Hi researchers , I have a Double Ridged Horn antenna design works between 0.6-3 GHz perfectly. I use CST 2017 and frequency range setting is 0.2 to 3GHz. But when I change the frequency range 0.2 to 1GHz or 0.2 to 2 GHz, S11 graph change. Why this happens I use the same antenna?
I don't know why this might happen. It is a bit surprising.
Did you use the same mesh?
I would expect CST to give less accurate results at the band edge because the excitation is small there (so it normalises by dividing by a small number), but your results are different over a wide range.
Malcolm White Yes , I realized the mesh was different maybe thats why the results were so different.
That may make some difference but I hope not that much!
The difference between -6dB and -12dB S11 is huge.
-8dB to -10dB isn't so much but still I'd expect a lot better of CST. I hope there is a good reason for the difference and we can sort it here so I can avoid the same bad kind of results.
It may be because of the large amount of energy that is in the cut-off region (37% of the frequency range up to 1 GHz) . Maybe if it started at 0.4 GHz the results would be closer.
It tends not to like having large amounts of energy bouncing about that it can't do anything with.
You will find relevant useful information in the following paper:
Article Eight-Element Compact UWB-MIMO/Diversity Antenna with WLAN B...
Yasin Hoşgör , because it's depend on your antenna design. The optimization depend on the operating frequency to the respective S11 and other antenna performances.
when u do measurement also, the S11 will be more significant for the respective operating frequencies.
Dear Yasin Hoşgör ,
welcome!
It is most probable a calculation error because of different sizes of the mesh in the three cases. I think the mesh size is related to the smallest wavelength.
As a matter of verification you can reduce the mesh size as that set in the third case .2 to 3GHz.
For the mesh size one has to reduce it till the solution stabilizes.
Best wishes
You can set adaptive mesh refinement in the set up solver window, and it will keep solving and then reducing the mesh until two solutions are close enough together.
I expected you would have done that already.
I am not sure how it is in CST, but traditionally solvers optimize the mesh for one frequency. So it is possible that your optimal frequency (upper limit ?) changes, and the distanced results change as well. Try improving the convergence options, and it should converge.
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