how to get capacitance from 2-port S parameter measurement

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s parameter to capacitance

I've saw many article discuss inductor measurement and modeling.

Recently I meet problem to get a capacitance from 2-port S parameter measurement of a interdigital capacitor.

Thanks for discuss and reply.
 

2 port capacitance

use TRL calibration and make the full 2-port calibrate, then do test on VNA.Save the measurement result in Touchstone formats and use circuit simulator to extract the equivalent parameter.
 

trl measure capacitor

you can use circuit fit to the S parameter.
to do this,many tool can be use,such as MWO...
 

capacitance s11

Hi
just use some formulas that relate the the Sij parameters to the measured or simulated line structure:

- ch(g.l)=((1+S11)*(1-S22)+(S12*S21))/(S12+S21)

- Zc=
Zr*sqrt(((1+S11)*(1+S22)-(S12*S21))/((1-S11)*(1-S22)-(S12*S21)))

- R = Real(g*Zc)
- L = (Imag(g*Zc))/w
- C = (Imag(g/Zc))/w
- G = Real(g/Zc)

g: is the propagation constant =a+jb (a: attenuation, b=2*pi/wavelenght)
R: resistance
L: self induction
C: capacitance
G: admittance
Zc: Characteristic impedance
l: length of the line
ch: hyperbolic cosine
Zr: Characteristic impedance of the measurement system: usually 50Ohm
 
circuit simulator to extract capacitance

A less formal method (compared to the proposed by elek_fyc), is put the 2port s matrix into a linear simulator (ADS, Harmonica, MWO Genesys, etc), then short port 2 to GND, now you have an 1 port circuit. analyze and plot s11 in R+jX. format.
The imag. part is the reactance.

Give me the possibility to add a short note about real part: The equivalent Series Resistance. For my opinion, the typical accuracy of VNA measurement is not sufficient to get accurate knowledge of tand (or Q or ESR)
 

extract capacitance from s-parameters

use the network analyazer to measurement
 

determining capacitance from s-parameters

pewang said:
use TRL calibration and make the full 2-port calibrate, then do test on VNA.Save the measurement result in Touchstone formats and use circuit simulator to extract the equivalent parameter.
Click to expand...

I agreed with pewang. TRL is an accurate way to measure the inductance and perform deembedding for capacitance extraction.
 

Re: how to get capacitance from 2-port S parameter measureme

Hallo Everyone,

elek_fyc, where did you get all this formulas from...... do you have the references where I can go and look them up....?
 

You can measure the 2 port Y parameter, or convert the S parameter to Y parameter, or simulate with a tool to get the Y parameter from S parameter file. After you get the 2 port Y parameter, you can get the capacitance with this:
C = -1/(imag(1/Y11)*2*pi*freq)
where, freq is the frequency correspinding to the S parameter data.
 

    V

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Here, elek_fyc posted how to get capacitance in terms of s parameters. But if i want to get the capacitances of a parallel coupled line (microstrip), then there is two types of capacitances involved, gap capacitance (cg) and parallel capacitance (cp)...how can i get the specific capacitance values from the s parameters? Can anyone please tell me ....
 

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