negative group delay of S21

[yasine79]

Hi all!

i made a transmission measurement (S21) with the VNA. the frequency range is 2 to 4 GHz. the DUT between the two antennas was a teflon plate. the distance between the antennas was 50 cm. I was surprised to conclude that the group delay (tau) is negative. What does mean a negative time? did i make a mistake in the measurement?

thank you all.

 

[BigBoss]

You did probably a calibration error.You should do this calibration with SOLT technique to get the right phase results.

 

[FvM]

How did yout setup VNA calibration? What's the transmission reference?

 

[shrivishal]

Negative time in group delay reflects the poor coupling in the structure. It is not a big problem. It can be corrected by making changes in the structure.

 

[biff44]

well, make a bunch of these, put them in series, run the nasdaq stock ticker thru a modulated wireless link using them, and make your stock market moves ahead of everyone else!