180 Degree Phase Shift When Measuring S21
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Hi,
I'm running a parametric sweep by rotating a probe around a central horn antenna. I'm showing a few images below for illustration.
Fig 1: At Theta = 0 degrees.
Fig 2: At Theta = 10 degrees
Fig 3: Theta = 20 degrees
...And so on...
When I measure the phase of the S21 results, I see random 180 degree shifts in the measurements. I am not able to see any pattern in these shifts either.
I thought perhaps it was because I was initially using 2 FE-BI boundaries and that might be causing an issue. So I tried a single Radiation boundary instead, but that also didn't help.
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theta_rotation [deg] S21 Phase Results [deg] -10 101.2924367 -9 103.7009139 -8 105.601412 -7 107.5837877 -6 109.0814497 -5 110.6225511 -4 -68.19983945 -3 112.7819268 -2 -66.46548137 -1 -65.96723292 0 114.1349591 1 114.08219 2 113.6846084 3 -66.93414481 4 112.1847997 5 111.1811682 6 109.7736687 7 -71.78552943 8 106.3168243 9 104.558732 10 102.4050767 As you can see from these results, at random points the phase shifts down by ~180 degrees.
For example at Theta = -4, the phase measurement is -68.2 degrees, whereas at Theta = -5 it is 110.6 degrees, and at Theta = -3 it is 112.8 degrees. The -68.2 measurement seems to be shifted down by 180 degrees (-68.2 + 180 = 111.8). 111.8 degrees seems like a more reasonable measurement. This occurs again at random points with no discernible pattern.
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Can I please get some feedback on why this issue might be occuring and how I can fix it?
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Thank you,
Shyam
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I recreated a small case for illustration:
2 antennas with rotation and febi:
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it also goes from -10deg to 10deg in a parametric sweep.
FEBI used at 3D component
mesh asembly used and mesh is preserved in the parametric sweep to avoidn numerical noise:
this looks correct.
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Hi David,
Regarding the radiation box, I meant I tried a single radiation box encapsulating both antennas, as well as a separate simulation where I had the two antennas in individual FEBI boundaries.
I am maintaining the distance between the antennas as I rotate. I have tried a short distance... actually the distance between the two spheres (the ones the antennas lie in) is 150mm. As I'm simulating at roughly 10GHz, the antennas are only about 5 wavelengths apart.
Regarding the convergence, I've taken a look, and it seems that the convergence from one adaptive pass to another can jump up by 180 degrees. If you take a look at the below image, at -10degrees, the simulation seems like it will converge near -79degrees, but then at adaptive pass 7 it shoots up by 180.
Convergence shoots up at pass #7, which is again where the change from -79 to 101 occurs as highlighted above, and then it settles back down.
And then if you take a look at the first image again and consider the theta_rot = -7degrees case, the value always remains around 110degrees for all 8 adaptive passes. And the convergence doesn't shoot up as we see in almost every other case.
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I see that you are not having the same issue as I am from the S-parameter plot you posted. So maybe I need to do something special regarding the mesh? I have not changed anything regarding the meshing from the default settings. I'm not quite sure what you mean by "mesh asembly used and mesh is preserved in the parametric sweep to avoidn numerical noise:". How can we use mesh assembly, and is it available in 2021.R1 version? And how did you "preserve the mesh in the parametric sweep?"
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Thank you,
Shyam Patel
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