bittu:
Yes, you should be able to analyze this in Sonnet. You can probably do it in Sonnet Lite. Since Sonnet has sidewalls, you have to make sure you keep them well away from the patch, like 1-2 wavelengths away, and make sure the top of the Sonnet analysis box has free space set for a top boundary.
You should be able to use a via port feed for a probe feed, and you can probably use a Parameter to control the location of the probe. If you are just on a diagonal, I think they will let you have a linked parameter for the X and Y dimension placement of the probe. Then you can let the software run sweeps of probe location and give you a family of design curves automatically. If you have a higher version of Sonnet, I think you could optimize the probe placement with the built-in optimizer.
Good luck,
--Max