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5th May 2011, 10:36 #1
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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.

5th May 2011, 10:36

9th May 2011, 07:42 #2
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Re: Interdigital capacitor in HFSS
can you get the sparameters?

9th May 2011, 08:25 #3
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Re: Interdigital capacitor in HFSS
Here, S11 and S12.

9th May 2011, 08:34 #4
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Re: Interdigital capacitorp in HFSS
Again, but imag and real part.

9th May 2011, 08:34

9th May 2011, 19:41 #5
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Re: Interdigital capacitorp in HFSS
since you have sparameters you should be able to get the capacitance. There's a relatively simple transformation to go from sparam to Yparam
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 sparams 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 sparams
yp=s2y(s2p,Z0); % Yparams
y11=reshape(yp(1,1,:),1,length(F));
C11=imag( y11)./(2*pi*F); % capacitance
L11=imag(1./y11)./(2*pi*F); % inductanceLast edited by rntsay; 10th May 2011 at 06:27.
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9th May 2011, 19:41

10th May 2011, 09:28 #6
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Re: Interdigital capacitorp in HFSS
Should I use S12 or S11 parameters? Can you explain? Thank you

10th May 2011, 19:31 #7
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Re: Interdigital capacitorp in HFSS
you should use the full sparam 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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11th May 2011, 09:58 #8
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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.

11th May 2011, 21:12 #9
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Re: Interdigital capacitorp in HFSS
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11th May 2011, 21:12

18th June 2011, 19:17 #10
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Re: Interdigital capacitorp in HFSS
Why don't you use y parameters calculated by HFSS?

19th June 2011, 00:24 #11
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Re: Interdigital capacitorp in HFSS
sure,also you can directly export the yparameter to do it.
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