Hi Roger
Thanks for all this papers and sharts, here my simple direct measurements comparaison of this morning for the same balun 1/1 commun mode impedances done by two differents methods :
1) S11 Shunt IZI responses ( commun mode connections).
2) S21 IZ_Seriall response ( commun mode on serial connection).
see illustrations attached below , it gives a very different impedances result , that's Why the S11 IZI is not usable here due to high values of impedance measurements where S21 Serial methode is still a very correct methode .
Conclusion : S21 Serial impedance or LogMag is the only correct methode to mesure the commun mode rejection of baluns Z> 1KOhm ( or any S21 derived nanoVNA graphes ) .
73's Nizar
