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    Interdigital capacitor in HFSS

    Hi,
    I designed IDC in HFSS (see attached pics and HFSS file). How can I see capacitance of such IDC?

    P.S. this is IDC on alumina substrate, just to see how it works in HFSS. Later I will make it on high permitivity BST material.

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    Re: Interdigital capacitor in HFSS

    can you get the s-parameters?



    •   Alt9th May 2011, 07:42

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    Re: Interdigital capacitor in HFSS

    Here, S11 and S12.



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    Re: Interdigital capacitorp in HFSS

    Again, but imag and real part.



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    Re: Interdigital capacitorp in HFSS

    since you have s-parameters you should be able to get the capacitance. There's a relatively simple transformation to go from s-param to Y-param
    and from that capacitance (or inductance). There should be a past post in this forum that describes this. Looking at your graphs I'd expect there
    to be a complicated frequency dependence. I usually write out the s-params into an .s2p format file and process the data in matlab.

    Here's a matlab sniplet : (needs rf circuit package)

    F=your frequency range
    Z0=intrinsic impedance (usually 50)
    s2p=your s-params

    yp=s2y(s2p,Z0); % Y-params
    y11=reshape(yp(1,1,:),1,length(F));
    C11=imag( y11)./(2*pi*F); % capacitance
    L11=imag(1./y11)./(2*pi*F); % inductance
    Last edited by rntsay; 10th May 2011 at 06:27.


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    •   Alt9th May 2011, 19:41

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    Re: Interdigital capacitorp in HFSS

    Should I use S12 or S11 parameters? Can you explain? Thank you



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    Re: Interdigital capacitorp in HFSS

    Quote Originally Posted by vfurlan View Post
    Should I use S12 or S11 parameters? Can you explain? Thank you
    you should use the full s-param matrix which in your case is a 2x2 matrix ((S11,S12),(S21,S22)) for each frequency point analyzed.
    So the variable "s2p" above is a 2x2xN array : the last index runs over the number of frequency points analyzed.
    The "s2y" function transforms "s2p" into another 2x2xN array ((Y11,Y12),(Y21,Y22)). Then Y11 can be used to get capacitance,...
    Your "capacitance" could be frequency dependent (not constant)


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    Re: Interdigital capacitorp in HFSS

    S parameteres have to be in re +i*imag form of course?!
    How do you export files in s2p format from HFSS? I do not have this option, although it is not a problem, I can perfectly well export in txt.



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    Re: Interdigital capacitorp in HFSS

    Quote Originally Posted by vfurlan View Post
    S parameteres have to be in re +i*imag form of course?!
    How do you export files in s2p format from HFSS? I do not have this option, although it is not a problem, I can perfectly well export in txt.
    I'm running and older version (12.1) (don't have 13 unfortunately). What I use there is : (menu tabs)

    HFSS -> Results -> SolutionData -> ExportMatrixData

    There's also an EquivalentCircuitExport which I haven't used


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    Re: Interdigital capacitorp in HFSS

    Why don't you use y parameters calculated by HFSS?



    •   Alt18th June 2011, 19:17

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    Re: Interdigital capacitorp in HFSS

    sure,also you can directly export the y-parameter to do it.



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