Hi Dave,
S21 is the gray, I think (the not yellow one -- I'm color blind) print at the top right of the screen in the last two images I posted. It's line is flat at 0 dB across the frequency range with the test rig shorted and gives the unusual curve I showed when the filter is used. Connecting the Ports 0 & 1 of the VNA together (without the test rig) also show 0 dB flat across the frequency range. Is that what you meant?
Many thanks.
Mitch NK3H
