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I'm using the HFSS SBR+ solution type. I have one PEC sphere and two parametric beam antennas. I am trying to find out how much S parameters change with the Doppler effect. enter image description here Configuration:

Range Resolution: 1 m
Range Period: 200 m
Velocity Resolution: 0.4 m/s
Velocity Min: -2 m/s
Velocity Max: 2 m/s

Keeping every other thing the same and just changing the velocity, I don't get any different results. Even if I make the velocity 2000 m/s which is too high, I get exactly the same result as 2 m/s. Am I doing something wrong? Or S parameters don't change with velocity?

merovingian
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2 Answers2

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The speed of light is 299,792,458 m/s. For 2 m/s vs 2000 m/s is almost a basically a rounding error with regards to the doppler shift.

mgwalker95
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    So how does doppler radar routinely discriminate velocities on the order of 0-50 m/s? – The Photon Dec 10 '22 at 15:53
  • @ThePhoton Doppler typically uses heterodyne detection where the received signal is downmixed by the transmitted signal, so what counts there is the absolute difference (in Hz) not the relative difference (in percent). For scattering it is the relative difference that counts, so for non-relativistic speeds scattering doesn't change. Fun example of how powerful heterodyne detection is, I once built a relatively simple system that used an NIR laser to detect a 1mm/s velocity based on Doppler shift, a difference of 1000 Hz on a 300 THz laser, or about 3 parts per trillion! – user1850479 Aug 12 '23 at 00:29
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Scattering parameters will stay constant, for constant frequency, which will remain constant within same frame of reference - your HFSS model.

In you model, PEC sphere at 200 m, is probably (frequency is not declared) in the far field. Only far field parameters might have some (minor) changes, dependent on phase/frequency shifts induced by movement, but those shifts are almost invisible in lobes calculation and probably invisible in scattering parameters (limitations of calculation precision).

Danko Dnevic
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