different result in FEKO HFSS and CST
Altair EmployeeHi,
Hope everybody are good.
Please find attached full question with diagrams.
A coax-fed patch antenna with dimensions given in table below, is simulated in HFSS, CST and FEKO
softwares.
It is seen that:
The results of the CST software in the case of
- The phase Z component of the electric field on the line parallel to y axis
and
The results of the FEKO software in the case of
- The magnitude of X component of the electric field on the line parallel to y axis
- The phase of X component of the electric field on the line parallel to y axis
- The phase of Z component of the electric field on the line parallel to y axis
- The phase of Z component of the electric field on the line parallel to x axis
and
The results of the HFSS software in the case of
- The phase of X component of the electric field on the line parallel to y axis
- The phase of Z component of the electric field on the line parallel to y axis
are completely different from the results of the two other softwares (despite partial similarity of the field
behavior in other cases).
The question is why it is such different.
Answers
-
Dear Susanne
Let me start with some general comments on your results. For both HFSS and CST we see that the (near) field results are not smooth. There are spikes and jumps. While I am not an expert in using these codes, I suspect that this is caused by the volume mesh elements being too large. As the volume elements represent the fields, more, smaller elements would be required to accurately represent the fields.
In the FEKO model I assume you used the default Surface Equivalence Principle (SEP). This models surface currents and then integrates over these to obtain fields. This then does not require volume elements surrounding the patch and results in smoother field results.
To comment on your specific results:
- The magnitude of X component of the electric field on the line parallel to y axis
Here it appears inaccuracies in the HFSS and CST results result in spikes with magnitudes in the order of 1 to 2 V/m. As suggested above, this might require more accurate modelling in these codes.
The smooth and much smaller field component values as obtained by FEKO is expected and should be considered as correct.
- The phase of X component of the electric field on the line parallel to y axis
Based on the incorrect fields values as seen in the magnitude, also the phase for the HFSS and CST results would be incorrect.
- The phase of Z component of the electric field on the line parallel to y axis
Here we simply have different representations of the same phase performance. The HFSS and CST results appear to be “flipped”. This might simply be a different in what is considered the positive Y direction in your models.
The FEKO graph has not been “unwrapped”. This results in the expected “jumps” at 180/-180 as the phase is expressed as a value between + and – 180 degrees. In POSTFEKO you can select the “unwrap phase” option to show the phase as a continuous trace.
I believe that the FEKO result with the “unwrap phase” option should then show exactly the same curve as the CST result, but only with a 90 degree offset. We see this same 90 degree offset in the other phase results. This appears to show that HFSS and CST have their excitations as a cosine wave (starting at a peak value at phase=0 degrees) while FEKO uses a sine wave (starting at a zero magnitude at phase=0 degrees). You can set a different phase for the excitation in FEKO if required.
- The phase of Z component of the electric field on the line parallel to x axis
In this case the HFSS and CST results show the jumps from +180 to -180 due to the phase being wrapped. The same comments as above apply.
Kind regards,
Johan H
0