Hey all, Refer to page 5 in the pdf in the link (http://whites.sdsmt.edu/classes/ee481/notes/481Lecture26.pdf) I am having a little bit of a hard time understanding a portion of a derivation. You will notice that when determining the ABCD paramters of the shunt stubs they merely use A=1, B=0, C=Y, D=1. However, they do not use A=1, B=Z, C=0, D=1 for the 1/4λ transmission line (which would be used to describe a series impedance). Why can they treat the stubs as an impedance when determining the ABCD parameters, but the 1/4λ wave section has to be treated as transmission line? They are both sections of transmission line, but the stub can be treated as a lumped element?