S12 and S21 are the same

[eskim_urtigas]

Hi everyone,

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.

 

[flatulent]

It means that the two antennas transfer energy both directions the same amount.

 

[DeboraHarry]

Hi everyone,

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.

Check out

https://en.wikipedia.org/wiki/Reciprocity_(electromagnetism)

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.

 

[vedagarbhamsandeep]

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 ?

 

[DeboraHarry]

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.

 

[vedagarbhamsandeep]

I doubted the calibration as S22 is not a very smooth curve.

 

[DeboraHarry]

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.