hfss filter design

Hello guys,

I haven't found any good examples of Microstrip filters (they were not exactly the same) designed in HFSS to base my project in, so I'm having a couple of problems, principally with the ports.

It's a very basic Chebyshev low-pass-filter, so It mustn't be very difficult. However, I'm having problems with the S-Parameters, which are not matching the theoric ones.

I would be very grateful If you could have a look at mi design. It only will take you a moment. As I have said, my doubts lie on the way ports are defined. I don't know if they are correctly set up.

Thanks you in advance ;)

Hi Chicoteleco, I am spanish too, where are you from? I am working on Microstrip structures right now too, maybe we could exchange knowledge. I am using CST-MWS but maybe I can help you. Please PM me or email me. See you!

Hello Pepillo, I've sent you a PM

I need help guys... I have done a lot of tests but I am having the same problems...

I simulate the structure but I obtain the S11 parameters which you could see (in blue) at the attached picture. It's like all was reflected. In red, the S12 parameter, that is completely wrong and incoherent.

I think the problem is that HFSS doesn't consider my second port and, obviously, all the EM is reflected.

So, my question is: I must the define my "exit port" in the same way as the excitation port (This is, a "Wave port" normalized to 50Ω)?

Thank you guys in advance

PD: I attach also the latest version of the design, If someone wants to have a look at it I would be very grateful

Chicoteleco, I have replied to your PM.

It looks like you have placed vias on both edges of the filter. That is, it is short-circuited to the ground plane on both sides. Is that correct on your design?

You can send me the parameters of your problem so that I can try to solve it with ADS, as I told you in the PM this tool is great for this kind of planar structures. I can obtain the S-parameters, surface currents and so on if you tell me what exactly you need to obtain.

Hello Pepillo,

I think It's not short-circuited because it's not a conductive surface. It's only a surface created to define the excitation at the entrance of the microstrip (also at the exit).

I took this "idea" from one planar design I found on this forum, so I don't know if it is 100% correct...

Thanks

Maybe you should try these:

- Remove those shortcuts (at least the one in the input port)
- Place a waveguide port at one end and another one at the opposite.
- Use just port 1 (input port) for computing S-parameters, maybe setting different "weights" at each port for excitation to null the 2nd port (i took this from ADS, where you state which port is used as input and wich one as output when displaying surface currents, for example).

I have replaced the mentioned surfaces by a "wave port" placed directly in the face of the box substract that is perpendicular to both ground plane and microstrip (I think I saw this way of exciting the structure on a HFSS video tutorial).

The results are the same... I don't know what more can I do... :(

You should surrround filter by the radiation boundary. In your example model is surrounded by pec from all sides including the surface where fillter lies. See my files... The size wave port must be large enough to accept all incident power.

I can't open the files, HFSS gives me an error. Maybe it's due to different versions... I have the 9.1.

I used to think that radiation boundary was only needed for calculate radiation patterns of antennas...I'm going to try to create one.

Thanks

It is needed to absorb energy. I have HFSS 10... Try to find it...
Try with radiation boundary or PML if with no succes i'll try to make new models.

I did your design, corrected some things

The problem was, certainly, the absence of the radiation boundary!

Thank you a lot guys! :D :D

Why you left vacuum below the ground plane?

the spurious EM fields going all around the structure that has been encountered by extending the radiation boundary

this is helfful

first to this page ！！

Hey jallem hope u r doing good. I have a question about the design that what is the thickness of copper. and also why you assign radiation to vacuum box. I think PEC is only for ground. kindly reply me. regards.