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.

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.

Can I please get some feedback on why this issue might be occuring and how I can fix it?

Thank you,

Shyam