simulate 50-ohm transmission line
how to know a 50-ohm transmiion line is good or not good ???
when I simulate 50-ohm transmission line with EM simulator~~
what kinds of charts should I observe ???
smith chart or cartesian ????
Hi myem,
When simulating a 50-ohm transmission line, the important thing to observe is would be the s-parameters.
You could view it either with the smith chart or the cartesian.
HI myem
I think when you use transmission line which character impedance is 50ohm ,you should konw the load impedance that is 50ohm or not .Then you can estimate the transmission line is good or not in Smith chart.
In fact, EM simulation of 50 ohm line is just a rough estimation (of course it is more accurate than just S-parameter simulation). At higher frequency (>10 GHz), the computation will still have some difference between simulation and measurement. Smith Chart is the best way of knowing how close your line closed to 50 ohms.
There is no perfect 50Ohm in the world, return loss under -25dB is OK!
smith chart is the best.
Just put a plot of S11 (Should be the same as S22) and S21.
S11 should be lower that ~ -35dB and S21 ~<0dB.
Assuming you have a 50 ohm 1 wave length line at your
desired Freq.
Hi,
just to join this interesting discussion with a somewhat changed point of view. When simulating in EM simulator and ploting S parameters on a Smith chart, you will for sure see what simulator "thinks" is a 50 Ohm line, this might not neccessarily be the 50 Ohm in practice for a number of reasons.
First, as stated above, deffinition od characteristic impedance is not unique even in theory. Different simulators use different methodologies for computing Zo so the results might be different. Difference can increase when accounting finite metal thickness. Furthermore, user can contribute to an error by uncareful definition of ports, meshing or other computational parameters. Also, some amount of structure idealization considering uniform line width and absence of surface roughness are neccessary to introduce in simulations. Finally, EM simulators are just the tool, not the absolute true!
To completely disapoint everybody, not even measurements are a good proof that any line has 50Ohm impedance, it is for certain a proof for pure TEM lines, for hybrid wave lines this is a mater of luck and chance.
flyhigh