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    Balun design gives box resonance error in Sonnet

    Why does this balun design (A 0.8–8 GHz Multi-Section Coupled Line Balun) give box resonance error in Sonnet ?

    Note: Just rename the attached Multi-Section_Coupled_Line_Balun.txt to Multi-Section_Coupled_Line_Balun.son will let Sonnet open it.

    Box Resonance Error

    Code:
    Box resonances estimated for: Multi-Section_Coupled_Line_Balun.son
    The estimated box resonance frequencies are listed below.
    The calculations assume lossless materials, with a box filled with
    only the specified dielectric stackup materials.
    
    6.226 GHZ  TM Mode 1,1,0
    6.941 GHZ  TM Mode 2,1,0
    7.006 GHZ  TE Mode 1,0,1
    7.718 GHZ  TE Mode 2,0,1
    9.009 GHZ  TM Mode 1,1,1
    9.153 GHZ  TE Mode 0,1,1
    9.341 GHZ  TE Mode 1,1,1
    9.492 GHZ  TM Mode 2,1,1
    9.884 GHZ  TE Mode 2,1,1
    
    Only lowest order modes considered.




    Multi-Section_Coupled_Line_Balun.son

    Code:
    FTYP SONPROJ 13 ! Sonnet Project File
    DIM
    FREQ GHZ
    IND NH
    LNG MM
    ANG DEG
    CON /OH
    CAP PF
    RES OH
    END DIM
    FREQ
    ABS 0.1 10.0 
    END FREQ
    CONTROL
    ABS
    OPTIONS  -d 
    SPEED 1
    CACHE_ABS 1
    TARG_ABS 300
    Q_ACC N
    END CONTROL
    GEO
    TMET "Lossless" 0 SUP 0 0 0 0
    BMET "Lossless" 0 SUP 0 0 0 0
    BOX 1 79.359277 23.997124 1250 378 20 0
          20 1 1 0 0 0 0 "Air"
          2 4.4 1 0.02 0 0 0 "FR-4"
    LORGN 0 23.997124 U 
    POR1 STD
    POLY 9 1
    3
    3 50 0 0 0 79.31161153 0.5693301799 
    POR1 STD
    POLY 13 1
    2
    2 50 0 0 0 58.93250351 23.99712339 
    POR1 STD
    POLY 25 1
    2
    1 50 0 0 0 1.146043145 23.98397036 
    NUM 18
    0 6 -1 N 9 1 1 100 100 0 0 0 Y
    79.31161153 -0.03337140237
    64.26069456 -0.03337140237
    64.26069456 1.172031762
    79.31161153 1.172031762
    79.31161153 -0.03337140237
    79.31161153 -0.03337140237
    END
    0 6 -1 N 10 1 1 100 100 0 0 0 Y
    64.26179217 0.3948257219
    45.64768726 0.3948257219
    45.64768726 0.7945943407
    64.26179217 0.7945943407
    64.26179217 0.3948257219
    64.26179217 0.3948257219
    END
    0 6 -1 N 11 1 1 100 100 0 0 0 Y
    58.72802453 1.602521757
    45.64201941 1.602521757
    45.64201941 2.002290401
    58.72802453 2.002290401
    58.72802453 1.602521757
    58.72802453 1.602521757
    END
    0 6 -1 N 12 1 1 100 100 0 0 0 Y
    59.12723737 1.602664404
    58.72746796 1.602664404
    58.72746796 9.612774012
    59.12723737 9.612774012
    59.12723737 1.602664404
    59.12723737 1.602664404
    END
    0 6 -1 N 13 1 1 100 100 0 0 0 Y
    59.5352047 9.606408035
    58.32980231 9.606408035
    58.32980231 23.99712339
    59.5352047 23.99712339
    59.5352047 9.606408035
    59.5352047 9.606408035
    END
    0 6 -1 N 14 1 1 100 100 0 0 0 Y
    45.64484635 1.798264851
    32.84169375 1.798264851
    32.84169375 1.999847125
    45.64484635 1.999847125
    45.64484635 1.798264851
    45.64484635 1.798264851
    END
    0 6 -1 N 15 1 1 100 100 0 0 0 Y
    45.65068632 0.3914119619
    32.84753407 0.3914119619
    32.84753407 0.5929942359
    45.65068632 0.5929942359
    45.65068632 0.3914119619
    45.65068632 0.3914119619
    END
    0 6 -1 N 16 1 1 100 100 0 0 0 Y
    32.84169375 1.600078506
    19.93059112 1.600078506
    19.93059112 1.999847125
    32.84169375 1.999847125
    32.84169375 1.600078506
    32.84169375 1.600078506
    END
    0 6 -1 N 17 1 1 100 100 0 0 0 Y
    32.84753407 0.3914119619
    19.93643107 0.3914119619
    19.93643107 0.7911806061
    32.84753407 0.7911806061
    32.84753407 0.3914119619
    32.84753407 0.3914119619
    END
    0 6 -1 N 18 1 1 100 100 0 0 0 Y
    11.52684052 1.399312461
    10.92391452 1.399312461
    10.92391452 8.582487579
    11.52684052 8.582487579
    11.52684052 1.399312461
    11.52684052 1.399312461
    END
    0 6 -1 N 19 1 1 100 100 0 0 0 Y
    19.93002681 1.399460517
    11.52684052 1.399460517
    11.52684052 1.997651904
    19.93002681 1.997651904
    19.93002681 1.399460517
    19.93002681 1.399460517
    END
    0 6 -1 N 20 1 1 100 100 0 0 0 Y
    19.93643107 0.3963674765
    10.23509144 0.3963674765
    10.23509144 0.9945588887
    19.93643107 0.9945588887
    19.93643107 0.3963674765
    19.93643107 0.3963674765
    END
    0 6 -1 N 21 1 1 100 100 0 0 0 Y
    10.83581137 0.9945596507
    10.23509144 0.9945596507
    10.23509144 7.782923798
    10.83581137 7.782923798
    10.83581137 0.9945596507
    10.83581137 0.9945596507
    END
    0 6 -1 N 22 1 1 100 100 0 0 0 Y
    10.23509144 7.18220407
    0.03609072956 7.18220407
    0.03609072956 7.782923798
    10.23509144 7.782923798
    10.23509144 7.18220407
    10.23509144 7.18220407
    END
    0 6 -1 N 23 1 1 100 100 0 0 0 Y
    10.93696799 7.981767851
    0.7379672786 7.981767851
    0.7379672786 8.582487579
    10.93696799 8.582487579
    10.93696799 7.981767851
    10.93696799 7.981767851
    END
    0 6 -1 N 24 1 1 100 100 0 0 0 Y
    0.6390151778 7.782923798
    0.03609072956 7.782923798
    0.03609072956 23.98320605
    0.6390151778 23.98320605
    0.6390151778 7.782923798
    0.6390151778 7.782923798
    END
    0 6 -1 N 25 1 1 100 100 0 0 0 Y
    1.554119012 8.582487579
    0.7379672786 8.582487579
    0.7379672786 23.98397036
    1.554119012 23.98397036
    1.554119012 8.582487579
    1.554119012 8.582487579
    END
    0 6 -1 N 26 1 1 100 100 0 0 0 Y
    2.304036029 9.983319474
    1.652782746 9.983319474
    1.652782746 23.98161545
    2.304036029 23.98161545
    2.304036029 9.983319474
    2.304036029 9.983319474
    END
    END GEO
    OPT
    MAX 100
    VARS
    END
    END OPT
    VARSWP
    END VARSWP
    QSG
    IMPORT YES
    EXTRA_METAL YES
    UNITS YES
    ALIGN YES
    REF NO
    VIEW_RES NO
    METALS NO
    USED YES
    END QSG
    Last edited by promach; 17th August 2019 at 04:42.

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  2. #2
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    Re: Balun design gives box resonance error in Sonnet

    Do you realize that the Sonnet box wall is a metal boundary? Like a metal box? You have a line from port 3 directly at the box wall, that looks wrong to me. Also, the lines at port 1 might not be what you really want ...

    Post a sketch what your design should look like. It's difficult to see from your Sonnet model what ground connection is intended and what is user mistake.

    For the box resonance, did you check the Sonnet manual? Air layer thickness and top conver "free space" are something to look at.



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    Re: Balun design gives box resonance error in Sonnet

    Well, this is not planar marchand balun. This balun topology does not require vias connections to ground.

    By the way, you can just run the Multi-Section_Coupled_Line_Balun.son design file using only free SonnetLite software




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    Re: Balun design gives box resonance error in Sonnet

    I don't need Sonnet Lite because I have Sonnet Professional and was part of the Sonnet support team for many years. That's why I say your model looks totally wrong!

    Quote Originally Posted by promach View Post
    Well, this is not planar marchand balun. This balun topology does not require vias connections to ground.
    Sure, but you have several of your lines VERY close to the METAL SIDE WALLS.
    Some lines touch it, that creates a connection to ground.
    Some are close, that changes the line behaviour.

    But just like the other thread, you don't answer my questions. Then it's a waste of time to answer here, so: Good luck!



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    Re: Balun design gives box resonance error in Sonnet

    Sure, but you have several of your lines VERY close to the METAL SIDE WALLS.
    Some lines touch it, that creates a connection to ground.
    Some are close, that changes the line behaviour.
    I have already tried modifying the box size, but it does not really help.




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    Re: Balun design gives box resonance error in Sonnet

    You're closing the Box with Perfect Conductor and 20mm Height is not enough.Make the Box Free Space Enclosure or increase the Air Height..



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    Re: Balun design gives box resonance error in Sonnet

    Quote Originally Posted by promach View Post
    I have already tried modifying the box size, but it does not really help.
    You have multiple mistakes in your model.

    At least you have now removed the short circuit between the feedline at port 3 and the box wall.
    The next question is if the two lines left and right from port 1 must be shorted to ground? At the moment, they are shorted to ground because they connect to the box wall.

    One of multiple issues is to fix the box resonance issue. I changed top cover to free space and reduced (!) the box height to 10mm. It seems that is enough to supress the box modes.

    Model is attached below.
    Now you need to fix the other issues, e.g. lines left and right from port 1 grounded by touching wall, which might be correct or not.
    Then, you can think about making resuöts more accurate (mesh, thick metal).

    Click image for larger version. 

Name:	cpl1.jpg 
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ID:	155034
    Click image for larger version. 

Name:	cpl2.jpg 
Views:	3 
Size:	222.0 KB 
ID:	155035

    Multi-Section_Coupled_Line_Balun.zip


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    Re: Balun design gives box resonance error in Sonnet

    Make the Box Free Space Enclosure or increase the Air Height..
    Free space as in vacuum ? then this will only work well within simulation.

    I already tried to increase the Air layer height to 40mm , but I just got more box resonance errors.



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    Re: Balun design gives box resonance error in Sonnet

    Quote Originally Posted by promach View Post
    Free space as in vacuum ? then this will only work well within simulation.
    Circuit > Box > Covers

    Yes, the metal box causes box resonances and that is a real effect. The practical solution is the same what "free space" setting in Sonnet does: using absorbing material at the cover, to take out the radiated energy that would otherwise cause box modes.

    ~~

    Don't miss my post #7 above.

    - - - Updated - - -

    Are you sure about materials and/or dimensions? The feed line width of w=1.2mm on 2mm FR4 gives line impedance around 80 Ohm ...



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    Re: Balun design gives box resonance error in Sonnet

    I downloaded your zip file but I still find that box resonance errors are still not suppressed as you had stated in post #7

    Did I miss anything ?





    Are you sure about materials and/or dimensions? The feed line width of w=1.2mm on 2mm FR4 gives line impedance around 80 Ohm ...
    Wait, which segment were you referring to ? and what is wrong with around 80 ohms ? There is no impedance transformer here though






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    Re: Balun design gives box resonance error in Sonnet

    Quote Originally Posted by promach View Post
    I downloaded your zip file but I still find that box resonance errors are still not suppressed as you had stated in post #7
    Yes, you miss something. That dialog shows possible box modes based on box dimensions. It does not evaluate if the box modes are actually excited, or surpressed by free space absorbing boundary.

    One test for the actual presence of box mode is to have a model with just the feed structure, and see if you get sharp resonances (the box modes) in reflection or transmission. As you can see, it is all smooth and flat in "my" model, so there is no issue with box modes for my configuration.

    Click image for larger version. 

Name:	test_boxmode.jpg 
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ID:	155055

    For comparison, this is what you get when the "free space" is changed to "lossless" top cover:

    Click image for larger version. 

Name:	metalcover.jpg 
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ID:	155057

    With the metal box all around, there are multiple box resonances visible in results. You will notice that adaptive frequency sweeps takes many extra points to modell all those resonances. Solution as shown above: with top cover changed to "free space" these resonances are all gone.

    Quote Originally Posted by promach View Post
    Wait, which segment were you referring to ? and what is wrong with around 80 ohms ?
    Nothing is wrong with 80 Ohm if this is what you designed. I just expected the feed lines at port 2 and 3 to be 50 Ohm, as usual.

    The part that I'm still not sure about, after looking at your reference drawing: how to interpret these ends of the lines next to port1? Is that meant to be open or grounded? In your Sonnet model it's grounded to the box.

    Click image for larger version. 

Name:	gndornot.jpg 
Views:	2 
Size:	12.3 KB 
ID:	155056
    Last edited by volker@muehlhaus; 18th August 2019 at 13:27.



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    Re: Balun design gives box resonance error in Sonnet

    One test for the actual presence of box mode is to have a model with just the feed structure, and see if you get sharp resonances (the box modes) in reflection or transmission. As you can see, it is all smooth and flat in "my" model, so there is no issue with box modes for my configuration.
    Wait, why just the feed structure for this box mode test ?


    after looking at your reference drawing: how to interpret these ends of the lines next to port1? Is that meant to be open or grounded?
    I am not sure. I need to email the original authors of the paper regarding this. I will get back to this post once they reply.

    Besides, something else is not right with the layout or ports. See the phase difference (S12-S13)




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    Re: Balun design gives box resonance error in Sonnet

    Quote Originally Posted by promach View Post
    Wait, why just the feed structure for this box mode test ?
    This uses the feed structure as a "probe" to excite the box modes. Sonnet box = cavity resonator, feed lines couple into that resonator. If there is no spurious transmission in that case, your actual model results should be good. At least for these low order box modes.

    (It's a bit more complex that what I describe here, but I try to keep it simple).

    Quote Originally Posted by promach View Post
    I am not sure. I need to email the original authors of the paper regarding this. I will get back to this post once they reply.
    Besides, something else is not right with the layout or ports. See the phase difference (S12-S13)
    That might be a result of the balun at port 1 with the open/ground uncertainty. When you contact the authors, also ask about the substrate that they used. I doubt they used 2mm FR4.



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    Re: Balun design gives box resonance error in Sonnet

    That might be a result of the balun at port 1 with the open/ground uncertainty. When you contact the authors, also ask about the substrate that they used. I doubt they used 2mm FR4.
    See page 4 of the paper




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    Re: Balun design gives box resonance error in Sonnet

    Ok, then the ground connection by touching the box walls is perfectly correct!

    The substrate is also specified: er=4.2 with 1.5mm thickness (not 2.0mm as in your Sonnet model). But then, for the 50 Ohm mentioned in the paper, the feed line width at ports 2/3 would much wider than the 1.2mm found in your model. Something is wrong there.


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    Re: Balun design gives box resonance error in Sonnet

    I have drawn the layout precisely in AutoCad as mentioned in the paper and there are some dimension errors.I couldn't catch the electrical response in AWR Axiem and Sonnet..



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    Re: Balun design gives box resonance error in Sonnet

    The substrate is also specified: er=4.2 with 1.5mm thickness (not 2.0mm as in your Sonnet model). But then, for the 50 Ohm mentioned in the paper, the feed line width at ports 2/3 would much wider than the 1.2mm found in your model. Something is wrong there.
    Something else is not right.

    I have attached the Sonnet design file at the end of this post






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    Re: Balun design gives box resonance error in Sonnet

    Quote Originally Posted by promach View Post
    Something else is not right.
    How did you calculate the width and gap in the coupled line sections?
    The coupled line sections all line up exactly at the outside, so are the gaps actually calculated?

    Click image for larger version. 

Name:	zoozoe.jpg 
Views:	7 
Size:	231.5 KB 
ID:	155090

    ~~

    Another (fundamental) issue is that your simulation mesh is rather coarse, and Sonnet will simulate the geometry snapped to that coarse grid. You would need a smaller cell size for accurate results, to capture the true gap width and line width.

    ~~

    But it seems that Bigboss has already simulated using fine mesh, with results that don't agree, so there is something wrong with the layout also.
    Last edited by volker@muehlhaus; 20th August 2019 at 08:17.



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    Re: Balun design gives box resonance error in Sonnet

    Volker,

    Controlled Impedance Analyzer and Transmission Line Tool give different results for Edge-to Edge Coupled Lines for the same Input data, do you know why ??



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    Re: Balun design gives box resonance error in Sonnet

    Quote Originally Posted by BigBoss View Post
    Controlled Impedance Analyzer and Transmission Line Tool give different results for Edge-to Edge Coupled Lines for the same Input data, do you know why ??
    Sorry, no idea, I never used Controlled Impedance Analyzer and don't know what method they use.



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