA system is undisputed and that the ability of an AESA system to create a beam width that -- in theory -- could do what is claimed, I would reserve judgment on that claim. The issue here is complex...
- The amount of reflective surfaces that are available for any pulse in any time period.
- Beam dispersion or 'widening'.
- Moving surfaces.
A series of pulses is called appropriately enough a 'pulse train'. A jet engine will have several stages of moving blades. A pulse train will exhibit different behaviors on a
SINGLE blade because the blade itself is not an ideal geometric figure like a sphere, which exhibit predictable reflective behavior regardless of approach angle, but that the blade will have edges and curves, which will induce different reflective signal behavior. Beam widening because of increasing distance lead us back to the resolution cell property which could make a pulse train to believe two or more blades as one.
Finally there is interference...
Simulcasting
You can think of the two radio signals as waves, with peaks and troughs as they travel from the transmitter to the receiver. If the content of the two signals is the same and the signals arrive at the receiver at exactly the same time, the peaks and troughs will match each other and the two signals will reinforce each other. In this condition the signals are described as in-phase and result in constructive interference. Most receivers perform very well with this positive type of interference.
However, if the content of the two signals is the same but the signals do not arrive at the receiver at the exact same moment, the peaks and troughs won't match up. This condition is known as out of phase and results in destructive interference.
Both types will occur at any point in time in any pulse train precisely because of the moving blades -- in multiple stages at that. And keep in mind that the aircraft is moving as well.
So while under ideal conditions, aka laboratory, we can take static measurements of a jet engine and compare it against known signatures, similar to sonar signatures, and make a reasonably accurate declaration that we are looking at the radar signature of so-and-so engine and therefore at a so-and-so fighter, applications under far less than ideal conditions may not make the attempt technically and financially worthwhile.