When I first started doing microstrip RF distributed elements like UHF notch filters I was really confused by the results I was getting from my $400 pocketVNA.

When I first started doing microstrip RF distributed elements like UHF notch filters I was really confused by the results I was getting from my $400 pocketVNA. The microstrip filters worked when I had them in my physical RF pipeline but the S11 I was measuring was crazy. Eventually I gave up. One day while complaining on IRC someone suggested I let the VNA warm up before doing the calibration routine. I'd just been doing it right after turning it on because naturally, that's what was required first. I waited 15 minutes and then did the calibration. Suddenly the S11 plots actually matched the behavior and I could compare directly against the sonnet fullwave sim design instead of just "it seems to work".