vna display s11 s22 smith
Because VNA just can measure s-parameter.
How can I measure it ?
If I get the S-parameter from VNA , how can transfer it into Z0 ??
one of the VNA feature is the "SMITH CHART"
so push the smith button and you will get the impedance
of your microstrip line on your VNA.
Hi I've never seen a VNA in real life but I've read about the animal Start with an open circuit. and measure S11. At lenght l from the opencircuit the impedance will be Zoc=-j*R0*cot(beta*l).
The impedance at length l from the open circuit is
S11 corresponds to a certain impedance S11_oc=Zoc-Z0/(Zoc+Z0), solve for Zoc.
replace the opencircuit with a short, measure S11. Solve for Zsc
Zsc at length l will vary as j*R0*tan(beta*l)
As you can see from the mathematical relations the characteristic impedance (real) R0 will be found as sqrt(Zoc*Zsc)
Kindest regards,
StoppTidigare
Hi, if you just want to see the performance of your 50 ohm transmission line (presumably, you have a jig with suitable connectors) with VNA, just do a full 2port calibration across your frequency band of interest. After calibration, you can see the insertion loss and return loss.
If you have done the design properly, you should get good return loss ( better than -15dB) at port 1 and port 2, that is, the line is well matched to the 50 charactersitic imped of VNA. If you display the VNA in smith complex chart format, you should see your S11, S22 plots centered at middle of the dsplay, at your frequency band.
Hi,
besides everything being said so far, just make sure your 50Ohm calibration standard is better, i.e. has lower reflection than the 50 Ohm line you are measuring. It is because the reflection standard provided with some callibration kits is not great at all frequencies, it varies and should be better than -30dB for all of the freq range you are interested in. You cannot measure reflection beyond that standard more accurately (and you might not need it accurately as well so this should not be the limitation in general).
flyhigh
complicated answers to a simple question!!! after calibrating your cables and connectors, connect your sample and measure S11 [or S22 if its symmetrical], press the appropriate button to get the Smith Chart. The center of the Smith Chart is typically 50 Ohms-- see where your curve falls-- good VNA's will allow a marker that tells you the impedance [S,Z,Y] directly.