A question about a "sag" in bode plot

[bhl777]

Hi All, when I measured bode plot of a loop, I saw a sag in -20dB/dec. Attached is the picture, could anyone advise what happened in this sag? I doubt there is a pole-zero pair and cause this, but not sure if it is correct. Thank you very much!

 

[barry]

How did you get this plot? Was this measured by an instrument? If so, then it's probably correct. You don't give us a lot of information. What is it you are looking at the response? If it's a real-world system then there are probably all sorts of parasitics that you're not aware of.