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[SOLVED] How to optimize my S-parameters in the EM-Simulation Model

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DieBemme

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Hey everyone,

for a student project of mine, I am designing a hairpin filter, with a bandwith that can be controlled via a diode. The simulation in my schematic works wonderful and shows the expected behaviour.
It may seem kinda overloaded but the part I'm mainly struggling with is the layout (see further down).



1732115785795.png

1732115809257.png


Yet, after designing the layout (leaving proper space for lumped elements), naming the ports and defining the vias, the simulation result show a much worse "chebychev-kind" response. On one part the filter attenuation is way higher, and on the other hand I dont get such a clear passband, as one peak is more dominant than the rest... I hope you can give me some tips, on what I can optimize in my design to optimize my filter response.

This is the first time I am designing a microstrip filter and had a really great time playing with all the possibilities, but thought that you guys probably have way more experience and another viewpoint... Thx in advance!

And here the pics for the layout side of design:

1732116181956.png

1732116208815.png

1732116231400.png

1732116243318.png

1732116295949.png
 

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No answer to your question, but a hint for getting accurate results: for such coupled line designs, you need to enable edge mesh in Momentum settings.

EM-based optimization of planar filters is a research topic on its own. One of the guys who published a lot on efficient methods is Dan Swanson.
Here is one of his papers, this one uses Sonnet EM but you might get the idea:
--- Updated ---

Two more comments, in addition the edge mesh:

1) Having the open ends - where you have maximum E field - over a ground plane cutout is a big difference to the microstrip models that assume solid ground.

2) For the pins/ports on the middle of the resonator arms, make sure you have defined a port with (small) finite width. Placing a "dot" pin there is invalid, because the port will extend along the entire edge.

edgeport.png
 
Last edited:
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volker@muehlhaus said:
No answer to your question, but a hint for getting accurate results: for such coupled line designs, you need to enable edge mesh in Momentum settings.

EM-based optimization of planar filters is a research topic on its own. One of the guys who published a lot on efficient methods is Dan Swanson.
Here is one of his papers, this one uses Sonnet EM but you might get the idea:
--- Updated ---

Two more comments, in addition the edge mesh:

1) Having the open ends - where you have maximum E field - over a ground plane cutout is a big difference to the microstrip models that assume solid ground.

2) For the pins/ports on the middle of the resonator arms, make sure you have defined a port with (small) finite width. Placing a "dot" pin there is invalid, because the port will extend along the entire edge.

View attachment 195455
Click to expand...

Thanks for your quick answer, I will definetly try that out and take a look at the attached paper! :)

But regarding the ports: Is it useful to change all my pins from point to edge shape? Or only for those long edges?
 

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DieBemme said:
But regarding the ports: Is it useful to change all my pins from point to edge shape? Or only for those long edges?
Click to expand...
It is important for the long edges, because a "point" pin placed on the long edge would create port port width = entire long edge width.

Note that this happens only if the pin is straight on the edge, and there is no problem if there is a little "notch" standing out where the pin is placed. Looking at your layouts, you had such a notch in the original layout, but I don't see that in the meshed EM view. So I would enforce the desired port width at these locations by an edge pin with defined width.

If you have small components attached to the open end of your resonators, with component pad width much smaller than edge width, you can also use this method. It makes sure than your current flow in EM agrees with the physical current flow at these locations.
 
Last edited:

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The discrepency is too much between schematic and layout. I'm afraid this filter has not an appropriate layout for optimization.
There are many critical couplings and GND connections.Optimize all those stuffs is not easy by using simple optimizer.
 

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BigBoss said:
The discrepency is too much between schematic and layout. I'm afraid this filter has not an appropriate layout for optimization.
There are many critical couplings and GND connections.Optimize all those stuffs is not easy by using simple optimizer.
Click to expand...
So what you mean is that this filter can't rly be implemented in reality? Or that there is no simple solution for it's optimization?
 

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You can use some "tricks" to speed up tuning/optimization, as outlined in the paper that I linked above. You can tweak coupling between stages by adding a lumped C, which simulates the effect of changing gap width, and by adding a short MLIN segment at the open end, with positive or negative delta_length, to see the effect of changes to the resonator length. Both these tuning methods work at circuit simulator speed, without re-simulating the EM model over and over again, so it gives fast insight what direction to tweak the layout. In the end, after implementing the layout changes, you want to reach delta_C (additional C across the gap) = 0 and delta_length (additional resonator length) = 0.
 

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volker@muehlhaus said:
No answer to your question, but a hint for getting accurate results: for such coupled line designs, you need to enable edge mesh in Momentum settings.

EM-based optimization of planar filters is a research topic on its own. One of the guys who published a lot on efficient methods is Dan Swanson.
Here is one of his papers, this one uses Sonnet EM but you might get the idea:
--- Updated ---

Two more comments, in addition the edge mesh:

1) Having the open ends - where you have maximum E field - over a ground plane cutout is a big difference to the microstrip models that assume solid ground.

2) For the pins/ports on the middle of the resonator arms, make sure you have defined a port with (small) finite width. Placing a "dot" pin there is invalid, because the port will extend along the entire edge.

View attachment 195455
Click to expand...
Thank you SO SO MUCH!

I don't know which of these was the determining factor, but now my result looks like I want it to :)

1732282971436.png


Thanks for the help, and have a great weekend! :D
 
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