S12 and S21 are the same
I have a simple questions about the S-parameters S12 and S21.
I have two antennas connected to the VNA. If the S12 and S21 are exactly the same. I want to know how the antennas react to each other. I dont understand what it means. There's a picture attached. I don't understand waht happens with s12 and s21 at 4.4 GHz.
Help?
Thank you.
It means that the two antennas transfer energy both directions the same amount.
Check out
http://en.wikipedia.org/wiki/Recipro...romagnetism%29
Basically the power transfered from antenna A to antenna B is the same as from antenna B to antenna A.
That will almost always be the case for antenna, although it will not necessarily be so if there are non-linear devices like ferrites and you use enough power to saturate them.
Devices such as amplifiers will not have S12 and S21 the same.
When 2 antennas are connected to a VNA, S12 and S21 is the isolation between the antennas while S11 is the RL of Ant 1 and S22 is the RL of Ant 2.
If both antennas are the same, then I doubt the calibration of the VNA at port 2. Have you done the through calibration ?
Why would you suspect the calibration of the VNA if S12 = S21 ? That is what he said happens, and that is what I would expect.
Irrespective of whether antenna A and antenna B are the same or not, one would expect S12 and S21 to be the same.
I doubted the calibration as S22 is not a very smooth curve.
I'd not looked at his graph - only his words. Yes, it does look a bit odd.