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HFSS, Momentum simulation differences

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alffnot

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hi, i am new to learning HFSS so i am designing a directional coupler with microstrips and simulating in momentum and comparing the simulations in HFSS to see if i am using HFSS right.

i designed the directional coupler to couple at at -10 db, simulated just using ADS and give me exactly -10db, simulated using momentum it gives me -11.5dB. using same exact substrate, widths, etc and HFSS gives me a coupling of -8.5dB. is this typical, i have tried changing port size in HFSS, radition boundry and and just about every parameter i can find in the solution setup. and the results stay about teh same.

i'm kinda stuck, i can't seem to figure out what it could be, any ideas would be appreciated. thanks
 

itaifrenkel

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Hello,

1) Have you checked the solution convergence ?
From the project manager right click Results>Solution Data>Convergence
2) Solve ports only (checkbox in solution setup) and make sure the Z0 is correct. If it is not, increase the port accuracy (default 2%, highly accurate 0.2%) from the setup.
Then, remove ports only and simulate again.
3)Your wave port must touch the MS ground and extend into the area above it (roughly 5 times the height of the diel layer). In addition it should be wide (roughly 6 times the width of the MS).

Please add a gif with a snapshot of the model, maybe I'll have more ideas...

Itai
 

    alffnot

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alffnot

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thanks for the ideas, i hadn't noticed that it didn't converge, i had it set at maximum of 10 passes and it still didn't converge. i just moved it up to 20 and it took 12 passes to converge. that made the results move closer towards the momentum results but still a prett good difference. if you have any time could you take a look at my file and see if you notice anything i should change, if you can't that is alright.

in this design i moved the traces apart from about 39um to 50um and compared with momentum again, momentum gives about -12.5dBcouling and HFSS gives about -10.2dB. hopefully you can find something simple that i am doing wrong. i have put alot of hours into learning this program this week and it is getting frustrating
 

haydar

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what does solve only ports means?
I need only S parameters.
thanks.
 

EdmundZheng

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I think the different results between the different simulations are so normal, in fact, they are only simulations, they are just reference for the designs. sorry for my poor English! Best regards!
 

alffnot

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EdmundZheng said:
I think the different results between the different simulations are so normal, in fact, they are only simulations, they are just reference for the designs. sorry for my poor English! Best regards!

hopefully, i just want to make sure i am doing things right in HFSS since it seems like kinda a hard program to learn. just using the comparisons to judge if i am doing it right
 

alffnot

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if you look up a few posts from here i uploaded a link to my model. if you got a few minutes take a look and let me know if you see anything wrong. thanks
 

EdmundZheng

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^_^ i can't download anything, because i have not enough points!
best regards!
 

haydar

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you can download.
due to low storage, you will download that file without points.
you can see this under the download window.
 

EdmundZheng

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I think it is all right. But I am not sure whether you should set the differential and common mode on both ports or not. you didnt set.
 

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