HFSS Eigen mode solver and driven model
I am designing a coupler which has to be over coupled as a part of my project.
I used Eigen solver with PML as boundary condition and based on loaded Q value and field in cavity successfully found the exact coupling slot at the resonant frequency. From this value of coupling I can very easily calculate s11 and I know the frequency.
Problem is when I try to simulate the same model using HFSS driven model with PML replaced with port I do not get anything at that frequency even frequency sweep does not return anything while the filed inside the structure is exactly the same as calculated with Eigen Solver.
I am sure I am doing something wrong but I need to know.
Thanks in advance for help
What mode(s) is/are your waveport exciting?
Thanks a lot for your response.
I have tried to attach screen grab of model, field configurations which may be needed to look through the problem. But if something is missing let me know
Model:
E_field_driven_model:
Eigen_Solver_Solution:
E_field_Eigen_solver:
E_field_port:
Where is the PML? Or did you mean PMC?
No when I say PML I mean PML.
It is defined in place of PORT in Eigen solver while in driven model it is replaced with PORT.
Screen grab is attached
In previous post you can very clearly see that coupling is there and field is identical in case of both Eigen and driven model.
Point is if coupling is there why s11 I get is not matching to coupling and that calculated with Eigen solver in case of driven model
Ok, I see. Yes, the fields are the same.
I'm not sure if the quality factor (Q) of the mode (from your eigenmode simulation) is strictly related to S11. The quality factor of the mode deals with energy that is already contained by that mode, whereas the S11 deals with the matching between your excitation source and that mode. I would expect them to be the same if there was perfect mode matching, but do you know that is the case?
Update:
In fact, reviewing your images, it seems that the eigenmode fields go to zero at the PML (where your waveport should be). Is your wave port exciting such a mode? (Are these magnitude fields at a certain phase, or complex magnitude fields?)
I am attaching screen shot of answer to your first part
Just have a look at the corresponding curves of s11 for under over and critical coupling case.
I am not expecting s11 to be around -40 dB as is the case in critical coupling as I am trying to be over coupled but even in this case I must get some decent s11 curve.
About the second part I am not very clear what you are asking but let me explain my side correct me where my understanding is wrong about driven model
1. We define port as source of excitation.
2. Modes excited in the structure are driven by port
3. So it means the field excited in the structure is due to the port.
4. Filed in the structure is correct and we can see coupling
5. what is then wrong with s11
If there is indeed coupling between the excited and resonant modes, then the return loss must be coming from elsewhere. Is your aperture segment well-matched between the feeding waveguide and the cavity?
Is your cavity lossless? I can't see this helping things, although I'm definitely not an expert on cavities.
What is the S11 value you get compared to the theoretical?
Lets make things simpler
1.Coupling coefficient is called Beeta
2. If Beeta = 1 it means we are critically coupled and mag(s11) = 0
3. If Beeta < 1 it means we are under coupled and 0 < mag(s11) < 1 with small BW
4. If Beeta > 1 it means we are over coupled and 0 < mag(s11) <1 with large BW
5. Slot size defines the coupling bigger the slot the stronger the coupling is
since we are over coupled by a factor of 10 so mag(s11) should be around 0.8 with reasonable BW.
It is nothing specific to cavities it is just coupling