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Eigenmodes - Corrugated horn cavity

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Aug 19, 2009
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corrugated horn

Hi everyone - my first post :)

I am just getting to grips with CST and have to date only used the FDTD Transient Solver to solve the S-parameters for some corrugated horns. One of the projects I'm working on is determining the cavity or eigenmodes of horn to horn coupled systems. The purpose is to determine the round trip component that is sustained with a horn to horn cavity that may be responsible for any standing waves present in the system. Some of these eigenmodes have already been determined using an analytical mode-matching method, but I am hoping that we can get some validation from CST. I have created a simple system (attached) that has two corrugated horns facing one another with a small vacuum cavity between them (they are actually two full length 100GHz horns that have been pared down to their first ten corrugations - this is to save computation time for the time being). At the moment I cannot get anything sensible from the Eigenmode solver and I need some help:

1. Does a system like this make sense in the CST eigenmode solver environment? The waveguides at the backs of the horns are open - should these be closed with an absorber material of some sort to represent power coupled to the receiver?

2. How exactly does the eigenmode solver work? I can't find any reference to the exact method. When using the Transient Solver I needed to input a waveguide port, but why is that not needed here? In what way are the eigenmodes determined? What kind of source fields are used, if any?

3. I am unsure of which solver to use though I think that since the system may be considered lossy I am using the JDM solver. Is this correct?

4. Is it possible to determine the eigenmodes within the system purely within the defined operating frequency range of the system? Using the AKS it seems to generate eigenmodes of much lower frequency.

4. Is it possible using the eigenmode solver to determine the reflected and transmitted S-parameters of the system?

5. Is it possible to output these eigenmodes at a particular location?I know that I can view them but I was hoping to be able to compare them to those that have been determined analytically.

I hope that someone will be able to help me out here - constantly running such systems over long hours with indefinite results is very time consuming :(

Yours in eigen-distress


Has anyone had any ideas about this problem yet?

Did you try this kind of simulation in HFSS?
I mean what kind of output/results you are looking for?
Did you check CST help for these questions?

Hi Abhishekabs - thanks for replying :)

Unfortunately we havent got HFSS here (yet), and the CST help is not very forthcoming on what the exact process of how the eigenmodes are determined.

I suppose that I am looking for the resonant beam shapes/power profiles that are sustained between the two horns, i.e. the power that does not couple from receiver to transmitter. The idea here is to compare the predicted 'eigenmode(s)' with those as we have determined through a mode-matching eigenvalue tracking process. The idea is to possibly, through an iterative process to produce a less resonant horn to horn cavity.

If there is any light you can shed on the eigenmode solver process wrt this problem I would be very grateful

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