I have a question about measuring filters below the low end of any Nanovna.

Is it possible to extrapolate both S21 and S11 down to DC on the Nanovna? I am looking for a way to measure some low pass filters I built from 0 to ~20KHz (audio range) without costing a ton of money. I do not have access to a Frequency Response Analyzer.  Any thoughts or suggestions would be very much appreciated.
Thank you,
Ken M.