Hi,
Now, in CST the S-parameters are normalized by default to a value that minimizes the reflections. This value changes with frequency because the wave impedance changes with frequency. Thus, these S-Parameters are normalized to a frequency dependent impedance in order to obtain minimum reflections over the whole frequency range (similar to HFSS). In your case this impedance is the wave impedance of the fundamental mode. By normalizing the S-Parameters to 50 ohms ( a value that is chosen arbitrarily and does not correspond to any physical quantity in your deign) you effectively eliminate the frequency dependency and normalize the S-Parameters to a value that does not minimize reflections (it's not matched to the port). Once you've done this, you are not allowed to use the formula you mention above since Z0 is now known a priori (50 ohms) so you cannot solve for it.
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Hi stergios thanks for you reply! DO you have any relation with Greece?cause your name is common here :lol: So i want to be sure if the
Zo of the feed port is always 50 Ohm or not ? I now that when we make an antenna for example the feed ports have specifics resistance (50,75,100) so i want to be sure if my structure is realestic. Ι am a little puzzled ...
So you say to me that if i activate the "normalize to 50 ohms" is not good if i want to represent my structurre for real (?) You can take a look to some images that i have uploaded before.I don't have feed line in my structure, i have a waveguide port only:???:. I thought that Zo of the waveguide port depend on geometry of the port(it is constant i don;t change) and from (R,C,er of port) but i don't change them. So the Zo should not change.... !!! :idea: So the Zo shouldn't change if i activate 50 ohm option or if i don't activate it? This i don't understand. I think tha s parameters change when Zin(of waveguide) change (for example if i change the material but i though that the Zo of the port is constant. With activate 50 i have s11 magnitude 0.96 and without it 0.40. Which is real? Damn
From the other post : Icase) Without normalize to 50Ohm, for e=2 and some specific dimensions, a waveguide port gives |s11|=0,40 phase=93degrees and |Zin|=|0.29+i2591|=2591Ohm with phase=89 ,also VSWR=2,31.
IIcase) With normalize to 50Ohm the same one is: |s11|=0,94 with phase=14degrees, and |Zin|=|0.39+i2591|=2591 ohm and phase=89, also VSWR=36,13 .
I am so newbie and i am sorry for not understand some thinks.Thanks a lot for all
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As I wrote in your other thread, the waveguide port Z0 is not fixed ("generalized S-parameters"). It depends on the waveguide dimensions. If you fill the waveguide with dielectric, that will also change the impedance.
See "Wave impedance in a waveguide"
https://en.wikipedia.org/wiki/Wave_impedance
Hey bro thanks for your answers. I understand that if i change the Zin (of the waveguide) change S11 and Zo. But in real structure the ports have constant resistance Zo. So, the question is To activate or NOT the option of CST "normalize to 50 ohm".